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Biocompatible Nanocapsules for Self-Healing Dental Resins and Bone Cements
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  • Sydney Menikheim
    Sydney Menikheim
    Department of Chemical, Biochemical, and Environmental Engineering, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, United States
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  • Joshua Leckron
    Joshua Leckron
    Department of Chemical, Biochemical, and Environmental Engineering, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, United States
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  • Michael Duffy
    Michael Duffy
    Department of Mechanical Engineering, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, United States
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  • Marc Zupan
    Marc Zupan
    Department of Mechanical Engineering, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, United States
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  • Amber Mallory
    Amber Mallory
    Naval Medical Research Unit SA, 3650 Chambers Pass Bldg #3610, JBSA Fort Sam Houston, Houston, Texas 78234, United States
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  • Wen Lien
    Wen Lien
    59th Medical Wing, Lackland AFB, San Antonio, Texas 78236, United States
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  • Erin Lavik*
    Erin Lavik
    Department of Chemical, Biochemical, and Environmental Engineering, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, United States
    *Email: [email protected]
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    Orcidhttps://orcid.org/0000-0002-0644-744X
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ACS Omega

Cite this: ACS Omega 2022, 7, 36, 31726–31735
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https://doi.org/10.1021/acsomega.2c02080
Published August 31, 2022

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Abstract

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Bone cements and dental resins are methacrylate-based materials that have been in use for many years, but their failure rates are quite high with essentially all dental resins failing within 10 years and 25% of all prosthetic implants will undergo aseptic loosening. There are significant healthcare costs and impacts on quality of life of patients. Self-healing bone cements and resins could improve the lifespan of these systems, reduce costs, and improve patient outcomes, but they have been limited by efficacy and toxicity of the components. To address these issues, we developed a self-healing system based on a dual nanocapsule system. Two nanocapsules were synthesized, one containing an initiator and one encapsulating a monomer, both in polyurethane shells. The monomer used was triethylene glycol dimethacrylate. The initiator capsules synthesized contained benzoyl peroxide and butylated hydroxytoluene. Resins containing the nanocapsules were tested in tension until failure, and the fractured surfaces were placed together. 33% of the samples showed self-healing behaviors to the point where they could be reloaded and tested in tension. Furthermore, the capsules and their components showed good biocompatibility with Caco-2 cells, a human epithelial cell line suggesting that they would be well tolerated in vivo.

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Introduction

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Self-healing materials which can repair and recover functionality without human intervention have drawn significant interest for biomedical materials in the past 20 years. (1) The idea of self-healing materials stems from nature, specifically in the way living multicellular organisms are able to repair themselves without external intervention. (2) Self-healing materials could be exceptionally useful in methacrylate-based systems such as bone cements and dental resins. It is estimated that over 25% of all prosthetic implants will undergo aseptic loosening (3) which includes microcrack formation in bone cement. Aseptic loosening triggers inflammation and bone resorption and generally requires surgical revision. (3) Revision surgeries are technically demanding, expensive and result in low satisfaction rates among patients. (4) Meanwhile, dental diseases are the most prevalent chronic diseases worldwide and are costly burdens to health care services. (5) Tooth decay impacts close to 100% of the population. (6) Modern dental resins avoid the environmental and health concerns with mercury but have poor durability with posterior fillings lasting 3 to 10 years and large fillings lasting less than 5 years. (7)
Most methacrylate-based systems use capsules for self-healing properties. Capsules are easy to implement in both dental resins and bone cements because these systems often contain other filler particles to enhance the mechanical properties of the materials. (8) Initially, the self-healing capsules simply act as an additional filler. The capsules contain components encapsulated by shells (9) that break when a crack propagates through the material releasing components into the crack via capillary action that can then polymerize and heal the matrix. (10) Biocompatibility is essential for self-healing systems used in biomedical applications. One of the first capsule-based systems was a single capsule system containing dicyclopentadiene encapsulated in a poly(urea-formaldehyde) shell that formed a microcapsule (50–200 μm). Grubb’s catalyst was used to initiate the polymerization of the dicyclopentadiene. A number of groups have looked at this system, and the mechanical properties of the repairs are good, (11) but high cost and toxicity concerns curbed this approach. (12,13) More recently, a number of groups have looked at triethylene glycol dimethacrylate (TEGDMA) liquid encapsulated in polymer shells. Poly(urea-formaldehyde) (UF) microcapsules with TEGDMA and N,N-dihydroxyethyl-p-toluidine (DHEPT) were mixed with benzoyl peroxide (BPO), the catalyst, freely added to the resin; self-healing efficiency showed that about 65% of the virgin fracture toughness could be achieved when using 15% microcapsules in a flexural test. (12) Dual UF microcapsule systems consisting of initiator capsules containing BPO and monomer capsules contained 4′-methylenebis(N,N-dimethylaniline) (MBDMA) (the tertiary amine), trimethylol-propane ethoxylate triacrylate (TMPET) (an acrylate monomer), and bisphenol A ethoxy-late diacrylate (Bis-EMA) (an acrylate monomer) led to 75% of the fracture toughness in an epoxy matrix. (14) Because resin-composite restorations are in contact with saliva, an alternative approach using 2-octul-cyanoacrylate in urethane microcapsules has been explored which reacts without the addition of a catalyst and led to an increase in cycles to failure in a bending test. (15) Microcapsules of a solvent, anisole with polymethylmethacrylate (PMMA) were encapsulated in double walled polyurethane/urea-formaldehyde (PU/UF) shells. (16) 50–80% healed fracture toughness was seen in this system.
Polyurethane (PU) has been used in biomedical implants for many years (17) and shows excellent compatibility with blood. (18) Because of their block-copolymer character, PUs have a wide range of versatility in terms of their physical properties and ability to biodegrade. PU, through the years, has proven to be extremely biocompatible as well as thermally stable in the body. (17) TEGDMA is the monomer of choice. BPO is employed as the initiator. The self-healing aspect of the composite is composed of a two-part monomer-initiator polymerization system made solely from materials that are classified by the U.S. Food and Drug Administration as Generally Recognized as Safe (GRAS) to eliminate complications concerning biocompatibility. (12)
While all of these systems can lead to substantial self-healing, the long-term stability and biocompatibility are concerns. We focused on developing a system that would be biocompatible, easily blended into resins, minimally alter critical materials properties like the resin modulus, and provide self-healing behavior. To this end, we investigated single and dual nanocapsule systems based on PU nanocapsules containing nontoxic components. We hypothesized that nanocapsules would impact the mechanical properties of the resin less than larger particles and still lead to a robust self-healing process. To determine the impact of single and dual nanocapsules on self-healing of methacrylate resins, we synthesized PU nanocapsules encapsulating either the initiator or monomer and performed mechanical testing and biocompatibility analysis to determine the feasibility of this system as a self-healing additive for dental resins and bone cements.

Materials and Methods

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Materials

All materials were obtained from commercial suppliers and used without further purification. Sodium dodecyl sulfate (SDS) (BP166, Fisher Scientific) and 99% pure hexadecane (HD) (AC120465000, ACROS Organics) were the surfactant and costabilizer, respectively, used to form the PU nanocapsules. Isophorone diisocyanate (IPDI) 98% (AC427602500, ACROS Organics) and 1,6-hexanediol (HDOH) 97% (AAA1243930, ACROS Organics) were the reactants from which PU was formed. TEGDMA 95% (261548, Sigma Aldrich) was the monomer encapsulated in the PU nanocapsules. BPO (S25672, Fisher Scientific) was the initiator used in the self-healing reaction testing. Butylated hydroxytoluene, 99%, FCC (W218405, Fisher Scientific) was the stabilizer that was encapsulated with the initiator to prevent the BPO from reacting prematurely. The resin used was the West System epoxy resin; this resin was formed with 105 epoxy resin and 209 extra slow hardener. The West System 105 epoxy resin is based on bisphenol A diglycidyl ether, and it exhibits comparable properties to methacrylate-based bone cements and dental resins.
The West System epoxy resin was used as a model of common bioinert biomaterials. Compared to commonly used bioinert biomaterials (such as bone cements), the West System epoxy resin has comparable physical properties. The West System epoxy resin has a density of 1.16 g/cm3. The tensile strength, as defined by ASTM D-638, is 7300 psi. Finally, the tensile modulus, defined by ASTM D-638, is 3.98 × 105 psi for the West System epoxy resin. PMMA is used in total joint replacements to anchor implants to bone. (15) General purpose PMMA (AZO Materials) has a density of 1.18 g/cm3, a tensile strength is 10,153 psi, and a tensile modulus is 4.21 × 105 psi. Likewise, PMMA bone cement has a tensile strength of 5105 psi and a tensile modulus of 3.70 × 105 psi. (19)

Preparation of Monomer Capsules

PU nanocapsules encapsulating TEGDMA were synthesized following procedures previously published in the literature. (20,21) PU nanocapsules were formed via polycondensation in a two-phase system through miniemulsions. In particular, HD and deionized (DI) water formed the two phases, an oil phase and an aqueous phase. SDS was used as the surfactant to confer colloidal stability. In this reaction, SDS helped to control the equilibrium between the rates of fusion and fission during sonication, which ultimately dictated the size of the droplets that form. (18)
Once 70 mL of DI water, 1.145 mL of HD, and 0.88 g of surfactant (SDS) were mixed together at 300 rpm and 40 °C for 1 h, 2.094 mL of IPDI and 6.1 mL of TEGDMA were slowly dripped into the mixture and stirred; this step began the synthesis of the nanocapsules. It is important to note that IPDI is hydrophobic. By dripping the IPDI and monomer into the solution, the IPDI was evenly distributed throughout the oil phase. As the IPDI and TEGDMA entered the pre-emulsification solution, the stirring speed was increased to 400 rpm. Once the IPDI and TEGDMA were fully injected into the beaker, the solution was left to mix at 400 rpm and 40 °C for 10 min. During this step, the solution turned opaque white. Next, the solution was sonicated with a 130-W Ultrasonic Processor with Thumb-actuated Pulser at an amplitude of 38% to break up any IPDI molecules that had aggregated. During this step, emulsions formed, and the solution looked like milk. While sonication was still progressing, an aqueous solution of 5.9 g of HDOH and 10 mL of DI water was dripped into the system. Because of the high reactivity of the isocyanate, the IPDI reacted immediately with the HDOH at the interface of the two phases. (21)
After sonication, the solution was left to react for 24 h at 40 °C and mixed at 300 rpm. After 24 h, much of the solvent had evaporated and a clear, viscous solution with a solid, white sphere was left in the beaker. The solution was washed to rid it of excess reactants or other contaminants. First, the solution was centrifuged in DI water at 4500 rpm and 4 °C for 30 min. After the centrifugation, a hard, white substance appeared at the bottom of the centrifuge tube, a small semitransparent layer was above the solid layer, and a cloudy, transparent water layer with an oily disk was on top. The disk and the water were removed, and fresh DI water was added to the centrifuge tube. The solution was vortexed and again centrifuged at 4500 rpm and 4 °C for 30 min. After the second wash, the solid, white pellet again appeared at the bottom of the centrifuge tube. The water layer was also present with a smaller oily disk on top. The water (supernatant) was again removed and replaced with fresh DI water. The solution was vortexed and centrifuged at 4500 rpm and 4 °C for 20 min. After this centrifugation, layers similar to those after the second wash appeared. The supernatant was removed, and new DI water was added. The solution was vortexed and centrifuged at 4500 rpm and 4 °C for 20 min for a fourth and final time. After this centrifugation, the centrifuge tube contained mostly clear water and a sticky, solid, white substance at the bottom. The supernatant (the water) was again removed, and the pellet was resuspended in fresh DI water; however, the pellet did not resuspend well. The partially resuspended pellet was then frozen in liquid nitrogen and lyophilized.

Preparation of Initiator Capsules

PU nanocapsules encapsulating BPO and butylated hydroxytoluene were synthesized referencing the same procedures previously published in the literature to encapsulate TEGDMA. (20,21) Again, the PU nanocapsules were formed via polycondensation in a two-phase system through miniemulsions. In particular, HD and DI water again formed the two phases, an oil phase and an aqueous phase. SDS was again used as the surfactant to confer colloidal stability. (21)
Once 70 mL of water, 1.145 mL of HD, and 1.1 g of SDS were mixed together at 300 rpm and 40 °C for 1 h, 0.05 g of BPO, and 0.005 g of butylated hydroxytoluene, resuspended in 2.094 mL of IPDI, were slowly dripped into the mixture and stirred; this step began the synthesis of the nanocapsules. By dripping the IPDI and initiator mixture into the solution, the IPDI was evenly distributed throughout the oil phase. As the IPDI solution entered the pre-emulsification solution, the stirring speed was increased to 400 rpm. Once the IPDI solution was fully injected into the beaker, the solution was left to mix at 400 rpm and 40 °C for 10 min. During this step, the solution remained clear. Next, the solution was sonicated with a 130-W Ultrasonic Processor with Thumb-actuated Pulser at an amplitude of 38% to break up any IPDI molecules that had aggregated. During this step, emulsions formed, and the solution looked like milk. While sonication was still progressing, an aqueous solution of 5.9 g of HDOH and 10 mL of DI water was dripped into the system. Because of the high reactivity of the isocyanate, the IPDI reacted immediately with the HDOH at the interface of the two phases. (21)
After sonication, the solution was left to react for 24 h at 40 °C, mixing at 300 rpm. After 24 h, much of the solvent had evaporated and a clear, viscous solution was left in the beaker. The solution was poured into a centrifuge tube and centrifuged with DI water for a total of five times at 10,000 rpm and 4 °C for 20 min each run. After each run, a distinct white pellet formed at the bottom of the tube. Additionally, after each run, the supernatant was discarded, new DI water was added to the tube, and the pellet was resuspended. After the fifth centrifugation period, the supernatant was again discarded, new DI water was added, and the pellet was then resuspended. The resuspended pellet was frozen in liquid nitrogen and lyophilized. When fully dry, the capsules appeared to be a white powder.

Characterization of Nanocapsules

Capsule Morphology and Size

A vacuum sputter coater (Denton Desk II) was used to deposit a 20 nm layer of gold palladium onto the nanocapsule samples placed on carbon tape on a specimen stub for scanning electron microscopy (SEM) imaging using the Nova NanoSEM 450 from FEI. The surface morphology of the capsules was examined as well as the diameters of the capsules. Transmission electron microscopy (TEM) imaging was performed using a FEI Morgagni M268 100 kV TEM equipped with a Gatan Orius CCD camera. To obtain TEM images, the capsule samples were loaded onto copper grids.

Capsule Size and Zeta Potential

A Malvern ZetaSizer (Nano ZS90) was used to determine the diameter and zeta potential of the nanocapsules via dynamic light scattering (DLS). The nanocapsules were placed in a 1 mg/mL solution of 190 proof ethanol for sizing. This solution was pipetted into a cuvette (14955129, Fisher Scientific) which was placed into the ZetaSizer. The capsules were placed in a 1 mg/mL solution of 10 mM potassium chloride (KCl) to determine the zeta potential. To measure the zeta potential, the solution was inserted into a folded capillary zeta cell (Malvern Store, DTS1070) which was placed in the ZetaSizer. Both the size and zeta readings were performed in triplicate.

