Elastic shear-stiffening composites with locally tunable mechanics for protection and damping

Shear-stiffening gels are flexible materials whose modulus is significantly increased upon rapid impact. They have applications in protective and other devices but are generally limited by difficult processability and poor shape retention. Here we demonstrate a simple and scalable process for making elastic shear-stiffening composites with locally controllable and complex geometries. We construct elastic shear-stiffening composites combining mechanical integrity with shear-stiffening behaviour and elasticity. Shear-stiffening gels were 3D-printed as thin fibres with interstitial spaces filled with polydimethylsiloxane elastomer to hold the gels in place. The composite exhibits strong impact-resistance and shape recovery, which may be due to synergistic energy absorption and dissipation at the composite interface, as well as to the elastomer architecture. Composite mechanics can also be locally modulated by tuning the infill percentages to selectively vary part stiffness and therefore aid motion and wearer comfort. Similarly, a composite hinge exhibits excellent damping, shown in a robotic demonstration.