Web Release Date: April 30,
Stability of Microfabricated High Aspect Ratio Structures in Poly(dimethylsiloxane)
and
Unitat de Biofísica i Bioenginyeria, Facultat de Medicina, Universitat de Barcelona-IDIBAPS, Casanova 143, 08036 Barcelona, Spain, Laboratori de Nanobioenginyeria (CREBEC), and Plataforma de Nanotecnologia, Parc Científic de Barcelona, 08028 Barcelona, Spain
Received December 14, 2004
In Final Form: April 4, 2005
Abstract:
The stability of structures microfabricated in soft elastomeric polymers is an important concern in most
applications that use these structures. Although relevant for several applications, the collapse to the
ground of high aspect ratio structures (ground collapse) is still poorly understood. The stability of soft
microfabricated high aspect ratio structures versus ground collapse was experimentally assessed, and a
new model of ground collapse involving adhesion was developed. Sets of posts with diameters from 0.36
to 2.29 
m were fabricated in poly(dimethylsiloxane) and tested in air or immersed in water and ethanol
to change the work of adhesion. The critical aspect ratio (the highest length-to-width ratio for which a post
is not at risk of collapsing) was determined as a function of the diameter. The critical aspect ratio in air
ranged from 2 to 4 and increased with the diameter. Work of adhesion was found to be determinant for
and inversely correlated to stability. These results highlight the role played by adhesion and offer the
possibility of improving stability by reducing the work of adhesion. The ground collapse model developed
accounted for the main features of structure stability. The results indicate that ground collapse can be
a limiting factor in the design of soft polymer structures.
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