Capsule Molecular Components and Structures

Fourier-transform infrared (FT-IR) (PerkinElmer Frontier Optica) spectroscopy was used to produce spectrum to identify the molecular components and structures within the capsules. Gel permeation chromatography (GPC) (Viscotek, VE 2001) was used to measure the molecular weight of the PU in the capsules. The GPC column (PL1110-6504) is of the Agilent Plgel MIXED family. Its phase is MIXED-D, its inner diameter is 7.5 mm, its length is 300 mm, and its particle size is 5 μm. To measure the molecular weight of PU, the capsule samples were first crushed via a mortar and pestle. Then, 10 mg of the crushed sample was resuspended in 1 mL of tetrahydrofuran. This solution was filtered with PTFE membrane syringe filters (Fisher, 09-720-002) into GPC vials (VWR, 89239-024) which were placed in the GPC for characterization. Hydrogen-1 nuclear magnetic resonance (1H-NMR) spectroscopy was used to further determine the structures of the capsules and the encapsulated contents. To perform this NMR, the capsule samples were resuspended in deuterated dimethyl sulfoxide at a concentration of 1 mg/mL.

Preparation of Resins

West System Epoxy Resin

To prepare the epoxy resin, a 4:1 ratio of 105 epoxy resin part 1 was added to the 209 extra slow hardener and mixed together in a paper cup. Then, the monomer capsules were added. The total capsule mass was 3 wt % of the 105 epoxy resin. The capsules were resuspended in 190 proof ethanol in order for the capsules to be well dispersed throughout the resin. The mixture was then poured into dog bone molds and heated with a heat gun. The resin was allowed to dry for 24 h. At that point, the dog bones were removed from the mold and placed in an oven at 200 °C for 20 min to further harden the resin by removing the ethanol from the resin through evaporation.
Blank West System Epoxy resins were also prepared in order to compare the resins with capsules. To prepare the epoxy resin, a 4:1 ratio of 105 epoxy resin part 1 was added to the 209 extra slow hardener and mixed together in a paper cup. 190 proof ethanol was also added to the mixture to create the same consistency as the resin with capsules. The mixture was then poured into a dog bone mold and heated with a heat gun. The resin was allowed to dry for 24 h. At that point, the dog bones were removed from the mold and placed in an oven at 200 °C for 20 min to further harden the resin by removing the ethanol from the resin through evaporation.
For self-healing efficiency testing, West System Epoxy resins were created with the monomer capsules and BPO. To create these resins, a 4:1 ratio of 105 epoxy resin part 1 was added to the 209 extra slow hardener and mixed together in a paper cup. Then, the capsules were added. The total monomer capsule mass was 3 weight percent of the 105 epoxy resin. The capsules were resuspended in 190 proof ethanol in order for the capsules to be well dispersed throughout the resin. Finally, 0.5 g of BPO was added to the mixture. The mixture was then poured into the dog bone molds and heated with a heat gun. The resin was allowed to dry for 24 h. At that point, the dog bones were removed from the mold and placed in an oven at 200 °C for 20 min to further harden the resin by removing the ethanol from the resin through evaporation. A total of four of these samples containing monomer capsules and BPO were created.
A total of six other samples were made for self-healing testing. These samples were prepared the exact same way that the four resins with monomer capsules and BPO; however, in these resins, the initiator capsules were used in place of BPO. The total initiator capsule mass was 3 wt % of the 105 epoxy resin.
Control samples were made. To make the control resins, a 4:1 ratio of 105 epoxy resin part 1 was added to the 209 extra slow hardener and mixed together in a paper cup. Then, 1.5 g of TEGDMA was added. The mixture was then poured into the dog bone molds and heated with a heat gun. The resin was allowed to dry for 24 h. At that point, the dog bones were removed from the mold and placed in an oven at 200 °C for 20 min to further harden the resin. A total of 12 of these control samples were created.

Polishing the Dog Bones

Before fracturing the dog bones, the surface defects in the samples were removed to ensure that the samples did not fracture prematurely. First, the samples were milled to smooth the convex sides of the samples. The samples were then polished using 320, 600, 800, and 1200 grit SiC paper (Allied High Tech Products) on a polishing table. The sanding paper was waterproof, and polishing was performed with water flowing. Polishing was performed with increasing grit because the higher grit created finer and finer scratches which caused less damage to the sample but also removed less impurities.

Fracturing the Capsules

Tension Test

The tension test is one of the most fundamental and common types of mechanical testing. This test applies a pulling force to a material with an axial force until the sample breaks and measures the specimen’s response to the stress. (19) The tension test was performed on a universal testing instrument (Instron electromechanical universal testing system, 3300 series) using a strain rate of 10–3 s–1. A complete profile of tensile properties was obtained. These data resulted in a stress/strain curve which revealed the point of failure, the modulus of elasticity, yield strength, the ultimate tensile stress (UTS), and strain to fracture.
To perform the test, the dimensions of the gauge region of the dog bone sample were first determined. Then, reflective tape was placed at the edge of the gauge region. The reflective tape was used to measure length of the gauge region. Then, the sample was placed in the grips of the machine. During the testing, the grips moved apart until the sample snapped. A laser extensometer performed the strain and elongation measurements during the testing.

Determining Self-Healing Efficiency

Tensile Test

During this test, the monomer capsules was placed in the resin with the BPO initiator. The test proceeded as described above; however, when the resin broke, the two halves were placed back into the dog bone mold and left for 48 h to heal. Then, a second tensile test was performed on the healed resin samples.

Determining Biocompatibility

Cell Culture

The Caco-2 cells (a line of human epithelial colorectal cells) used were obtained from ATCC. The cells were cultured in Minimum Essential Medium–Alpha modification (MEM-α), supplemented with 20% fetal bovine serum (FBS), with both the MEM-α and the FBS having been purchased from ThermoFisher. Cells were grown in an incubator at 37 °C in a 5% CO2 atmosphere.

Live/Dead Assay

The assay was performed using the LIVE/DEAD Viability/Cytotoxicity Kit, for mammalian cells, purchased from ThermoFisher. Calcein-AM was used as the live stain, with live cells appearing green, while ethidium homodimer-1 (EthD) was used as the dead stain, with dead cells being stained red. Images of the cells were taken using an IX81 Olympus fluorescence microscope. The cell count was 350,000 cells/mL, and the cells were mixed thoroughly before being spread out evenly over all 24 wells, leading to a count of 14,500 cells per well. After seeding, the cells were allowed to adhere for 23 h, after which point the testing and control conditions were created. Eight conditions were tested, with each condition having 600 μL of media (80% MEM-α and 20% FBS) present. Three wells contained 1 mg of BPO, three wells contained 10 mg of butylated hydroxytoluene (BHT), and three wells contained 10 mg of TEGDMA. These wells comprised the conditions that were intended to examine cell viability in the presence of the materials encapsulated by the PU nanocapsules. As for examination of cell viability in the presence of the PU nanocapsules themselves, there were three wells in which 10 mg of monomer nanocapsules (capsules with TEGDMA) were present, three wells in which 1 mg of initiator nanocapsules (capsules with BPO and BHT) were present, and three wells in which 10 mg of monomer nanocapsules created with 59 g of HDOH and 20.94 mL of IPDI (10× the usual amount) were present. Finally, there were two control conditions tested, with three wells having just 600 μL of media in them (a live control) and three wells having 100 μL of 10% ethanol present (a dead control). The cells were exposed to each condition for 1 or 24 h, after which point the nanocapsules, the encapsulated materials, and the media were all removed from the wells. The cells in each well were then washed with 650 μL of Gibco HBSS purchased from ThermoFisher. Following removal of the HBSS, 600 μL of fresh media was added to each well. Once fresh media were present in each well, 25 μL of stain was added to each well. The stain was prepared by mixing 8 μL of EthD with 4 μL of calcein and 1 mL of PBS. Following addition of the stain, the cells were allowed to incubate for 45 min at 37 °C in a 5% CO2 atmosphere. After the incubation period had passed, the cells were imaged using the IX81 fluorescence microscope.

Results

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Optimization of Reaction Characteristics for Nanocapsules

PU Reaction

To optimize the monomer and initiator capsules, first the reaction to form PU was optimized. PU is formed by the chemical reaction between a di/polyisocyanate and a diol or polyol; this reaction forms repeating urethane groups. (17)
To form the PU nanocapsules, a 5:1 ratio of HDOH to IPDI was used to ensure that end capping of the IPDI occurred during the reaction. To minimize the size distribution of the PU nanocapsules in the system, the amount of surfactant was varied. For SDS, the critical micelle concentration is 6 to 8 mM. This is the concentration of SDS in a bulk phase, in this case water, above which micelles start to form. In this particular formulation, with a total of 80 mL of DI water, this means that a mass of 0.138 g of SDS or greater must be added in order to form micelles. Guo et al. in “The Role of Surfactant and Costabilizer in Controlling Size of Nanocapsules Containing TEGDMA in Miniemulsion” stated that a typical procedure to obtain PU nanocapsules encapsulating TEGDMA included 0.88 g of SDS and 0.88 g of HD. (21) Torini et al. reported preparing the miniemulsions with 0.66 g of SDS and 0.66 g of HD. (20) The basic procedure for the preparation of miniemulsions is based on the dispersion of HD in the aqueous phase with the surfactant, SDS; however, the amount of HD and surfactant must be varied depending on what is being encapsulated. (20)
In the reaction, the surfactant was anionic and provided stable miniemulsions. (20) The costabilizer allowed for the buildup of an osmotic pressure in the droplets which provided stability against Ostwald ripening. (20) During the reaction, to form both the monomer and initiator nanocapsules, a stable miniemulsion was first obtained when the IPDI was added to the pre-emulsification solution and sonicated. Then, the HDOH was dissolved in the external phase and added to the miniemulsion. This addition leads to the reaction between the IPDI and HDOH at the interface of the two nonmiscible phases (the water and oil phases). (20)

Capsule Characteristics

PU capsules that encapsulate TEGDMA and BPO/butylated hydroxytoluene were synthesized via a polycondensation in a two-phase system through miniemulsions. The capsules are parts of dual- and monocapsule self-healing systems. It was determined that 0.88 g of SDS is the optimal amount of surfactant needed to form nanocapsules near the 200 nm size range with a low polydispersity index (PDI) (Figure 1). The monomer capsules can be synthesized with consistency in size, zeta potential, and chemical composition over multiple batches; however, the samples contained excess TEGDMA. While the excess could be minimized by washings, subsequent adjustments in the protocol to increase the amount of IPDI and HDOH 10-fold essentially eliminated excess TEGDMA.

Figure 1

Figure 1. (A) DLS of TEGDMA nanocapsules. (B) Diameter of nanocapsules was consistent batch to batch. (C, D) TEM images of nanocapsules. (E) FT-IR demonstrating the presence of the PU as well as the TEGDMA. (F) SEM showing the nanocapsules (tan arrows) and residual TEGDMA. Not all of the TEGDMA was encapsulated in this formulation.

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The initiator capsules were synthesized using the same protocol and were composed of PU and encapsulated BPO and butylated hydroxytoluene. It was determined that 1.1 g of SDS is the optimal amount of surfactant needed to form nanocapsules with around the 300 nm size range with a low PDI (via DLS).

Mechanical Testing

The West System Epoxy resin was used as a matrix for testing the impact of the TEGDMA and BPO nanocapsules because the properties of the resin are well known and consistent. The mechanical properties of the resin with the monomer capsules were compared to those of blank resins in order to determine how the capsules affect the resin properties.
Incorporation of nanoparticles into matrices is known to impact the mechanical properties of many systems (Figure 2). (22) Not surprisingly, the nanocapsules studied here impacted the mechanical properties of the matrix. The addition of 3 wt % nanocapsules significantly impacted the mechanical properties. The modulus of the composite was half of that of the matrix alone. Likewise, the nanocapsules impacted the yield stress and the UTS of the resins. The nanocapsules did not impact the strain to fracture values. None of this is unexpected with the addition of nanocapsules to an epoxy resin. In a dental resin or bone cement, there are a number of fillers and other additives. Exchanging one of the fillers for a self-healing component could achieve the desired mechanical properties while adding the self-healing feature.

Figure 2

Figure 2. Incorporating nanocapsules into the matrix. (A) Stress–strain curves for the epoxy resin without nanocapsules (n = 12). (B) Stress–strain curves for samples with nanocapsules (n = 12). (C) Table comparing critical features from these two groups. Adding nanocapsules impacts the mechanical properties of the resin, as expected.

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Following fracture, samples were put back together in the molds to see if there was any self-healing with just monomer capsules. As expected, no self-healing was seen. Following mechanical testing, the fracture surfaces were analyzed using SEM.
SEM revealed that the monomer capsules broke during mechanical testing. Figure 3A,B shows the resin alone. Figure 3C shows the resin with monomer capsules (the very small dots scattered through the fracture surface.) Higher resolution images show that the capsules have broken. Broken capsules can be seen in Figure 3D–F. Larger capsules appear to break more readily than smaller capsules with some smaller capsules still intact on the fracture surfaces.

Figure 3

Figure 3. Images show the fracture surface on samples of West System epoxy resin. (A) This image shows the area at which the fracture occurred in a sample without monomer capsules. (B) This SEM image presents a zoomed in image of another fracture site in the resin. (C) This SEM image shows the fracture surface from a sample with monomer capsules. The capsules, especially larger capsules, are evident in the surface and cause a rougher surface. (D) These SEM images show fracture surfaces another sample with monomer capsules at a higher magnification. In these images, it is evident that some of the larger capsules have cracked. The white dots in these images are the nanocapsules. (E, F) These SEM images focus on the monomer capsules in the resin. These images show fractured capsules in the resin.

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Self-Healing Efficiency

The goal of this work was to determine if incorporating nanocapsules filled with TEGDMA, the monomer, and BPO, the initiator could promote self-healing following fracture.
West System Epoxy resins were prepared with monomer capsules and BPO. The BPO was added directly to the resin and not encapsulated in these experiments. Tensile tests were performed on these samples.
The samples underwent strain to fracture. The elastic moduli, yield stress, and UTS were similar to the previously tested samples. All of the samples were then placed back together in the molds in which the dog bones were cast. After 48 h, two of the four samples exhibited self-healing and could be tested again. Not surprisingly, the self-healed system showed smaller stress–strain curves. Figure 4A shows the stress–strain curves for the samples during the initial tests (R1 and R2) and the stress–strain curves following self-healing (Healed R1 and Healed R2). Figure 4C shows the values for the modulus, yield stress, UTS, and strain to fracture for the as-made versus self-healed samples. While the modulus is maintained or increased for the samples, the yield stress and UTS are significantly decreased.

Figure 4

Figure 4. (A) This figure depicts the stress/strain curves from two of the four samples of resin with the monomer capsules and BPO after self-healing. These samples were prepared at the same time and with the same conditions. The properties of the original resins (R1 and R2) are also displayed for comparative purposes. (B) Stress–strain curves from 2 of the six samples of resin with the monomer capsules and initiator capsules after self-healing. These samples were prepared at the same time and with the same conditions. The properties of the original resins (R4 and R5) are also displayed for comparative purposes. (C) Mechanical properties of R1 and R2, which exhibited self-healing as made and after the self-healing reaction. (D) Mechanical properties of the dual-capsule system as made and after self-healing for the two samples of six that exhibited self-healing.

