Topological Self-Locking of Hyperbranched Poly(ionic liquid)s for Impact-Stiffening Ionic Skins

Abstract Impact-stiffening ionic skins are highly promising for bioelectronics due to their unique ability to maintain ambient softness and ionic conductivity while instantly hardening upon impact. However, the intrinsically low entropy penalty of ionic bonds typically restricts their strain-rate sensitivity, thereby dampening the overall impact-stiffening performance. To overcome this bottleneck, we report a topological self-locking strategy to exponentially boost the impact-stiffening response of ionic skins. By engineering a hyperbranched poly(ionic liquid) network, we achieved a dramatic, impact-induced transition from a viscous chain-sliding state (shear storage modulus, G′ ∼ 12 kPa at 0.1 Hz) to a rigid glassy self-locked state (G′ ∼ 70.3 MPa at 100 Hz). This topological transition yields a significant 5858-fold increase in stiffness, outperforming most state-of-the-art materials. Furthermore, the developed ionic skin demonstrates great potential for simultaneous impact resistance and high-fidelity sensing. This topological self-locking approach offers a new protective paradigm for soft materials, bypassing the need for conventional particulate jamming or specific dynamic bonds.