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

• E-SSG's excellent impact resistance, shape recoverability and damping could find many applications ranging from protective, medical and sports devices to robotics and electronics packaging. • Owing to the 3D printing process, the mechanical properties of E-SSG can be locally tailored, opening new opportunities for bespoke devices that mimic their wearer. • The synergistic energy absorption and dissipation at the interface may lead to new and better composite performance, particularly coupled to complex 3D printed geometries. • The hybrid 3D printing and casting approach may also aid in increasing adoption of 3D printed parts by partially mitigating its slow rate of production. 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.