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Nonetheless, even with the BPO initiator just mixed into the resin, the system exhibited self-healing in some of the samples. As a control, based on this, epoxy resins with TEGDMA (n = 12) were prepared as controls to determine if unencapsulated TEGDMA in the resin has any self-healing effect. These samples were tested with a tensile test. None of the samples showed a self-healing effect confirming that the presence of TEGDMA in capsules is essential for self-healing to occur.
Epoxy resins with monomer capsules and initiator capsules were also prepared. These samples underwent tensile tests. All of the samples exhibited mechanical properties similar to the monomer capsule-alone samples. Of the six samples tested, two exhibited self-healing after 48 h. The stress–strain curves for the as-made (R4 and R5) and healed samples (Healed R4 and Healed R5) are shown in Figure 4B.
Similar to the samples where the initiator, BPO, was dissolved in the resin, the dual nanocapsule systems that exhibited self-healing maintained their modulus but showed substantial drops in the yield stress and UTS. The values for the modulus, yield stress, UTS, and strain to failure are summarized in Figure 4D.
Researchers have proposed multiple definitions of healing efficiencies. We will measure healing by defining a recovery ratio (R). The recovery ratio is shown in eq 1, where f is the partially healing material property and f∞ is the virgin state material property. (23)
(1)
Using this equation, we get the recovery ratios shown in Table 1.
Table 1. Recovery Ratio for Each Property Examined for the Resin Samples after Self-Healing
 elastic modulusyield stressUTSstrain to fracture
R12.8330.2620.3330.161
R21.2430.2790.4880.595
R40.8330.0940.0860.362
R51.0230.1300.1790.520
As expected, while the modulus was maintained in the self-healed samples, the yield stress, UTS, and strain to fracture all dropped for both the system with the initiator mixed directly in the resin (R1 and R2) and for the dual initiator and monomer capsule system.
The tensile test is an excellent test for looking at whether a self-healing system works, but it would be relatively rare for a dental resin or bone cement to be in tension under normal conditions. It is more common that in use, a resin or cement would experience crack propagation. Having a system that can promote self-healing, even if the original yield stress or UTS are compromised would still be very valuable.

Biocompatibility

This self-healing system was built around materials that are designed to be extremely biocompatible. To test whether the biocompatibility was achieved in the practical system, we performed a series of live-dead assays on the components and nanocapsules. The results of the biocompatibility studies are presented in Figure 5 as well as Figure S2.

Figure 5

Figure 5. Live-dead assay with Caco-2 cells. Images 1 h postexposure to nanocapsules and controls. (A) Live control. Cells with no additional components. (B) Dead control. Cells were incubated for 1 h with 10% ethanol. (C) Monomer nanocapsules containing TEGDMA (10 mg). (D) Initiator nanocapsules containing BPO and BHT (1 mg). (E) Quantification of live-dead assay results.

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Figure S2 demonstrates the biocompatibility of the compounds contained within the PU nanocapsules. The compounds chosen for this system were already characterized as GRAS (generally recognized as safe), but a live/dead assay was performed using these materials to see how the viability of the cells in the presence of these compounds compared to the viability of the cells in the presence of the nanocapsules in which these materials are contained. Caco-2 cells were chosen because epithelial cells are the first likely to come into contact with these materials in a dental resin, and they are sensitive to their environment.
Figure 5 depicts the results of the live/dead assay performed using the Caco-2 cell line with nanocapsules containing either the monomer or BPO. The images were taken after the cells had been exposed to the nanocapsules and the various encapsulated materials for 1 h. Live cells, stained by calcein-AM, appear green. Dead cells, stained by ethidium homodimer-1, appear red. Quantification of the results of the live/dead assay can be seen in Figure 5F. These can be compared to the free compounds tested in Figure S2.
Doing a comparison of the monomer nanocapsules and the monomer compound (TEGDMA), one can see that there is a slightly higher viability when cells are exposed to 10 mg of the monomer nanocapsules than when they are exposed to 10 mg of TEGDMA (83% viability in the presence of the monomer nanocapsules (Figure 5) vs 75% in the presence of the TEGDMA (Figure S2)). In contrast, the initiator nanocapsules and the initiator compound (BPO) both displayed comparably high levels of cytotoxicity, with 50% or fewer of the cells living after 1 h of exposure to 10 mg of the initiator nanocapsules or to 10 mg of free BPO. This necessitated using smaller quantities of the materials for live/dead assays. At a quantity of 1 mg, 100% cell viability was seen for both the initiator nanocapsules and BPO. We know from previous work with the nanocapsules that compounds like fluorescein can be within the shell of the nanocapsules, (24) and there is a high probability of that happening in this case such that some of the BPO is not within the core of the nanocapsules but near the surface of the shells.

Discussion

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TEGDMA was chosen as the monomer because it has a long shelf-life yet polymerizes quickly. (25) It is important for the healing liquid to have a relatively low viscosity to flow and fill the cracks of the resin matrix; TEGDMA is able to flow and has previously been used as a dental monomer with acceptable biocompatibility. (12) Additionally, TEGDMA can form a polymer via free-radical initiation by using a peroxide initiator (and a tertiary amine accelerator to speed the reaction). (25)
The novelty of this system lies in the use of all GRAS approved components and the extensive biocompatibility of the self-healing systems created. To stabilize the BPO to ensure free radicals are not formed prior to its release from the capsule, BHT was used. This compound scavenges the free-radical species that are responsible for peroxide formation and acts as an effective suppressor to peroxide formation. (26) The use of BPO and BHT in the initiator component of a dual-capsule-based self-healing system further extends the novelty of the study as well as the likelihood that this system would be stable over time. While over the short term, mixing BPO in the matrix does work to promote self-healing in some of the samples, having a dual-capsule system with BPO mixed with BHT increases the stability of the system.
One of the exciting findings in this work was that the nanocapsules did fracture. For a capsule-based self-healing system to be effective, the capsules must break as a crack propagates through the resin. If the shell is too thick, the capsules will not rupture when a crack propagates; however, if the shell is too thin, the capsules will be too fragile. (27) These capsules are stable and do fracture appropriately. However, only a fraction of the samples exhibited self-healing following fracture. One of the most significant challenges we encountered with the nanocapsule system was obtaining good mixing of nanocapsules so that they were well dispersed in the system. Beyond this, loading the nanocapsules into this matrix was challenging. We were limited to 3 wt % capsules in the matrix. This is in contrast to other work which looked at 5 wt % of particles. (12) Higher loading may be possible in different resin systems. Nonetheless, the healing efficiency with lower concentrations of nanocapsules is still comparable. The 5 wt % system exhibited healing efficiencies on the order of 35%. (12) We achieved efficiencies consistent with this, but of course, only in a fraction of the samples tested. To move this technology into an application, the mixing issue will have to be considered carefully to make this system more reproducible.
The degree of biocompatibility of the self-healing system is worth noting. The majority of studies involving the use of nanocapsules test cell viability in the presence of microgram quantities of a given biomaterial. (28) The results of the live-dead assays presented in this work demonstrate that one can achieve 80% cell viability or greater even when cells are directly exposed to as much as 10 mg of the monomer nanocapsules or 1 mg of the initiator nanocapsules. Given that the capsules only make up 3 wt % of the dog bone samples used in the tensile tests, it is highly unlikely that a quantity greater than 1 mg of the nanocapsules would ever be needed, let alone 10 mg.

Conclusions

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By embedding PU nanocapsules encapsulating TEGDMA in an epoxy resin and comparing these resins to blank resins, the effects the monomer capsules have on the mechanical properties of a resin were determined. Tensile testing was used to determine the properties of both resin systems; the resin without monomer capsules proved to be stronger than the resin with the monomer capsules when the elastic modulus, yield stress, UTS, and strain to fracture in both types of resins were compared. However, it is important to note that the monomer capsules did indeed crack during the resin fracture. This ultimately proved that the capsules have potential to have a self-healing effect in a resin when a crack propagates through the resin. If such a crack were to occur and result in free nanocapsules entering the GI tract, the health of the patient would not be jeopardized, with the results of the live-dead assays demonstrating that a biocompatible self-healing system has been developed. Furthermore, after examining the self-healing capacity of resins with the monomer capsules and unencapsulated BPO and the monomer capsules and initiator capsules, a small degree of self-healing was present within the resins. Further testing must be pursued to fully understand the degree of self-healing possible in this dual-capsule system.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.2c02080.

  • Supplemental information is included in order to better describe the monomer and initiator capsule characteristics in addition to increase the comprehension of the self-healing reaction. Additionally, the supplemental information contains more details from the mechanical tests performed (PDF)

Terms & Conditions

Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

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  • Corresponding Author
  • Authors
    • Sydney Menikheim - Department of Chemical, Biochemical, and Environmental Engineering, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, United States
    • Joshua Leckron - Department of Chemical, Biochemical, and Environmental Engineering, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, United States
    • Michael Duffy - Department of Mechanical Engineering, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, United States
    • Marc Zupan - Department of Mechanical Engineering, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250, United States
    • Amber Mallory - Naval Medical Research Unit SA, 3650 Chambers Pass Bldg #3610, JBSA Fort Sam Houston, Houston, Texas 78234, United States
    • Wen Lien - 59th Medical Wing, Lackland AFB, San Antonio, Texas 78236, United States
  • Author Contributions

    The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. S.M. and J.L. contributed equally.

  • Funding

    Contract from Naval Medical Research Unit, San Antonio. N32398-18-P-0105. This work was supported/funded by work unit number G1801.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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The views expressed in this article reflect the results of research conducted by the author and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense, nor the United States Government. Two of the authors are a military service member or federal/contracted employee of the United States Government. This work was prepared as part of their official duties. Title 17 U.S.C. 105 provides that ‘copyright protection under this title is not available for any work of the United States Government.’ Title 17 U.S.C. 101 defines a U.S. Government work as work prepared by a military service member or employee of the U.S. Government as part of that person’s official duties.

