Spatially programming stretchability in an elastomer composite with UV light

Spatial modulation of stretchability is advantageous for applications including on-skin electronics, soft robotics, and deployable shape-morphing structures. In this work, we combine silicone elastomer and UV-curable thermoset resin to form an interpenetrating polymer network with orthogonal cross-linking reactions. The composite can be selectively UV-treated to create regions of high and low stretchability within a structure or substrate. By modifying the material components, composition ratios, and UV-exposure time, a range of stiffnesses and extensibilities can be embodied in the composite material. Features with varying stretchability can be spatially patterned with length scales from micro- to macroscale using laser micromachining, digital light projection, and photolithography approaches. We demonstrate how this material can be structured not only with a priori design-and-fabricate approaches to create immutable structures, but also with on-the-fly modification of material mechanics through the combined application of strain and UV-treatment. This combination of inputs to the composite substrate can be leveraged to create 3D structures that could not be achieved with a single-step patterning process and to alter the trajectory and form of inflatable, deployable structures.