PDMS polymerized high internal phase emulsions (polyHIPEs) with closed-cell, aqueous-filled microcavities

Abstract

Emulsion templates can produce a wide range of unique microstructures via solidification of the continuous phase. Some of these structures result in unique, fluid-filled composites reminiscent of biological tissue when the templating droplets develop into closed-cell structures. However, the state-of-the-art falls short in replicating the mechanical and functional response of biological structures due to stiff, fragile, and bio-incompatible materials while lacking systematic processing parameters. This article describes the synthesis of high internal phase, closed-cell, polydimethylsiloxane (PDMS) elastomeric foams which simultaneously achieve biocompatibility, mechanical robustness, flexibility, and selective permeability. Water-in-oil high internal phase emulsions (HIPEs) stabilized by silica nano-particles (SNPs) provide the microstructural template, resulting in a >74% by volume aqueous phase (up to 82%). To overcome the prohibitive barrier to HIPE formation when using a mechanically-superior, but highly viscous commercial PDMS kit, we produce HIPE templates via centrifugation of low internal phase emulsions (LIPEs, <30% by volume dispersed phase). This oil phase crosslinks into an aqueous-filled (water + glycerol + NaCl) elastomeric composite. The composite's microstructural dependence on viscosity ratio, mixing speed, emulsifier concentration, and centrifugal force are systematically characterized. The resulting microstructured, fluid-filled elastomer composites exhibit mechanically robust and highly flexible behavior due to the excellent properties of the PDMS continuous phase.