Abbreviations

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PU

polyurethane

GRAS

generally recognized as safe

TEGDMA

triethylene glycol dimethacrylate

BPO

benzoyl peroxide

SDS

sodium dodecyl sulfate

HD

hexadecane

HDOH

1,6-hexanediol

IPDI

isophorone diisocyanate

ASTM

American Society for Testing and Materials

DI

deionized

SEM

scanning electron microscopy

DLS

dynamic light scattering

FT-IR

Fourier-transform infrared spectroscopy

GPC

gel permeation chromatography

NMR

nuclear magnetic resonance

DMSO

dimethyl sulfoxide

THF

tetrahydrofuran

UTS

ultimate tensile strength

PDI

polydispersity index

References

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    Colloid and Polymer Science (2007), 285 (7), 781-791CODEN: CPMSB6; ISSN:0303-402X. (Springer)
    Microcapsules contg. healing agents have been used to develop the self-healing polymeric composites. These microcapsules must possess special properties such as appropriate strength and stability in surrounding medium. A new series of microcapsules contg. dicyclopentadiene (DCPD) with melamine-formaldehyde (MF) resin as shell material were synthesized by in situ polymn. technol. These microcapsules may satisfy the requirements for self-healing polymeric composites. The chem. structure of microcapsule was identified by using Fourier transform IR (FTIR) spectrometer. The morphol. of microcapsule was obsd. by using optical microscope (OM) and scanning electron microscope. Size distribution and mean diam. of microcapsules were detd. with OM. The thermal properties of microcapsules were investigated by using thermogravimetric anal. and differential scanning calorimetry. Addnl., the self-healing efficiency was evaluated. The results indicate that the poly(melamine-formaldehyde) (PMF) microcapsules contg. DCPD have been synthesized successfully, and their mean diams. fall in the range of 65.2-202.0 μm when the adjusting agitation rate varies from 150 to 500 rpm. Increasing the surfactant concn. can decrease the diams. of microcapsules. The prepd. microcapsules are thermally stable up to 69 °. The PMF microcapsules contg. DCPD can be applied to polymeric composites to fabricate the self-healing composites. The self-healing composite was prepd. by mixing bisphenol A epoxy resin with prepd. microcapsules, amine curing agent and catalyst; degassing the mixt., curing in glass mold and making specimens for self-healing expts. where composites with microcapsules of larger diam. showed higher fracture self-healing efficiency.
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  10. 10
    White, S. R.; Sottos, N. R.; Geubelle, P. H.; Moore, J. S.; Kessler, M. R.; Sriram, S. R.; Brown, E. N.; Viswanathan, S. Autonomic healing of polymer composites. Nature 2001, 409, 794– 797,  DOI: 10.1038/35057232
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    10
    Autonomic healing of polymer composites
    White, S. R.; Sottos, N. R.; Geubelle, P. H.; Moore, J. S.; Kessler, M. R.; Sriram, S. R.; Brown, E. N.; Viswanathan, S.
    Nature (London, United Kingdom) (2001), 409 (6822), 794-797CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
    Structural polymers are susceptible to damage in the form of cracks, which form deep within the structure where detection is difficult and repair is almost impossible. Cracking leads to mech. degrdn. of fiber-reinforced polymer composites; in microelectronic polymeric components it can also lead to elec. failure. Microcracking induced by thermal and mech. fatigue is also a long-standing problem in polymer adhesives. Regardless of the application, once cracks have formed within polymeric materials, the integrity of the structure is significantly compromised. Expts. exploring the concept of self-repair have been previously reported, but the only successful crack-healing methods that have been reported so far require some form of manual intervention. Here, a structural polymeric material with the ability to autonomically heal cracks is reported. The material incorporates a microencapsulated healing agent that is released upon crack intrusion. Polymn. of the healing agent is then triggered by contact with an embedded catalyst, bonding the crack faces. The fracture expts. yield as much as 75% recovery in toughness, and the approach may be applicable to other brittle materials systems (including ceramics and glasses).
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  11. 11
    (a) Wertzberger, B. E.; Steere, J. T.; Pfeifer, R. M.; Nensel, M. A.; Latta, M. A.; Gross, S. M. Physical characterization of a self-healing dental restorative material. J. Appl. Polym. Sci. 2010, 118, 428– 434,  DOI: 10.1002/app.31542
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    11a
    Physical characterization of a self-healing dental restorative material
    Wertzberger, Brittany E.; Steere, Joshua T.; Pfeifer, Ryan M.; Nensel, Melissa A.; Latta, Mark A.; Gross, Stephen M.
    Journal of Applied Polymer Science (2010), 118 (1), 428-434CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)
    The objectives of this study were to det. the efficacy of self-healing a highly filled composite and to investigate the phys. properties of a model dental compd. formulated to autonomically heal cracks. A visible light cured model resin consisting of TEGMA : UDMA : BisGMA (1 : 1 : 1) at 45% wt./wt. with silane 0.7 μ glass was formulated with a self-healing system consisting of encapsulated dicyclopentadiene and Grubbs' catalyst. The base resin was also formulated and characterized with the microcapsules alone, Grubbs' catalyst alone, and no healing additives. Fracture toughness (KIc) was assessed using single edge notch specimens in three-point bend (n = 12). Data was analyzed with ANOVA/Tukey's at p ≤ 0.05. DMA was performed from -140 to 250°C at 2°/min and 1 Hz. Storage and loss modulus, Tg and tan δ, was recorded for each material. The self-healing material was loaded to failure, was left to sit for 7 days and then loaded a second time to failure to det. healing in the material. These specimens had a KIc = 0.69 ± 0.072 for a 57% av. recovery rate of the original fracture toughness. The fracture toughness of the self-healing material was statistically similar to the control. The modulus decreased in the composites with encapsulated dicyclopentadiene. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010.
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    (b) Biggs, P.; Jones, L.; Wellborn, B.; Lewis, G. A Self-healing PMMA Bone Cement: Influence of Crystal Size of Grubbs’ Catalyst. In 25th Southern Biomedical Engineering Conference 2009, 15–17 May 2009, Miami, Florida, USA, Berlin, Heidelberg, 2009// , 2009; McGoron, A. J., Li, C.-Z., Lin, W.-C., Eds.; Springer Berlin Heidelberg, 147– 150.
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  12. 12
    Wu, J.; Weir, M. D.; Zhang, Q.; Zhou, C.; Melo, M. A.; Xu, H. H. Novel self-healing dental resin with microcapsules of polymerizable triethylene glycol dimethacrylate and N,N-dihydroxyethyl-p-toluidine. Dent. Mater. 2016, 32, 294– 304,  DOI: 10.1016/j.dental.2015.11.014
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    12
    Novel self-healing dental resin with microcapsules of polymerizable triethylene glycol dimethacrylate and N,N-dihydroxyethyl-p-toluidine
    Wu, Junling; Weir, Michael D.; Zhang, Qiang; Zhou, Chuanjian; Melo, Mary Anne S.; Xu, Hockin H. K.
    Dental Materials (2016), 32 (2), 294-304CODEN: DEMAEP; ISSN:0109-5641. (Elsevier Ltd.)
    Bulk fracture is one of the primary reasons for resin-based dental restoration failures. To date, there has been no report on the use of polymerizable dental monomers with acceptable biocompatibility to develop a resin with substantial self-healing capability. The objectives of this study were to: (1) develop a self-healing resin contg. microcapsules with triethylene glycol dimethacrylate (TEGDMA)-N,N-dihydroxyethyl-p-toluidine (DHEPT) healing liq. in poly(urea-formaldehyde) (PUF) shells for the first time, and (2) det. the phys. and mech. properties, self-healing efficiency, and fibroblast cytotoxicity. Microcapsules of polymerizable TEGDMA-DHEPT in PUF were prepd. via an in situ polymn. method. Microcapsules were added into a BisGMA-TEGDMA resin at microcapsule mass fractions of 0%, 5%, 10%, 15% and 20%. A flexural test was used to measure composite strength and elastic modulus. A single edge V-notched beam method was used to measure fracture toughness KIC and self-healing efficiency. Flexural strength and elastic modulus (mean ± sd; n = 6) of resin contg. 5-15% microcapsules were similar to control without microcapsules (p > 0.1). Adding microcapsules into the resin increased the virgin KIC, which was about 40% higher at 15% microcapsules than that with 0% microcapsules (p < 0.05). Specimens were fractured and healed, then fractured again to measure the healed KIC. A self-healing efficiency of about 65% in KIC recovery was obtained with 10-20% microcapsules. All specimens with 0-20% microcapsules had fibroblast viability similar to control without resin eluents (p > 0.1). Self-healing dental resin contg. microcapsules with polymerizable TEGDMA-DHEPT healing liq. in PUF shells were prepd. for the first time with excellent self-healing capability. These microcapsules and self-healing resins contg. them may be promising for dental restorations to heal cracks/damage and increase durability.
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  13. 13
    Caruso, M. M.; Delafuente, D. A.; Ho, V.; Sottos, N. R.; Moore, J. S.; White, S. R. Solvent-Promoted Self-Healing Epoxy Materials. Macromolecules 2007, 40, 8830– 8832,  DOI: 10.1021/ma701992z
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    13
    Solvent-Promoted Self-Healing Epoxy Materials
    Caruso, Mary M.; Delafuente, David A.; Ho, Victor; Sottos, Nancy R.; Moore, Jeffrey S.; White, Scott R.
    Macromolecules (Washington, DC, United States) (2007), 40 (25), 8830-8832CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Our objective in this work is to demonstrate that cracks formed in epoxy-based thermoset materials can autonomically be healed with org. solvents, preventing further crack propagation, while recovering the material's original mech. integrity.
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  14. 14
    Dailey, M. M. C.; Silvia, A. W.; McIntire, P. J.; Wilson, G. O.; Moore, J. S.; White, S. R. A self-healing biomaterial based on free-radical polymerization. J. Biomed. Mater. Res. A 2014, 102, 3024– 3032,  DOI: 10.1002/jbm.a.34975
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    14
    A self-healing biomaterial based on free-radical polymerization
    Dailey, Mary M. Caruso; Silvia, Alexander W.; McIntire, Patrick J.; Wilson, Gerald O.; Moore, Jeffrey S.; White, Scott R.
    Journal of Biomedical Materials Research, Part A (2014), 102A (9), 3024-3032CODEN: JBMRCH; ISSN:1549-3296. (John Wiley & Sons, Inc.)
    Self-healing chem. used for damage repair have not previously been demonstrated for free-radical polymn. pathways. However, this chem. is important for addn. polymers such as poly(Me methacrylate) used in bone cement and epoxy vinyl ester used in dental resins. Self-healing biomaterials offer the potential for safer and longer lasting implants and restoratives by slowing or arresting crack damage. In the free-radical self-healing system reported here, the three components required for polymn. (free-radical peroxide initiator, tertiary amine activator, and vinyl acrylate monomers) are compartmentalized into two sep. microcapsules-one contg. the peroxide initiator, and the other contg. both monomer and activator. Crack damage ruptures the capsules so that the three components mix and react to form a new polymer that effectively rebonds the crack and restores approx. 75% of the original fracture toughness. Optimal healing is obtained by a systematic evaluation of the effect of monomer, initiator, and activator concn. on healing performance.
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  15. 15
    Brochu, A. B. W.; Matthys, O. B.; Craig, S. L.; Reichert, W. M. Extended fatigue life of a catalyst free self-healing acrylic bone cement using microencapsulated 2-octyl cyanoacrylate. J. Biomed. Mater. Res. B Appl. Biomater. 2015, 103, 305– 312,  DOI: 10.1002/jbm.b.33199
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    15
    Extended fatigue life of a catalyst free self-healing acrylic bone cement using microencapsulated 2-octyl cyanoacrylate
    Brochu, Alice B. W.; Matthys, Oriane B.; Craig, Stephen L.; Reichert, William M.
    Journal of Biomedical Materials Research, Part B: Applied Biomaterials (2015), 103B (2), 305-312CODEN: JBMRGL; ISSN:1552-4973. (John Wiley & Sons, Inc.)
    The tissue adhesive 2-octyl cyanoacrylate (OCA) was encapsulated in polyurethane microshells and incorporated into bone cement to form a catalyst free, self-healing bone cement comprised of all clin. approved components. The bending strength, modulus, and fatigue lifetime were investigated in accordance with ASTM and ISO stds. for the testing of PMMA bone cement. The bending strength of bone cement specimens decreased with increasing wt % capsules content for capsules without or with OCA, with specimens of <5 wt % capsule content showing minimal effect. In contrast, bone cement bending modulus was insensitive to capsule content. Load controlled fatigue testing was performed in air at room temp. on capsule free bone cement (0 wt %), bone cement with 5 wt % OCA-free capsules (5 wt % No OCA), and 5 wt % OCA-contg. capsules (5 wt % OCA). Specimens were tested at a frequency of 5 Hz at max. stresses of 90%, 80%, 70%, and 50% of each specimen's bending strength until failure. The 5 wt % OCA exhibited significant self-healing at 70% and 50% of its ref. strength (p < 0.05). Fatigue testing of all three specimen types in air at 22 MPa (50% of ref. strength of the 5 wt % OCA specimens) showed that the cycles to failure of OCA-contg. specimens was increased by two-fold compared with the OCA-free and capsule-free specimens. This study represents the first demonstration of dynamic, catalyst free self-healing in a biomaterial formulation. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 103B: 305-312, 2015.
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  16. 16
    Gladman, A. S.; Celestine, A.-D. N.; Sottos, N. R.; White, S. R. Autonomic healing of acrylic bone cement. Adv. Healthc. Mater. 2015, 4, 202– 207,  DOI: 10.1002/adhm.201400084
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    16
    Autonomic Healing of Acrylic Bone Cement
    Gladman, A. Sydney; Celestine, Asha-Dee N.; Sottos, Nancy R.; White, Scott R.
    Advanced Healthcare Materials (2015), 4 (2), 202-207CODEN: AHMDBJ; ISSN:2192-2640. (Wiley-VCH Verlag GmbH & Co. KGaA)
    This study demonstrated a microencapsulated self-healing system in Simplex P bone cement using a non-toxic solvent approach. Healing efficiencies up to 0.80 were achieved under quasi-static fracture and the incorporation of microcapsules did not reduce the inherent fracture toughness of the cement. Solvents were screened for use in self-healing system based on compatibility with established encapsulation procedures, low toxicity, and their ability to solvent weld PMMA. Thermogravimetric anal. (TGA) scans showed microcapsule's excellent thermal stability with little mass lost up to 200. Morphol. differences in fracture surfaces between different healing systems and conditions are revealed in the SEM images.
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  17. 17
    Santerre, J. P.; Woodhouse, K.; Laroche, G.; Labow, R. S. Understanding the biodegradation of polyurethanes: From classical implants to tissue engineering materials. Biomaterials 2005, 26, 7457– 7470,  DOI: 10.1016/j.biomaterials.2005.05.079
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    17
    Understanding the biodegradation of polyurethanes: From classical implants to tissue engineering materials
    Santerre, J. P.; Woodhouse, K.; Laroche, G.; Labow, R. S.
    Biomaterials (2005), 26 (35), 7457-7470CODEN: BIMADU; ISSN:0142-9612. (Elsevier Ltd.)
    A review. After almost half a century of use in the health field, polyurethanes (PUs) remain one of the most popular group of biomaterials applied for medical devices. Their popularity was sustained as a direct result of their segmented block copolymeric character, which endows them with a wide range of versatility in terms of tailoring their phys. properties, blood and tissue compatibility, and more recently their biodegrdn. character. While they became recognized in the 1970s and 1980s as the blood contacting material of choice in a wide range of cardiovascular devices their application in long-term implants fell under scrutiny with the failure of pacemaker leads and breast implant coatings contg. PUs in the late 1980s. During the next decade PUs became extensively researched for their relative sensitivity to biodegrdn. and the desire to further understand the biol. mechanisms for in vivo biodegrdn. The advent of mol. biol. into mainstream biomedical engineering permitted the probing of mol. pathways leading to the biodegrdn. of these materials. Knowledge gained throughout the 1990s has not only yielded novel PUs that contribute to the enhancement of biostability for in vivo long-term applications, but was also translated to form a new class of bioresorbable materials with all the versatility of PUs in terms of phys. properties but now with a more integrative nature in terms of biocompatibility. The current review will briefly survey the literature, which initially identified the problem of PU degrdn. in vivo and the subsequent studies that have led to the field's further understanding of the biol. processes mediating the breakdown. An overview of research emerging on PUs sought for use in combination (drug+polymer) products and tissue regeneration applications will then be presented.
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  18. 18
    Srinivasan, P. K.; Sperber, V.; Afify, M.; Tanaka, H.; Fukushima, K.; Kögel, B.; Gremse, F.; Tolba, R. Novel synthetic adhesive as an effective alternative to Fibrin based adhesives. World J. Hepatol. 2017, 9, 1030– 1039,  DOI: 10.4254/wjh.v9.i24.1030
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    18
    Novel synthetic adhesive as an effective alternative to Fibrin based adhesives
    Srinivasan Pramod Kadaba; Sperber Vera; Afify Mamdouh; Tanaka Hirokazu; Fukushima Kenji; Kogel Babette; Tolba Rene; Gremse Felix
    World journal of hepatology (2017), 9 (24), 1030-1039 ISSN:1948-5182.
    AIM: To compare a novel, fully synthetic, polyurethane based glue (MAR-1) to fibrin sealant in a partial liver resection rat model. METHODS: After 50% resection of the lateral left liver lobe in male Wistar rats (n = 7/group/time point), MAR-1, Fibrin or NaCl was applied. After 14, 21 and 90 postoperative days, sealant degradation, intra-abdominal adhesions were scored, and histological examination of liver tissue was performed. RESULTS: (Mean ± SEM) (MAR-1 vs Fibrin vs NaCl). Bleeding mass was significantly higher in NaCl (3.36 ± 0.51 g) compared to MAR-1 (1.44 ± 0.40 g) and Fibrin (1.16 ± 0.32 g). At 14 and 90 d, bleeding time was significantly lower in MAR-1 (6.00 ± 0.9 s; 13.57 ± 3.22 s) and Fibrin (3.00 ± 0.44 s; 22.2 ± 9.75 s) compared to NaCl (158.16 ± 11.36 s; 127.5 ± 23.3 s). ALT levels were significantly higher in MAR-1 (27.66 ± 1 U/L) compared to Fibrin (24.16 ± 0.98 U/L) and NaCl (23.85 ± 0.80 U/L). Intrabdominal adhesions were significantly lower in MAR-1 (11.22% ± 5.5%) compared to NaCl (58.57% ± 11.83%). Degradation of the glue was observed and MAR-1 showed almost no traces of glue in the abdominal cavity as compared to the Fibrin (10% ± 5% 14 d; 7% ± 3% 21 d). Survival showed no significant differences between the groups. CONCLUSION: Compared to Fibrin, MAR-1 showed similar hemostatic properties, no adverse effects, and is biocompatible. Further studies on adhesion strength and biodegradability of synthetic sealants are warranted.
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  19. 19
    Lee, C. The Mechanical Properties of PMMA Bone Cement. In The Well-Cemented Total Hip Arthroplasty: Theory and Practice; Springer: Berlin Heidelberg, 2005; 60– 66.
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  20. 20
    Torini, L.; Argillier, J. F.; Zydowicz, N. Interfacial Polycondensation Encapsulation in Miniemulsion. Macromolecules 2005, 38, 3225– 3236,  DOI: 10.1021/ma047808e
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    20
    Interfacial polycondensation encapsulation in miniemulsion
    Torini, L.; Argillier, J. F.; Zydowicz, N.
    Macromolecules (2005), 38 (8), 3225-3236CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
    Oily core polyurethane nanocapsules with a mean diam. of 200 nm were formulated in miniemulsion by interfacial polycondensation. The encapsulation process in miniemulsion was optimized by the choice of the surfactant type (anionic, cationic, or nonionic) and concn.; hexadecane was the costabilizer. Size distribution was studied by dynamic laser light scattering, and ζ potential was also detd. The size distribution appeared relatively narrow. Scanning and TEM expts. attested for the submicrometer size, the spherical shape of the capsules, and a smooth external wall. The thermal properties of the polyurethane wall were detd. by DSC and TGA, with a fusion temp. around 40 °C, suggesting the presence of defaults in the macromol. backbone such as irregular bounds of urethane and urea functions. The chem. structure of the polymer wall was studied by 13C NMR and MALDI-TOF mass spectrometry. Both methods attested for the presence of urethane and urea units in the macromol. chain. MALDI-TOF expts. allowed the study of the microstructure of the polymer wall and proved the presence of urethane and urea homopolymer and urethane-urea copolymer. Although the detn. of the mol. wt. was not possible because of the high polydispersity of the sample, the mass range was comprised between 500 and 3000 Da, in accordance with the no.-av. mol. wt. detd. by size exclusion chromatog. (PS stds.).
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  21. 21
    Guo, J.; Pan, Q.; Huang, C.; Zhao, Y.; Ouyang, X.; Huo, Y.; Duan, S. The role of surfactant and costabilizer in controlling size of nanocapsules containing TEGDMA in miniemulsion. J. Wuhan Univ. Technol.-Mater. Sci. Ed. 2009, 24, 1004– 1006,  DOI: 10.1007/s11595-009-7004-2
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    21
    The role of surfactant and costabilizer in controlling size of nanocapsules containing TEGDMA in miniemulsion
    Guo, Jinxin; Pan, Qiuhua; Huang, Cui; Zhao, Yanbing; Ouyang, Xiaobai; Huo, Yonghong; Duan, Sansan
    Journal of Wuhan University of Technology, Materials Science Edition (2009), 24 (6), 1004-1006CODEN: JWUTE8; ISSN:1000-2413. (Wuhan University of Technology)
    Nanocapsules with triethylene glycol dimethacrylate (TEGDMA) as core material and polyurethane as wall material used for self-healing bonding resin were prepd. by interfacial polycondensation in miniemulsion. The influence of surfactant and costabilizer concn. on nanocapsules size and stability of nanocapsules was investigated. The size and its polydispersity of the nanocapsules were measured by light-scattering particle size analyzer. When the concn. of SDS were increased from 2.5wt% to 10wt%, the size decreases from 340.5 nm to 258.3 nm, PDI decreased from 0.210 to 0.111. As the concn. of HD increased, the size and PDI were both decreased, When reaching 10wt%, the size was 258.0 nm, PDI was 0.130. SDS and HD play important effect in synthesis of Nanocapsules contg. TEGDMA. By changing the surfactant and costabilizer concn. it was possible to synthesize a wide variety of nanocapsules sizes. The performance and tech. parameters of nanocapsules had been researched preliminarily, which built the solid foundation for the application to the self-repairing bonding resin.
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  22. 22
    (a) Kaizer, M. R.; Almeida, J. R.; Goncalves, A. P.; Zhang, Y.; Cava, S. S.; Moraes, R. R. Silica Coating of Nonsilicate Nanoparticles for Resin-Based Composite Materials. J. Dent. Res. 2016, 95, 1394– 1400,  DOI: 10.1177/0022034516662022
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    22a
    Silica coating of nonsilicate nanoparticles for resin-based composite materials
    Kaizer, M. R.; Almeida, J. R.; Goncalves, A. P. R.; Zhang, Y.; Cava, S. S.; Moraes, R. R.
    Journal of Dental Research (2016), 95 (12), 1394-1400CODEN: JDREAF; ISSN:0022-0345. (Sage Publications)
    This study was designed to develop and characterize a silica-coating method for cryst. nonsilicate ceramic nanoparticles (Al2O3, TiO2, and ZrO2). The hypothesis was that the coated nonsilicate nanoparticles would stably reinforce a polymeric matrix due to effective silanation. Silica coating was applied via a sol-gel method, with tetra-Et orthosilicate as a silica precursor, followed by heat treatment. The chem. and microstructural characteristics of the nanopowders were evaluated before and after silica coating through x-ray diffraction, BET (Brunauer-Emmett-Teller), energy-dispersive x-ray spectroscopy, field emission SEM, and transmission electron microscopy analyses. Coated and noncoated nanoparticles were silanated before prepn. of hybrid composites, which contained glass microparticles in addn. to the nanoparticles. The composites were mech. tested in 4-point bending mode after aging (10,000 thermal cycles). Results of all chem. and microstructural analyses confirmed the successful obtaining of silica-coated nanoparticles. Two distinct aspects were obsd. depending on the type of nanoparticle tested: 1) formation of a silica shell on the surface of the particles and 2) nanoparticle clusters embedded into a silica matrix. The aged hybrid composites formulated with the coated nanoparticles showed improved flexural strength (10% to 30% higher) and work of fracture (35% to 40% higher) as compared with composites formulated with noncoated nanoparticles. The tested hypothesis was confirmed: silanated silica-coated nonsilicate nanoparticles yielded stable reinforcement of dimethacrylate polymeric matrix due to effective silanation. The silica-coating method presented here is a versatile and promising novel strategy for the use of cryst. nonsilicate ceramics as a reinforcing phase of polymeric composite biomaterials.
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    (b) Li, L.; Zuo, Y.; Zou, Q.; Yang, B.; Lin, L.; Li, J.; Li, Y. Hierarchical Structure and Mechanical Improvement of an n-HA/GCO-PU Composite Scaffold for Bone Regeneration. ACS Appl. Mater. Interfaces 2015, 7, 22618– 22629,  DOI: 10.1021/acsami.5b07327
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    22b
    Hierarchical Structure and Mechanical Improvement of an Nanohydroxyapatite/Glyceride of Castor Oil-Polyurethane Composite Scaffold for Bone Regeneration
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    ACS Applied Materials & Interfaces (2015), 7 (40), 22618-22629CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
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  1. Shuaishuai Liu, Tolulope Ale, Victor Kehinde, Temitope Ale, Heuy-Ching Wang, Erin Lavik. Polyester Nanoparticles and Polyurethane Nanocapsules Deliver Pirfenidone To Reduce Fibrosis and Scarring. ACS Biomaterials Science & Engineering 2023, 9 (6) , 3348-3355. https://doi.org/10.1021/acsbiomaterials.3c00087
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  • Abstract

