Modeling and Characterization of Polydimethylsiloxane (PDMS) Pillar Arrays for Biological Applications

摘要

The mechanical interaction force between cells and their neighboring extracellular matrix is believed to be very important in various physiological processes and which can be measured by soft material probes. Polydimethylsiloxane (PDMS) is an important polymeric material widely used in bio-MEMS devices such as micropillar arrays for cellular mechanical force measurements. The accuracy of such a measurement relies on choosing an appropriate material constitutive model for converting the measured structural deformations into corresponding reaction forces. However, although PDMS is a well-known viscoelastic material, many researchers in the past have treated it as a linear elastic material and employed the simple cantilever beam equation to calculate the force from observed deflection, which could result in errors of cellular traction force interpretation. In this paper, the mechanical properties of PDMS were characterized by using uniaxial compression, dynamic mechanical analysis, and nanoindentation tests in both macro- and micro- scales, as well as finite element analysis. A generalized Maxwell model with the use of two exponential terms was used to emulate the mechanical behavior of PDMS at room temperature and the subsequent nanoindentation characterizations. After we found the viscoelastic constitutive law of PDMS, we used it to develop a more accurate model for converting deflection data to cellular traction forces. The results indicate that the linear cantilever beam model could significantly overestimate the cellular forces. Furthermore, in situ cellular traction force evolutions of cardiac myocytes were demonstrated by using this new conversion model. The results presented by this paper are believed to be useful for biologists who are interpreting similar physiological processes.