Plant Inspired Soft Material Composite with Liquid Encapsulations

Plants are unique mechanical structures that combine high water content with structural elements. Unlike common soft material and liquid composites (ex: hydrogel), plants compartmentalize their water using semi-permeable membranes. We synthesize plant tissue analogs, idealized as closely packed water droplets surrounded by thin walls of PDMS, to understand their mechanical response. The analogs are created by high internal phase emulsion templating. We choose PDMS because it is highly stretchable and semipermeable yet does not swell in water. It also has a tunable modulus that allows us to capture the varied range of stiffness in flora. However, due to the high viscosity of PDMS prepolymer, adding large quantities of water to the emulsion demands very high shear force. Using microfluidics is also difficult because high pressure – required to make PDMS flow through the channels – easily ruptures device assembly. To overcome these challenges, we combine shear-mixing with centrifugation. The influence of viscosity ratio, amount of stabilizer, and fabrication specifics on droplet generation and structure are investigated. We find that with careful manipulation of the above governing parameters, the micromorphology of the composite can be designed to within plant-cell relevant ranges.