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    Figure 1

    Figure 1. (A) DLS of TEGDMA nanocapsules. (B) Diameter of nanocapsules was consistent batch to batch. (C, D) TEM images of nanocapsules. (E) FT-IR demonstrating the presence of the PU as well as the TEGDMA. (F) SEM showing the nanocapsules (tan arrows) and residual TEGDMA. Not all of the TEGDMA was encapsulated in this formulation.

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    Figure 2

    Figure 2. Incorporating nanocapsules into the matrix. (A) Stress–strain curves for the epoxy resin without nanocapsules (n = 12). (B) Stress–strain curves for samples with nanocapsules (n = 12). (C) Table comparing critical features from these two groups. Adding nanocapsules impacts the mechanical properties of the resin, as expected.

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    Figure 3

    Figure 3. Images show the fracture surface on samples of West System epoxy resin. (A) This image shows the area at which the fracture occurred in a sample without monomer capsules. (B) This SEM image presents a zoomed in image of another fracture site in the resin. (C) This SEM image shows the fracture surface from a sample with monomer capsules. The capsules, especially larger capsules, are evident in the surface and cause a rougher surface. (D) These SEM images show fracture surfaces another sample with monomer capsules at a higher magnification. In these images, it is evident that some of the larger capsules have cracked. The white dots in these images are the nanocapsules. (E, F) These SEM images focus on the monomer capsules in the resin. These images show fractured capsules in the resin.

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    Figure 4

    Figure 4. (A) This figure depicts the stress/strain curves from two of the four samples of resin with the monomer capsules and BPO after self-healing. These samples were prepared at the same time and with the same conditions. The properties of the original resins (R1 and R2) are also displayed for comparative purposes. (B) Stress–strain curves from 2 of the six samples of resin with the monomer capsules and initiator capsules after self-healing. These samples were prepared at the same time and with the same conditions. The properties of the original resins (R4 and R5) are also displayed for comparative purposes. (C) Mechanical properties of R1 and R2, which exhibited self-healing as made and after the self-healing reaction. (D) Mechanical properties of the dual-capsule system as made and after self-healing for the two samples of six that exhibited self-healing.

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    Figure 5

    Figure 5. Live-dead assay with Caco-2 cells. Images 1 h postexposure to nanocapsules and controls. (A) Live control. Cells with no additional components. (B) Dead control. Cells were incubated for 1 h with 10% ethanol. (C) Monomer nanocapsules containing TEGDMA (10 mg). (D) Initiator nanocapsules containing BPO and BHT (1 mg). (E) Quantification of live-dead assay results.

