Oxidation stiffening of PDMS microposts

This paper presents guidance for analyzing the stiffness changes of micropost arrays after oxidation. Numerous mechanobiology studies exploit micropost arrays to quantify cell-generated micropost displacements and traction forces. Cell adhesion requires surface functionalization typically facilitated by an oxidation step, which can form a glassy skin. We estimate the material properties of this skin, analytically calculate the stiffness of oxidized microposts and compare it with direct measurements. We find correction factors increase exponentially with decreasing micropost diameter. Ignoring this oxidation stiffening of microposts results in more than 200% underestimation in micropost stiffness as well as the cellular traction forces extracted from micropost deflections.