Elastic and Self-Healing Copolymer Coatings with Antimicrobial Function

The revolutionary self-healing function for long-term and safe service processes has inspired researchers to implement them in various fields, including in the application of antimicrobial protective coatings. Despite the great advances that have been made in the field of fabricating self-healing and antimicrobial polymers, their poor transparency and the trade-off between the mechanical and self-healing properties limit the utility of the materials as transparent antimicrobial protective coatings for wearable optical and display devices. Considering the compatibility in the blending process, our group proposed a self-healing, self-cross-linkable poly{(n-butyl acrylate)-co-[N-(hydroxymethyl)acrylamide]} copolymer (AP)-based protective coating combined with two types of commercial cationic antimicrobial agents (i.e., dimethyl octadecyl (3-trimethoxysilylpropyl) ammonium chloride (DTSACL) and chlorhexidine gluconate (CHG)), leading to the fabrication of a multifunctional modified compound film of (AP/b%CHG)-grafted-a%DTSACL. The first highlight of this research is that the reactivity of the hydroxyl group in the N-(hydroxymethyl)acrylamide of the copolymer side chains under thermal conditions facilitates the “grafting to” process with the trimethoxysilane groups of DTSACL to form AP-grafted-DTSACL, yielding favorable thermal stability, improvement in hydrophobicity, and enhancement of mechanical strength. Second, we highlight that the addition of CHG can generate covalent and noncovalent interactions in a complex manner between the two biguanide groups of CHG with the AP and DTSACL via a thermal-triggered cross-linking reaction. The noncovalent interactions synergistically serve as diverse dynamic hydrogen bonds, leading to complete healing upon scratches and even showing over 80% self-healing efficiency on full-cut, while covalent bonding can effectively improve elasticity and mechanical strength. The soft nature of CHG also takes part in improving the self-healing of the copolymer. Moreover, it was discovered that the addition of CHG can enhance antimicrobial effectiveness, as demonstrated by the long-term superior antibacterial activity (100%) against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria and the antifouling function on a glass substrate and/or a silica wafer coated by the modified polymer.


S1. 1 H NMR analyses of the modified polymer
proposed: [1] represents the dehydration of the hydroxyl group on the NMA segment formed bis(methylene ether) by the loss of OH -and H + ; [2] represents the formation of a methylene bridge by the loss of formaldehyde between NMA side chains; and [3] represents the covalent linking of C-N= groups from the CHG structure with the NMA side chains.Furthermore, various types of non-covalent hydrogen interaction [1'] between NMA side chains and [2'-5'] between the NMA side chain and the two biguanide groups of CHG were also presented.(b) Enlargement from Figure 1d of normalized ATR-FTIR spectrum focusing on the range wavenumber of 1100 -1850 cm -1 .

Supporting Discussion:
Figure S4a shows the potential for the formation of a large number of covalent and noncovalent hydrogen bond networks capable of developing complex structures in the crosslinked modified polymer.FTIR spectroscopy was performed to demonstrate that the resultant thermally induced crosslinking reactions formed covalent and non-covalent interactions between the NMA side chains and between the NMA side chains and the CHG compound.As depicted in Figure S4b, the strong peaks at 1667 cm -1 and 1532 cm -1 are assigned to the amide I and amide II bands, respectively, which correspond to the amide groups of both the NMA side chain and the biguanide groups of CHG.Integral area reduction on Amide-I implies the =NH breakage of the biguanide group and the enhancement integral area at peak 1256 cm -1 confirming the covalent bond formation of the C-N-group. 1Meanwhile, the expansion of the integral area belonging to the C-O-C peak is well defined as the successful covalent bonding formation focusing on the AP system. 2 It was associated with the damage of hydroxy groups with the loss of OH -and H + accompanied by the formation of bis(methylene ether) between the NMA segments.

Figure S4 .
Figure S4.(a) Schematic illustration of the possible synergistic effect in the cross-linking reaction on the blended 1% CHG with AP.Three types of covalent bonding formations were

Figure S14 .
Figure S14.Appearance changes from the first to the 21 days of bread stored under cling wrap conditions at room temperature.There is no special treatment of bread before use.(AP/1%CHG)-grafted-3%DTSACL-coated silica wafer was embedded in the upper left corner of the bread.

Figure S15 .
Figure S15.Visual appearance of the white bread stored (a) with and (b) without antimicrobial treatment from day 1 to day 14.

Table Comparison Table S1 .
Summary of practical applications antimicrobial substances as coatings.

Table S2 .
Evaluation of the biocompatibility of each material used in this study based on other reported studies.

Table S3 .
Surface elemental areas, compositions, and functionality ratios of AP and AP/1%CHG obtained from XPS analysis.The sensitivity factor for C, N, O, and Cl elements were 0.31, 0.50, 0.73, and 0.95, respectively.

Table S4 .
List of prices, brands and quantities of chemicals required to synthesis PBA0.8-co-PNMA0.2embedded with CHG and DTSACL antimicrobial agents.