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      Wooley, P. H.; Schwarz, E. M.
      Gene Therapy (2004), 11 (4), 402-407CODEN: GETHEC; ISSN:0969-7128. (Nature Publishing Group)
      A review. Although total joint replacement surgery is one of the most successful clin. procedures performed today, bone loss around knee and hip implants (osteolysis), resulting in aseptic loosening of the prosthesis, remains a major problem for many patients. Over the last decade much has been learned about this process, which is caused by wear debris particles that simulate a local inflammatory response and osteoclastic bone resorption. Aseptic loosening cannot be prevented or treated by existing nonsurgical methods. Gene transfer, however, offers novel possibilities. Here, we review the current state of the field and the exptl. gene therapy approaches that have been investigated toward a soln. to aseptic loosening of prosthetic implants.
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    4. 4
      Apostu, D.; Lucaciu, O.; Berce, C.; Lucaciu, D.; Cosma, D. Current methods of preventing aseptic loosening and improving osseointegration of titanium implants in cementless total hip arthroplasty: a review. J. Int. Med. Res. 2018, 46, 2104– 2119,  DOI: 10.1177/0300060517732697
      4
      Current methods of preventing aseptic loosening and improving osseointegration of titanium implants in cementless total hip arthroplasty: a review
      Apostu, Dragos; Lucaciu, Ondine; Berce, Cristian; Lucaciu, Dan; Cosma, Dan
      Journal of International Medical Research (2018), 46 (6), 2104-2119CODEN: JIMRBV; ISSN:0300-0605. (Sage Publications Ltd.)
      A review. Hip osteoarthritis is the most common joint disorder, and is represented by a degenerative process, resulting in pain and functional impairment. If conservative treatment for hip osteoarthritis fails, the only remaining option is hip arthroplasty. Despite good survival of implants, loosening of components is the most common complication. This leads to revision surgeries, which are tech. demanding, expensive, and result in a low satisfaction rate. Uncemented hip replacements require proper osseointegration for increased survival. Phys. characteristics of implants include biocompatibility, Youngs modulus of elasticity, strength, and corrosion resistance, and each influence fixation of implants. Moreover, implant surface treatments, pore size, pore d., and femoral stem design should be appropriately selected. Patients optimization of obesity, osteoporosis, cardiovascular disease, psychotic disorders, and smoking cessation are assocd. with a higher survival of implants. Surgical factors, such as approach, drilling and rasping, acetabular bone coverage, acetabular cup positioning, and implant size, also affect survival of implants. Avoiding drugs, which may impair osseointegration of implants, and having an appropriate rehabilitation protocol are important. Future directions include anabolic and anti-catabolic bone-acting drugs to enhance osseointegration of implants. Comprehensive knowledge of the factors mentioned above is important for preventing aseptic loosening, with important socioeconomic consequences.
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    5. 5
      Dental Diseases and Oral Health, Organization, W. H., 2003. http://www.who.int/oral_health/publications/en/orh_fact_sheet.pdf (accessed April 28, 2018).
      There is no corresponding record for this reference.
    6. 6
      Petersen, P. E.; Bourgeois, D.; Ogawa, H.; Estupinan-Day, S.; Ndiaye, C. The global burden of oral diseases and risks to oral health. Bull. World Health Organ. 2005, 83, 661– 669
      6
      The global burden of oral diseases and risks to oral health
      Petersen Poul Erik; Bourgeois Denis; Ogawa Hiroshi; Estupinan-Day Saskia; Ndiaye Charlotte
      Bulletin of the World Health Organization (2005), 83 (9), 661-9 ISSN:0042-9686.
      This paper outlines the burden of oral diseases worldwide and describes the influence of major sociobehavioural risk factors in oral health. Despite great improvements in the oral health of populations in several countries, global problems still persist. The burden of oral disease is particularly high for the disadvantaged and poor population groups in both developing and developed countries. Oral diseases such as dental caries, periodontal disease, tooth loss, oral mucosal lesions and oropharyngeal cancers, human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS)-related oral disease and orodental trauma are major public health problems worldwide and poor oral health has a profound effect on general health and quality of life. The diversity in oral disease patterns and development trends across countries and regions reflects distinct risk profiles and the establishment of preventive oral health care programmes. The important role of sociobehavioural and environmental factors in oral health and disease has been shown in a large number of socioepidemiological surveys. In addition to poor living conditions, the major risk factors relate to unhealthy lifestyles (i.e. poor diet, nutrition and oral hygiene and use of tobacco and alcohol), and limited availability and accessibility of oral health services. Several oral diseases are linked to noncommunicable chronic diseases primarily because of common risk factors. Moreover, general diseases often have oral manifestations (e.g. diabetes or HIV/AIDS). Worldwide strengthening of public health programmes through the implementation of effective measures for the prevention of oral disease and promotion of oral health is urgently needed. The challenges of improving oral health are particularly great in developing countries.
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    7. 7
      Manhart, J.; Chen, H.; Hamm, G.; Hickel, R. Buonocore Memorial Lecture. Review of the clinical survival of direct and indirect restorations in posterior teeth of the permanent dentition. Oper. Dent. 2004, 29, 481– 508
      7
      Buonocore Memorial Lecture. Review of the clinical survival of direct and indirect restorations in posterior teeth of the permanent dentition
      Manhart Juergen; Chen Hongyan; Hamm Gerald; Hickel Reinhard
      Operative dentistry (2004), 29 (5), 481-508 ISSN:0361-7734.
      This review provides a survey on the longevity of restorations in stress-bearing posterior cavities and assesses possible reasons for clinical failure. The dental literature, predominantly since 1990, was reviewed for longitudinal, controlled clinical studies and retrospective cross-sectional studies of posterior restorations. Only studies investigating the clinical performance of restorations in permanent teeth were included. Longevity and annual failure rates of amalgam, direct composite restorations, compomers, glass ionomers and derivative products, composite and ceramic inlays and cast gold restorations were determined for Class I and II cavities. Mean (SD) annual failure rates in posterior stress-bearing cavities are: 3.0% (1.9) for amalgam restorations, 2.2% (2.0) for direct composites, 3.6% (4.2) for direct composites with inserts, 1.1% (1.2) for compomer restorations, 7.2% (5.6) for regular glass ionomer restorations, 7.1% (2.8) for tunnel glass ionomers, 6.0% (4.6) for ART glass ionomers, 2.9% (2.6) for composite inlays, 1.9% (1.8) for ceramic restorations, 1.7% (1.6) for CAD/CAM ceramic restorations and 1.4% (1.4) for cast gold inlays and onlays. Publications from 1990 forward showed better results. Indirect restorations exhibited a significantly lower mean annual failure rate than direct techniques (p=0.0031). Longevity of dental restorations is dependent upon many different factors, including material, patient- and dentist-related. Principal reasons for failure were secondary caries, fracture, marginal deficiencies, wear and postoperative sensitivity. We need to learn to distinguish between reasons that cause early failures and those that are responsible for restoration loss after several years of service.
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    8. 8
      (a) Fugolin, A. P. P.; Pfeifer, C. S. New Resins for Dental Composites. J. Dent. Res. 2017, 96, 1085– 1091,  DOI: 10.1177/0022034517720658
      8a
      New Resins for Dental Composites
      Fugolin, A. P. P.; Pfeifer, C. S.
      Journal of Dental Research (2017), 96 (10), 1085-1091CODEN: JDREAF; ISSN:0022-0345. (Sage Publications)
      A review. Restorative composites have evolved significantly since they were first introduced in the early 1960s, with most of the development concg. on the filler technol. This has led to improved mech. properties, notably wear resistance, and has expanded the use of composites to larger posterior restorations. On the org. matrix side, concerns over the polymn. stress and the potential damage to the bonded interface have dominated research in the past 20 y, with many "low-shrinkage" composites being launched com. The lack of clin. correlation between the use of these materials and improved restoration outcomes has shifted the focus more recently to improving materials' resistance to degrdn. in the oral environment, caused by aq. solvents and salivary enzymes, as well as biofilm development. Antimicrobial and ester-free monomers have been developed in the recent past, and evidence is mounting for their potential benefit. This article reviews literature on the newest materials currently on the market and provides an outlook for the future developments needed to improve restoration longevity past the av. 10 y.
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      (b) Kenny, S. M.; Buggy, M. Bone cements and fillers: A review. J. Mater. Sci.: Mater. Med. 2003, 14, 923– 938,  DOI: 10.1023/A:1026394530192
      8b
      Bone cements and fillers: a review
      Kenny, S. M.; Buggy, M.
      Journal of Materials Science: Materials in Medicine (2003), 14 (11), 923-938CODEN: JSMMEL; ISSN:0957-4530. (Kluwer Academic Publishers)
      A review and discussion. J. Charnley (1960) developed the first bone cement in the 1960s using poly(Me methacrylate) (PMMA), which remains the most widely used material for fixation of orthopedic joint replacements. In the field of dentistry, zinc polycarboxylate and glass polyalkenoate cements received major research interest from the 1970s to the present day. The discovery of a well-integrated intermediate layer between bone and many bioactive ceramic phases from the calcium-phosphate system, such as hydroxyapatite (HA), resulted in the development of new cements incorporating such phases. These investigations ranged from the development of castable bioactive materials to modified bioactive composites. This paper attempts to give a broad overview of the many different types of cements that have being developed in the past and those which are being researched at the present time. It has lead to a set of fundamental design criteria that should be considered prior to the development of a cement for use as a bone cement or in applications requiring a bone substitute.
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    9. 9
      Yuan, L.; Liang, G.-Z.; Xie, J.-Q.; He, S.-B. Synthesis and characterization of microencapsulated dicyclopentadiene with melamine–formaldehyde resins. Colloid Polym. Sci. 2007, 285, 781– 791,  DOI: 10.1007/s00396-006-1621-5
      9
      Synthesis and characterization of microencapsulated dicyclopentadiene with melamine-formaldehyde resins
      Yuan, Li; Liang, Guo-Zheng; Xie, Jian-Qiang; He, Shao-Bo
      Colloid and Polymer Science (2007), 285 (7), 781-791CODEN: CPMSB6; ISSN:0303-402X. (Springer)
      Microcapsules contg. healing agents have been used to develop the self-healing polymeric composites. These microcapsules must possess special properties such as appropriate strength and stability in surrounding medium. A new series of microcapsules contg. dicyclopentadiene (DCPD) with melamine-formaldehyde (MF) resin as shell material were synthesized by in situ polymn. technol. These microcapsules may satisfy the requirements for self-healing polymeric composites. The chem. structure of microcapsule was identified by using Fourier transform IR (FTIR) spectrometer. The morphol. of microcapsule was obsd. by using optical microscope (OM) and scanning electron microscope. Size distribution and mean diam. of microcapsules were detd. with OM. The thermal properties of microcapsules were investigated by using thermogravimetric anal. and differential scanning calorimetry. Addnl., the self-healing efficiency was evaluated. The results indicate that the poly(melamine-formaldehyde) (PMF) microcapsules contg. DCPD have been synthesized successfully, and their mean diams. fall in the range of 65.2-202.0 μm when the adjusting agitation rate varies from 150 to 500 rpm. Increasing the surfactant concn. can decrease the diams. of microcapsules. The prepd. microcapsules are thermally stable up to 69 °. The PMF microcapsules contg. DCPD can be applied to polymeric composites to fabricate the self-healing composites. The self-healing composite was prepd. by mixing bisphenol A epoxy resin with prepd. microcapsules, amine curing agent and catalyst; degassing the mixt., curing in glass mold and making specimens for self-healing expts. where composites with microcapsules of larger diam. showed higher fracture self-healing efficiency.
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    10. 10
      White, S. R.; Sottos, N. R.; Geubelle, P. H.; Moore, J. S.; Kessler, M. R.; Sriram, S. R.; Brown, E. N.; Viswanathan, S. Autonomic healing of polymer composites. Nature 2001, 409, 794– 797,  DOI: 10.1038/35057232
      10
      Autonomic healing of polymer composites
      White, S. R.; Sottos, N. R.; Geubelle, P. H.; Moore, J. S.; Kessler, M. R.; Sriram, S. R.; Brown, E. N.; Viswanathan, S.
      Nature (London, United Kingdom) (2001), 409 (6822), 794-797CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      Structural polymers are susceptible to damage in the form of cracks, which form deep within the structure where detection is difficult and repair is almost impossible. Cracking leads to mech. degrdn. of fiber-reinforced polymer composites; in microelectronic polymeric components it can also lead to elec. failure. Microcracking induced by thermal and mech. fatigue is also a long-standing problem in polymer adhesives. Regardless of the application, once cracks have formed within polymeric materials, the integrity of the structure is significantly compromised. Expts. exploring the concept of self-repair have been previously reported, but the only successful crack-healing methods that have been reported so far require some form of manual intervention. Here, a structural polymeric material with the ability to autonomically heal cracks is reported. The material incorporates a microencapsulated healing agent that is released upon crack intrusion. Polymn. of the healing agent is then triggered by contact with an embedded catalyst, bonding the crack faces. The fracture expts. yield as much as 75% recovery in toughness, and the approach may be applicable to other brittle materials systems (including ceramics and glasses).
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    11. 11
      (a) Wertzberger, B. E.; Steere, J. T.; Pfeifer, R. M.; Nensel, M. A.; Latta, M. A.; Gross, S. M. Physical characterization of a self-healing dental restorative material. J. Appl. Polym. Sci. 2010, 118, 428– 434,  DOI: 10.1002/app.31542
      11a
      Physical characterization of a self-healing dental restorative material
      Wertzberger, Brittany E.; Steere, Joshua T.; Pfeifer, Ryan M.; Nensel, Melissa A.; Latta, Mark A.; Gross, Stephen M.
      Journal of Applied Polymer Science (2010), 118 (1), 428-434CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)
      The objectives of this study were to det. the efficacy of self-healing a highly filled composite and to investigate the phys. properties of a model dental compd. formulated to autonomically heal cracks. A visible light cured model resin consisting of TEGMA : UDMA : BisGMA (1 : 1 : 1) at 45% wt./wt. with silane 0.7 μ glass was formulated with a self-healing system consisting of encapsulated dicyclopentadiene and Grubbs' catalyst. The base resin was also formulated and characterized with the microcapsules alone, Grubbs' catalyst alone, and no healing additives. Fracture toughness (KIc) was assessed using single edge notch specimens in three-point bend (n = 12). Data was analyzed with ANOVA/Tukey's at p ≤ 0.05. DMA was performed from -140 to 250°C at 2°/min and 1 Hz. Storage and loss modulus, Tg and tan δ, was recorded for each material. The self-healing material was loaded to failure, was left to sit for 7 days and then loaded a second time to failure to det. healing in the material. These specimens had a KIc = 0.69 ± 0.072 for a 57% av. recovery rate of the original fracture toughness. The fracture toughness of the self-healing material was statistically similar to the control. The modulus decreased in the composites with encapsulated dicyclopentadiene. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010.
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      (b) Biggs, P.; Jones, L.; Wellborn, B.; Lewis, G. A Self-healing PMMA Bone Cement: Influence of Crystal Size of Grubbs’ Catalyst. In 25th Southern Biomedical Engineering Conference 2009, 15–17 May 2009, Miami, Florida, USA, Berlin, Heidelberg, 2009// , 2009; McGoron, A. J., Li, C.-Z., Lin, W.-C., Eds.; Springer Berlin Heidelberg, 147– 150.
      There is no corresponding record for this reference.
    12. 12
      Wu, J.; Weir, M. D.; Zhang, Q.; Zhou, C.; Melo, M. A.; Xu, H. H. Novel self-healing dental resin with microcapsules of polymerizable triethylene glycol dimethacrylate and N,N-dihydroxyethyl-p-toluidine. Dent. Mater. 2016, 32, 294– 304,  DOI: 10.1016/j.dental.2015.11.014
      12
      Novel self-healing dental resin with microcapsules of polymerizable triethylene glycol dimethacrylate and N,N-dihydroxyethyl-p-toluidine
      Wu, Junling; Weir, Michael D.; Zhang, Qiang; Zhou, Chuanjian; Melo, Mary Anne S.; Xu, Hockin H. K.
      Dental Materials (2016), 32 (2), 294-304CODEN: DEMAEP; ISSN:0109-5641. (Elsevier Ltd.)
      Bulk fracture is one of the primary reasons for resin-based dental restoration failures. To date, there has been no report on the use of polymerizable dental monomers with acceptable biocompatibility to develop a resin with substantial self-healing capability. The objectives of this study were to: (1) develop a self-healing resin contg. microcapsules with triethylene glycol dimethacrylate (TEGDMA)-N,N-dihydroxyethyl-p-toluidine (DHEPT) healing liq. in poly(urea-formaldehyde) (PUF) shells for the first time, and (2) det. the phys. and mech. properties, self-healing efficiency, and fibroblast cytotoxicity. Microcapsules of polymerizable TEGDMA-DHEPT in PUF were prepd. via an in situ polymn. method. Microcapsules were added into a BisGMA-TEGDMA resin at microcapsule mass fractions of 0%, 5%, 10%, 15% and 20%. A flexural test was used to measure composite strength and elastic modulus. A single edge V-notched beam method was used to measure fracture toughness KIC and self-healing efficiency. Flexural strength and elastic modulus (mean ± sd; n = 6) of resin contg. 5-15% microcapsules were similar to control without microcapsules (p > 0.1). Adding microcapsules into the resin increased the virgin KIC, which was about 40% higher at 15% microcapsules than that with 0% microcapsules (p < 0.05). Specimens were fractured and healed, then fractured again to measure the healed KIC. A self-healing efficiency of about 65% in KIC recovery was obtained with 10-20% microcapsules. All specimens with 0-20% microcapsules had fibroblast viability similar to control without resin eluents (p > 0.1). Self-healing dental resin contg. microcapsules with polymerizable TEGDMA-DHEPT healing liq. in PUF shells were prepd. for the first time with excellent self-healing capability. These microcapsules and self-healing resins contg. them may be promising for dental restorations to heal cracks/damage and increase durability.
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    13. 13
      Caruso, M. M.; Delafuente, D. A.; Ho, V.; Sottos, N. R.; Moore, J. S.; White, S. R. Solvent-Promoted Self-Healing Epoxy Materials. Macromolecules 2007, 40, 8830– 8832,  DOI: 10.1021/ma701992z
      13
      Solvent-Promoted Self-Healing Epoxy Materials
      Caruso, Mary M.; Delafuente, David A.; Ho, Victor; Sottos, Nancy R.; Moore, Jeffrey S.; White, Scott R.
      Macromolecules (Washington, DC, United States) (2007), 40 (25), 8830-8832CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Our objective in this work is to demonstrate that cracks formed in epoxy-based thermoset materials can autonomically be healed with org. solvents, preventing further crack propagation, while recovering the material's original mech. integrity.
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    14. 14
      Dailey, M. M. C.; Silvia, A. W.; McIntire, P. J.; Wilson, G. O.; Moore, J. S.; White, S. R. A self-healing biomaterial based on free-radical polymerization. J. Biomed. Mater. Res. A 2014, 102, 3024– 3032,  DOI: 10.1002/jbm.a.34975
      14
      A self-healing biomaterial based on free-radical polymerization
      Dailey, Mary M. Caruso; Silvia, Alexander W.; McIntire, Patrick J.; Wilson, Gerald O.; Moore, Jeffrey S.; White, Scott R.
      Journal of Biomedical Materials Research, Part A (2014), 102A (9), 3024-3032CODEN: JBMRCH; ISSN:1549-3296. (John Wiley & Sons, Inc.)
      Self-healing chem. used for damage repair have not previously been demonstrated for free-radical polymn. pathways. However, this chem. is important for addn. polymers such as poly(Me methacrylate) used in bone cement and epoxy vinyl ester used in dental resins. Self-healing biomaterials offer the potential for safer and longer lasting implants and restoratives by slowing or arresting crack damage. In the free-radical self-healing system reported here, the three components required for polymn. (free-radical peroxide initiator, tertiary amine activator, and vinyl acrylate monomers) are compartmentalized into two sep. microcapsules-one contg. the peroxide initiator, and the other contg. both monomer and activator. Crack damage ruptures the capsules so that the three components mix and react to form a new polymer that effectively rebonds the crack and restores approx. 75% of the original fracture toughness. Optimal healing is obtained by a systematic evaluation of the effect of monomer, initiator, and activator concn. on healing performance.
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    15. 15
      Brochu, A. B. W.; Matthys, O. B.; Craig, S. L.; Reichert, W. M. Extended fatigue life of a catalyst free self-healing acrylic bone cement using microencapsulated 2-octyl cyanoacrylate. J. Biomed. Mater. Res. B Appl. Biomater. 2015, 103, 305– 312,  DOI: 10.1002/jbm.b.33199
      15
      Extended fatigue life of a catalyst free self-healing acrylic bone cement using microencapsulated 2-octyl cyanoacrylate
      Brochu, Alice B. W.; Matthys, Oriane B.; Craig, Stephen L.; Reichert, William M.
      Journal of Biomedical Materials Research, Part B: Applied Biomaterials (2015), 103B (2), 305-312CODEN: JBMRGL; ISSN:1552-4973. (John Wiley & Sons, Inc.)
      The tissue adhesive 2-octyl cyanoacrylate (OCA) was encapsulated in polyurethane microshells and incorporated into bone cement to form a catalyst free, self-healing bone cement comprised of all clin. approved components. The bending strength, modulus, and fatigue lifetime were investigated in accordance with ASTM and ISO stds. for the testing of PMMA bone cement. The bending strength of bone cement specimens decreased with increasing wt % capsules content for capsules without or with OCA, with specimens of <5 wt % capsule content showing minimal effect. In contrast, bone cement bending modulus was insensitive to capsule content. Load controlled fatigue testing was performed in air at room temp. on capsule free bone cement (0 wt %), bone cement with 5 wt % OCA-free capsules (5 wt % No OCA), and 5 wt % OCA-contg. capsules (5 wt % OCA). Specimens were tested at a frequency of 5 Hz at max. stresses of 90%, 80%, 70%, and 50% of each specimen's bending strength until failure. The 5 wt % OCA exhibited significant self-healing at 70% and 50% of its ref. strength (p < 0.05). Fatigue testing of all three specimen types in air at 22 MPa (50% of ref. strength of the 5 wt % OCA specimens) showed that the cycles to failure of OCA-contg. specimens was increased by two-fold compared with the OCA-free and capsule-free specimens. This study represents the first demonstration of dynamic, catalyst free self-healing in a biomaterial formulation. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 103B: 305-312, 2015.
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    16. 16
      Gladman, A. S.; Celestine, A.-D. N.; Sottos, N. R.; White, S. R. Autonomic healing of acrylic bone cement. Adv. Healthc. Mater. 2015, 4, 202– 207,  DOI: 10.1002/adhm.201400084
      16
      Autonomic Healing of Acrylic Bone Cement
      Gladman, A. Sydney; Celestine, Asha-Dee N.; Sottos, Nancy R.; White, Scott R.
      Advanced Healthcare Materials (2015), 4 (2), 202-207CODEN: AHMDBJ; ISSN:2192-2640. (Wiley-VCH Verlag GmbH & Co. KGaA)
      This study demonstrated a microencapsulated self-healing system in Simplex P bone cement using a non-toxic solvent approach. Healing efficiencies up to 0.80 were achieved under quasi-static fracture and the incorporation of microcapsules did not reduce the inherent fracture toughness of the cement. Solvents were screened for use in self-healing system based on compatibility with established encapsulation procedures, low toxicity, and their ability to solvent weld PMMA. Thermogravimetric anal. (TGA) scans showed microcapsule's excellent thermal stability with little mass lost up to 200. Morphol. differences in fracture surfaces between different healing systems and conditions are revealed in the SEM images.
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    17. 17
      Santerre, J. P.; Woodhouse, K.; Laroche, G.; Labow, R. S. Understanding the biodegradation of polyurethanes: From classical implants to tissue engineering materials. Biomaterials 2005, 26, 7457– 7470,  DOI: 10.1016/j.biomaterials.2005.05.079
      17
      Understanding the biodegradation of polyurethanes: From classical implants to tissue engineering materials
      Santerre, J. P.; Woodhouse, K.; Laroche, G.; Labow, R. S.
      Biomaterials (2005), 26 (35), 7457-7470CODEN: BIMADU; ISSN:0142-9612. (Elsevier Ltd.)
      A review. After almost half a century of use in the health field, polyurethanes (PUs) remain one of the most popular group of biomaterials applied for medical devices. Their popularity was sustained as a direct result of their segmented block copolymeric character, which endows them with a wide range of versatility in terms of tailoring their phys. properties, blood and tissue compatibility, and more recently their biodegrdn. character. While they became recognized in the 1970s and 1980s as the blood contacting material of choice in a wide range of cardiovascular devices their application in long-term implants fell under scrutiny with the failure of pacemaker leads and breast implant coatings contg. PUs in the late 1980s. During the next decade PUs became extensively researched for their relative sensitivity to biodegrdn. and the desire to further understand the biol. mechanisms for in vivo biodegrdn. The advent of mol. biol. into mainstream biomedical engineering permitted the probing of mol. pathways leading to the biodegrdn. of these materials. Knowledge gained throughout the 1990s has not only yielded novel PUs that contribute to the enhancement of biostability for in vivo long-term applications, but was also translated to form a new class of bioresorbable materials with all the versatility of PUs in terms of phys. properties but now with a more integrative nature in terms of biocompatibility. The current review will briefly survey the literature, which initially identified the problem of PU degrdn. in vivo and the subsequent studies that have led to the field's further understanding of the biol. processes mediating the breakdown. An overview of research emerging on PUs sought for use in combination (drug+polymer) products and tissue regeneration applications will then be presented.
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    18. 18
      Srinivasan, P. K.; Sperber, V.; Afify, M.; Tanaka, H.; Fukushima, K.; Kögel, B.; Gremse, F.; Tolba, R. Novel synthetic adhesive as an effective alternative to Fibrin based adhesives. World J. Hepatol. 2017, 9, 1030– 1039,  DOI: 10.4254/wjh.v9.i24.1030
      18
      Novel synthetic adhesive as an effective alternative to Fibrin based adhesives
      Srinivasan Pramod Kadaba; Sperber Vera; Afify Mamdouh; Tanaka Hirokazu; Fukushima Kenji; Kogel Babette; Tolba Rene; Gremse Felix
      World journal of hepatology (2017), 9 (24), 1030-1039 ISSN:1948-5182.
      AIM: To compare a novel, fully synthetic, polyurethane based glue (MAR-1) to fibrin sealant in a partial liver resection rat model. METHODS: After 50% resection of the lateral left liver lobe in male Wistar rats (n = 7/group/time point), MAR-1, Fibrin or NaCl was applied. After 14, 21 and 90 postoperative days, sealant degradation, intra-abdominal adhesions were scored, and histological examination of liver tissue was performed. RESULTS: (Mean ± SEM) (MAR-1 vs Fibrin vs NaCl). Bleeding mass was significantly higher in NaCl (3.36 ± 0.51 g) compared to MAR-1 (1.44 ± 0.40 g) and Fibrin (1.16 ± 0.32 g). At 14 and 90 d, bleeding time was significantly lower in MAR-1 (6.00 ± 0.9 s; 13.57 ± 3.22 s) and Fibrin (3.00 ± 0.44 s; 22.2 ± 9.75 s) compared to NaCl (158.16 ± 11.36 s; 127.5 ± 23.3 s). ALT levels were significantly higher in MAR-1 (27.66 ± 1 U/L) compared to Fibrin (24.16 ± 0.98 U/L) and NaCl (23.85 ± 0.80 U/L). Intrabdominal adhesions were significantly lower in MAR-1 (11.22% ± 5.5%) compared to NaCl (58.57% ± 11.83%). Degradation of the glue was observed and MAR-1 showed almost no traces of glue in the abdominal cavity as compared to the Fibrin (10% ± 5% 14 d; 7% ± 3% 21 d). Survival showed no significant differences between the groups. CONCLUSION: Compared to Fibrin, MAR-1 showed similar hemostatic properties, no adverse effects, and is biocompatible. Further studies on adhesion strength and biodegradability of synthetic sealants are warranted.
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    19. 19
      Lee, C. The Mechanical Properties of PMMA Bone Cement. In The Well-Cemented Total Hip Arthroplasty: Theory and Practice; Springer: Berlin Heidelberg, 2005; 60– 66.
      There is no corresponding record for this reference.
    20. 20
      Torini, L.; Argillier, J. F.; Zydowicz, N. Interfacial Polycondensation Encapsulation in Miniemulsion. Macromolecules 2005, 38, 3225– 3236,  DOI: 10.1021/ma047808e
      20
      Interfacial polycondensation encapsulation in miniemulsion
      Torini, L.; Argillier, J. F.; Zydowicz, N.
      Macromolecules (2005), 38 (8), 3225-3236CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
      Oily core polyurethane nanocapsules with a mean diam. of 200 nm were formulated in miniemulsion by interfacial polycondensation. The encapsulation process in miniemulsion was optimized by the choice of the surfactant type (anionic, cationic, or nonionic) and concn.; hexadecane was the costabilizer. Size distribution was studied by dynamic laser light scattering, and ζ potential was also detd. The size distribution appeared relatively narrow. Scanning and TEM expts. attested for the submicrometer size, the spherical shape of the capsules, and a smooth external wall. The thermal properties of the polyurethane wall were detd. by DSC and TGA, with a fusion temp. around 40 °C, suggesting the presence of defaults in the macromol. backbone such as irregular bounds of urethane and urea functions. The chem. structure of the polymer wall was studied by 13C NMR and MALDI-TOF mass spectrometry. Both methods attested for the presence of urethane and urea units in the macromol. chain. MALDI-TOF expts. allowed the study of the microstructure of the polymer wall and proved the presence of urethane and urea homopolymer and urethane-urea copolymer. Although the detn. of the mol. wt. was not possible because of the high polydispersity of the sample, the mass range was comprised between 500 and 3000 Da, in accordance with the no.-av. mol. wt. detd. by size exclusion chromatog. (PS stds.).
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    21. 21
      Guo, J.; Pan, Q.; Huang, C.; Zhao, Y.; Ouyang, X.; Huo, Y.; Duan, S. The role of surfactant and costabilizer in controlling size of nanocapsules containing TEGDMA in miniemulsion. J. Wuhan Univ. Technol.-Mater. Sci. Ed. 2009, 24, 1004– 1006,  DOI: 10.1007/s11595-009-7004-2
      21
      The role of surfactant and costabilizer in controlling size of nanocapsules containing TEGDMA in miniemulsion
      Guo, Jinxin; Pan, Qiuhua; Huang, Cui; Zhao, Yanbing; Ouyang, Xiaobai; Huo, Yonghong; Duan, Sansan
      Journal of Wuhan University of Technology, Materials Science Edition (2009), 24 (6), 1004-1006CODEN: JWUTE8; ISSN:1000-2413. (Wuhan University of Technology)
      Nanocapsules with triethylene glycol dimethacrylate (TEGDMA) as core material and polyurethane as wall material used for self-healing bonding resin were prepd. by interfacial polycondensation in miniemulsion. The influence of surfactant and costabilizer concn. on nanocapsules size and stability of nanocapsules was investigated. The size and its polydispersity of the nanocapsules were measured by light-scattering particle size analyzer. When the concn. of SDS were increased from 2.5wt% to 10wt%, the size decreases from 340.5 nm to 258.3 nm, PDI decreased from 0.210 to 0.111. As the concn. of HD increased, the size and PDI were both decreased, When reaching 10wt%, the size was 258.0 nm, PDI was 0.130. SDS and HD play important effect in synthesis of Nanocapsules contg. TEGDMA. By changing the surfactant and costabilizer concn. it was possible to synthesize a wide variety of nanocapsules sizes. The performance and tech. parameters of nanocapsules had been researched preliminarily, which built the solid foundation for the application to the self-repairing bonding resin.
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    22. 22
      (a) Kaizer, M. R.; Almeida, J. R.; Goncalves, A. P.; Zhang, Y.; Cava, S. S.; Moraes, R. R. Silica Coating of Nonsilicate Nanoparticles for Resin-Based Composite Materials. J. Dent. Res. 2016, 95, 1394– 1400,  DOI: 10.1177/0022034516662022
      22a
      Silica coating of nonsilicate nanoparticles for resin-based composite materials
      Kaizer, M. R.; Almeida, J. R.; Goncalves, A. P. R.; Zhang, Y.; Cava, S. S.; Moraes, R. R.
      Journal of Dental Research (2016), 95 (12), 1394-1400CODEN: JDREAF; ISSN:0022-0345. (Sage Publications)
      This study was designed to develop and characterize a silica-coating method for cryst. nonsilicate ceramic nanoparticles (Al2O3, TiO2, and ZrO2). The hypothesis was that the coated nonsilicate nanoparticles would stably reinforce a polymeric matrix due to effective silanation. Silica coating was applied via a sol-gel method, with tetra-Et orthosilicate as a silica precursor, followed by heat treatment. The chem. and microstructural characteristics of the nanopowders were evaluated before and after silica coating through x-ray diffraction, BET (Brunauer-Emmett-Teller), energy-dispersive x-ray spectroscopy, field emission SEM, and transmission electron microscopy analyses. Coated and noncoated nanoparticles were silanated before prepn. of hybrid composites, which contained glass microparticles in addn. to the nanoparticles. The composites were mech. tested in 4-point bending mode after aging (10,000 thermal cycles). Results of all chem. and microstructural analyses confirmed the successful obtaining of silica-coated nanoparticles. Two distinct aspects were obsd. depending on the type of nanoparticle tested: 1) formation of a silica shell on the surface of the particles and 2) nanoparticle clusters embedded into a silica matrix. The aged hybrid composites formulated with the coated nanoparticles showed improved flexural strength (10% to 30% higher) and work of fracture (35% to 40% higher) as compared with composites formulated with noncoated nanoparticles. The tested hypothesis was confirmed: silanated silica-coated nonsilicate nanoparticles yielded stable reinforcement of dimethacrylate polymeric matrix due to effective silanation. The silica-coating method presented here is a versatile and promising novel strategy for the use of cryst. nonsilicate ceramics as a reinforcing phase of polymeric composite biomaterials.
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      (b) Li, L.; Zuo, Y.; Zou, Q.; Yang, B.; Lin, L.; Li, J.; Li, Y. Hierarchical Structure and Mechanical Improvement of an n-HA/GCO-PU Composite Scaffold for Bone Regeneration. ACS Appl. Mater. Interfaces 2015, 7, 22618– 22629,  DOI: 10.1021/acsami.5b07327
      22b
      Hierarchical Structure and Mechanical Improvement of an Nanohydroxyapatite/Glyceride of Castor Oil-Polyurethane Composite Scaffold for Bone Regeneration
      Li, Limei; Zuo, Yi; Zou, Qin; Yang, Boyuan; Lin, Lili; Li, Jidong; Li, Yubao
      ACS Applied Materials & Interfaces (2015), 7 (40), 22618-22629CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      To improve the mech. properties of bone tissue and achieve the desired bone tissue regeneration for orthopedic surgery, newly designed hydroxyapatite/polyurethane (HA/PU) porous scaffolds were developed via in situ polymn. The results showed that the mol. modification of PU soft segments by glyceride of castor oil (GCO) can increase the scaffold compressive strength by 48% and the elastic modulus by 96%. When nano-HA (n-HA) particles were incorporated into the GCO-PU matrix, the compressive strength and elastic modulus further increased by 49 and 74%, from 2.91 to 4.34 MPa and from 95 to 165.36 MPa, resp. The n-HA particles with fine dispersity not only improved the interface bonding with the GCO-PU matrix but also provided effective bioactivity for bonding with bone tissue. The hierarchical structure and mech. quality of the n-HA/GCO-PU composite scaffold were detd. to be appropriate for the growth of cells and the regeneration of bony tissues, demonstrating promising prospects for bone repair and regeneration.
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      (c) Mohr, R.; Kratz, K.; Weigel, T.; Lucka-Gabor, M.; Moneke, M.; Lendlein, A. Initiation of shape-memory effect by inductive heating of magnetic nanoparticles in thermoplastic polymers. Proc. Natl. Acad. Sci. U. S. A. 2006, 103, 3540– 3545,  DOI: 10.1073/pnas.0600079103
      22c
      Initiation of shape-memory effect by inductive heating of magnetic nanoparticles in thermoplastic polymers
      Mohr, R.; Kratz, K.; Weigel, T.; Lucka-Gabor, M.; Moneke, M.; Lendlein, A.
      Proceedings of the National Academy of Sciences of the United States of America (2006), 103 (10), 3540-3545CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
      In shape-memory polymers, changes in shape are mostly induced by heating, and exceeding a specific switching temp., Tswitch. If polymers cannot be warmed up by heat transfer using a hot liq. or gaseous medium, noncontact triggering will be required. The magnetically induced shape-memory effect of composites comprising magnetic nanoparticles and thermoplastic shape-memory polymers was studied. A polyetherurethane (TFX) and a biodegradable multiblock copolymer (PDC) with poly(p-dioxanone) as hard segment and poly(ε-caprolactone) as soft segment were studied as matrix component. Nanoparticles consisting of an iron(III) oxide core in a silica matrix were processed into both polymers. A homogeneous particle distribution in TFX could be shown. The composites have suitable elastic and thermal properties for the shape-memory functionalization. Temporary shapes of TFX composites were obtained by elongating at increased temp. and subsequent cooling under const. stress. Cold-drawing of PDC compds. at 25° resulted in temporary fixation of the mech. deformation by 50-60%. The shape-memory effect of both composite systems could be induced by inductive heating in an alternating magnetic field (f = 258 kHz; H = 30 kA·m-1). The max. temps. achievable by inductive heating in a specific magnetic field depend on sample geometry and nanoparticle content. Shape recovery rates of composites resulting from magnetic triggering are comparable to those obtained by increasing the environmental temp.
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    23. 23
      Wool, R. P.; O’Connor, K. M. A theory crack healing in polymers. J. Appl. Phys. 1981, 52, 5953– 5963,  DOI: 10.1063/1.328526
      23
      A theory of crack healing in polymers
      Wool, R. P.; O'Connor, K. M.
      Journal of Applied Physics (1981), 52 (10), 5953-63CODEN: JAPIAU; ISSN:0021-8979.
      A theory of crack healing in polymers is presented in terms of the stages of crack healing: surface rearrangement, surface approach, wetting, diffusion, and randomization. The recovery ratio R of mech. properties with time was detd. as a convolution product of an intrinsic healing function and a wetting distribution function for the crack interface or plane in the material. The reptation model of a chain in a tube was used to describe self-diffusion of interpenetrating random coil chains which formed a basis for the intrinsic healing function. Applications of the theory are described, including crack healing in amorphous polymers and melt processing of polymer resins by injection or compression molding. Relations are developed for fracture stress, strain, and energy as a function of time, temp., pressure, and mol. wt. Most of the theor. predictions were verified exptl. Chain fracture, creep, and stress relaxation are also discussed. The concepts for strength predictions are introduced.
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    24. 24
      Menikheim, S.; Leckron, J.; Bernstein, S.; Lavik, E. B. On-Demand and Long-Term Drug Delivery from Degradable Nanocapsules. ACS Appl. Bio Mater. 2020, 3, 7369– 7375,  DOI: 10.1021/acsabm.0c01130
      24
      On-Demand and Long-Term Drug Delivery from Degradable Nanocapsules
      Menikheim, Sydney; Leckron, Joshua; Bernstein, Steven; Lavik, Erin B.
      ACS Applied Bio Materials (2020), 3 (11), 7369-7375CODEN: AABMCB; ISSN:2576-6422. (American Chemical Society)
      We have developed polyurethane nanocapsules as a platform for long-term delivery of drugs over weeks as well as on-demand delivery of drugs via ultrasound. We synthesized nanocapsules encapsulating either a model drug, fluorescein, or a clin. relevant drug, acriflavine, a HIF-1alpha inhibitor. Release studies demonstrated delivery of fluorescein or acriflavine over several weeks. Application of either an ultrasonic probe or a clin. grade, ultrasound imaging system used for assessing the retina led to release of a fraction of drug that could be tailored by the energy applied to the nanocapsules, and multiple pulses of release could be triggered over time with at least 10 sep. release events triggered for each formulation. Being able to tailor the on-demand release over multiple cycles has the potential to fundamentally change how we can approach delivery of drugs for a variety of applications.
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    25. 25
      Diesendruck, C. E.; Sottos, N. R.; Moore, J. S.; White, S. R. Biomimetic Self-Healing. Angew. Chem., Int. Ed. 2015, 54, 10428– 10447,  DOI: 10.1002/anie.201500484
      25
      Biomimetic Self-Healing
      Diesendruck, Charles E.; Sottos, Nancy R.; Moore, Jeffrey S.; White, Scott R.
      Angewandte Chemie, International Edition (2015), 54 (36), 10428-10447CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Self-healing is a natural process common to all living organisms which provides increased longevity and the ability to adapt to changes in the environment. Inspired by this fitness-enhancing functionality, which was tuned by billions of years of evolution, scientists and engineers have been incorporating self-healing capabilities into synthetic materials. By mimicking mech. triggered chem. as well as the storage and delivery of liq. reagents, new materials have been developed with extended longevity that are capable of restoring mech. integrity and addnl. functions after being damaged. This Review describes the fundamental steps in this new field of science, which combines chem., physics, materials science, and mech. engineering.
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    26. 26
      Yehye, W. A.; Rahman, N. A.; Ariffin, A.; Abd Hamid, S. B.; Alhadi, A. A.; Kadir, F. A.; Yaeghoobi, M. Understanding the chemistry behind the antioxidant activities of butylated hydroxytoluene (BHT): A review. Eur. J. Med. Chem. 2015, 101, 295– 312,  DOI: 10.1016/j.ejmech.2015.06.026
      26
      Understanding the chemistry behind the antioxidant activities of butylated hydroxytoluene (BHT): A review
      Yehye, Wageeh A.; Abdul Rahman, Noorsaadah; Ariffin, Azhar; Bee Abd Hamid, Sharifah; Alhadi, Abeer A.; Kadir, Farkaad A.; Yaeghoobi, Marzieh
      European Journal of Medicinal Chemistry (2015), 101 (), 295-312CODEN: EJMCA5; ISSN:0223-5234. (Elsevier Masson SAS)
      A review. Hindered phenols find a wide variety of applications across many different industry sectors. Butylated hydroxytoluene (BHT) is a most commonly used antioxidant recognized as safe for use in foods contg. fats, pharmaceuticals, petroleum products, rubber and oil industries. In the past two decades, there has been growing interest in finding novel antioxidants to meet the requirements of these industries. To accelerate the antioxidant discovery process, researchers have designed and synthesized a series of BHT derivs. targeting to improve its antioxidant properties to be having a wide range of antioxidant activities markedly enhanced radical scavenging ability and other phys. properties. Accordingly, some structure-activity relationships and rational design strategies for antioxidants based on BHT structure have been suggested and applied in practice. We have identified 14 very sensitive parameters, which may play a major role on the antioxidant performance of BHT. In this review, we attempt to summarize the current knowledge on this topic, which is of significance in selecting and designing novel antioxidants using a well-known antioxidant BHT as a building-block mol. Our strategy involved investigation on understanding the chem. behind the antioxidant activities of BHT, whether through hydrogen or electron transfer mechanism to enable promising anti-oxidant candidates to be synthesized.
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    27. 27
      Keller, M. W.; Sottos, N. R. Mechanical Properties of Microcapsules Used in a Self-Healing Polymer. Exp. Mech. 2006, 46, 725– 733,  DOI: 10.1007/s11340-006-9659-3
      27
      Mechanical properties of microcapsules used in a self-healing polymer
      Keller, M. W.; Sottos, N. R.
      Experimental Mechanics (2006), 46 (6), 725-733CODEN: EXMCAZ; ISSN:0014-4851. (Springer)
      The elastic modulus and failure behavior of poly(urea-formaldehyde) shelled microcapsules were detd. through single-capsule compression tests. Capsules were tested both dry and immersed in a fluid isotonic with the encapsulant. The testing of capsules immersed in a fluid had little influence on mech. behavior in the elastic regime. Elastic modulus of the capsule shell wall was extd. by comparison with a shell theory model for the compression of a fluid filled microcapsule. Av. capsule shell wall modulus was 3.7 GPa, regardless of whether the capsule was tested immersed or dry. Microcapsule diam. was found to have a significant effect on failure strength, with smaller capsules sustaining higher loads before failure. Capsule size had no effect on the modulus value detd. from comparison with theory.
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    28. 28
      (a) Ouyang, X.; Huang, X.; Pan, Q.; Zuo, C.; Huang, C.; Yang, X.; Zhao, Y. Synthesis and characterization of triethylene glycol dimethacrylate nanocapsules used in a self-healing bonding resin. J. Dent. 2011, 39, 825– 833,  DOI: 10.1016/j.jdent.2011.09.001
      28a
      Synthesis and characterization of triethylene glycol dimethacrylate nanocapsules used in a self-healing bonding resin
      Ouyang, Xiaobai; Huang, Xueqing; Pan, Qiuhua; Zuo, Chenqi; Huang, Cui; Yang, Xiangliang; Zhao, Yanbing
      Journal of Dentistry (Oxford, United Kingdom) (2011), 39 (12), 825-833CODEN: JDENAB; ISSN:0300-5712. (Elsevier Ltd.)
      To date, the prodn. of highly durable dentin bonding is still a challenge. Self-healing bonding resins may provide a new direction for the improvement of the bonding durability. The objective of the current study was to synthesize polyurethane nanocapsules encapsulated with the core material triethylene glycol dimethacrylate (TEGDMA) for use as a major component in a self-healing bonding resin. TEGDMA nanocapsules were synthesized via interfacial polycondensation in a miniemulsion, and the TEGDMA nanocapsules were then characterized via Fourier-transform IR (FTIR) spectrometer, field emission SEM (FESEM), and high-performance liq. chromatog. (HPLC) to investigate the morphol., the av. TEGDMA loading (DL%), and encapsulation efficiency (EE%). The mech. property of dental adhesive with different concns. (0, 3, 6, 9, and 12 wt%) of the TEGDMA nanocapsules were also measured, and the cytotoxicity was investigated using an MTT assay. FTIR confirmed that the TEGDMA nanocapsules were successfully synthesized. These nanocapsules showed a high drug load. The bond strength of the dental adhesive incorporated with 9 wt% TEGDMA nanocapsules was significantly higher compared with those of the other groups (P < 0.001). Moreover, the biocompatibility of the dental adhesive was not affected by the incorporation of the TEGDMA nanocapsules. The current study demonstrated the successful synthesis of TEGDMA nanocapsules, and the overall properties of the dental adhesive were not compromised.
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      (b) El-Ansary, A.; Al-Daihan, S.; Bacha, A. B.; Kotb, M. Toxicity of novel nanosized formulations used in medicine. Methods Mol. Biol. 2013, 1028, 47– 74,  DOI: 10.1007/978-1-62703-475-3_4
      28b
      Toxicity of novel nanosized formulations used in medicine
      El-Ansary, Afaf; Al-Daihan, Sooad; Ben Bacha, Abir; Kotb, Malak
      Methods in Molecular Biology (New York, NY, United States) (2013), 1028 (Oxidative Stress and Nanotechnology), 47-74CODEN: MMBIED; ISSN:1064-3745. (Springer)
      A review. Nanotechnol. involves the creation and manipulation of materials at nanoscale levels (1-100 nm) to create products that exhibit novel properties. While this motivation has driven nanoscience and technol. in physics and engineering, it is not the main reason that nanoparticles are useful for systemic applications in the human body. The application of nanotechnol. to medicine, known as nanomedicine, concerns the use of precisely engineered materials at this length scale to develop novel therapeutic and diagnostic modalities. A no. of nanotherapeutic formulations are already approved for medical use and more are in the approval pipeline currently. This chapter is intended to provide an overview of the toxicity of these therapeutic nanoparticles and to summarize the current state of the field. We begin with background on the sources of exposure to nanoparticles, followed by reviewing different forms of nanosized therapeutic tools as quantum dots, nanoshells, nanocapsules, echogenic bubble, and "nanoshuttles.". Moreover, cytotoxic effects of nanoparticles on cell membrane, mitochondrial function, prooxidant/antioxidant status, enzyme leakage, DNA, and other biochem. endpoints were elucidated. We highlight the need for caution during the use and disposal of such manufd. nanomaterials to prevent unintended environmental impacts. Moreover, different strategies which could be used to minimize or eliminate nanotoxicity were also discussed in detail. Understanding of how to tune size and surface properties to provide safety will permit the creation of new, more effective nanomedicines for systemic use.
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      (c) Picheth, G.; Houvenagel, S.; Dejean, C.; Couture, O.; Alves de Freitas, R.; Moine, L.; Tsapis, N. Echogenicity enhancement by end-fluorinated polylactide perfluorohexane nanocapsules: Towards ultrasound-activable nanosystems. Acta Biomater. 2017, 64, 313– 322,  DOI: 10.1016/j.actbio.2017.10.002
      28c
      Echogenicity enhancement by end-fluorinated polylactide perfluorohexane nanocapsules: Towards ultrasound-activable nanosystems
      Picheth, Guilherme; Houvenagel, Sophie; Dejean, Camille; Couture, Olivier; Alves de Freitas, Rilton; Moine, Laurence; Tsapis, Nicolas
      Acta Biomaterialia (2017), 64 (), 313-322CODEN: ABCICB; ISSN:1742-7061. (Elsevier Ltd.)
      Polylactide (PLA) polymers contg. five distinct lengths of fluorinated (from C3F7 to C13F27) and non-fluorinated (C6H13) end-groups were successfully synthesized by ring-opening polymn. of D,L-lactide. Fluorination was expected to increase the encapsulation efficiency of perfluorohexane (PFH). 150 nm nanocapsules were obtained and 19F NMR revealed that nanocapsules formulated with fluorinated polymers increased by 2-fold the encapsulation efficiency of PFH compared with non-fluorinated derivs., without any effect of fluorine chain length. Fluorination of the polymers did not induce any specific in vitro cytotoxicity of nanocapsules towards HUVEC and J774.A1 cell lines. The echogenicity of fluorinated-shelled nanocapsules was increased by 3-fold to 40-fold compared to non-fluorinated nanocapsules or nanoparticles devoid of a perfluorohexane core for both conventional and contrast-specific ultrasound imaging modalities. In particular, an enhanced echogenicity and contrast-specific response was obsd. as the fluorinated chain-length increased, probably due to an increase of d. and promotion of bubble nucleation. When submitted to focused ultrasound, both intact and exploded nanocapsules could be obsd., also with end-group dependency, indicating that PFH was partly vaporized. These results pave the way to the design of theranostic perfluorohexane nanocapsules co-encapsulating a drug for precision delivery using focused ultrasound. We believe that Acta Biomaterialia is an appropriate journal for our article since we present new and original exptl. research in the field of nanomaterials for biomedical applications. In particular, we have synthesized novel fluorinated polyesters and formulated them into nanocapsules of perfluorohexane as ultrasound contrast agents. This nanosystem has been thoroughly characterized by several techniques and we show that fluorination of the biodegradable polymer favors the encapsulation of perfluorohexane without producing further redn. of cell viability. Contrary to nanocapsules of perfluoroctyl bromide formulated with the fluorinated polymers [32], the presence of the fluorinated moieties leads to an increase of echogenicity that is dependent of the length of the fluorinated moiety. Morevover, the ability of nanocapsules to explode when submitted to focused ultrasound also depends on the length of the fluorinated chain. These results pave the way to theranostic perfluorohexane nanocapsules co-encapsulating a drug for precision delivery using focused ultrasound.
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      (d) Montigaud, Y.; Ucakar, B.; Krishnamachary, B.; Bhujwalla, Z. M.; Feron, O.; Préat, V.; Danhier, F.; Gallez, B.; Danhier, P. Optimized acriflavine-loaded lipid nanocapsules as a safe and effective delivery system to treat breast cancer. Int. J. Pharm. 2018, 551, 322– 328,  DOI: 10.1016/j.ijpharm.2018.09.034
      28d
      Optimized acriflavine-loaded lipid nanocapsules as a safe and effective delivery system to treat breast cancer
      Montigaud, Yoann; Ucakar, Bernard; Krishnamachary, Balaji; Bhujwalla, Zaver M.; Feron, Olivier; Preat, Veronique; Danhier, Fabienne; Gallez, Bernard; Danhier, Pierre
      International Journal of Pharmaceutics (Amsterdam, Netherlands) (2018), 551 (1-2), 322-328CODEN: IJPHDE; ISSN:0378-5173. (Elsevier B.V.)
      Acriflavine (ACF) hydrochloride is currently repurposed as multimodal drug, inhibiting hypoxia-inducible factors (HIF) pathways and exerting cytotoxic properties. The aim of this study was to encapsulate ACF in reverse micelles and to incorporate this suspension in lipid nanocapsules (LNC). Designs of expts. were used to work under quality by design conditions. LNC were formulated using a phase-inversion temp. method, leading to an encapsulation efficiency around 80%. In vitro, the encapsulated drug presented similar cytotoxic activity and decrease in HIF activity in 4T1 cells compared to the free drug. In vivo, ACF-loaded nanoparticles (ACF dose of 5 mg/kg) demonstrated a higher antitumor efficacy compared to free ACF on an orthotopic model of murine breast cancer (4T1 cells). Moreover, the use of LNC allowed to drastically decrease the no. of administrations compared to the free drug (2 vs. 12 injections), suppressing the ACF-induced toxicity.
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  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.2c02080.

    • Supplemental information is included in order to better describe the monomer and initiator capsule characteristics in addition to increase the comprehension of the self-healing reaction. Additionally, the supplemental information contains more details from the mechanical tests performed (PDF)


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