Skin-Mimicking Soft Strain Sensor with Elastic Resilience, Crack Tolerance, and Amphibious Self-Adhesion

The intrinsic elastic resilience, fatigue resistance, and self-adhesion of human skin are highly desired merits. However, they are challenging to combine into a single mechanoreceptive electronic skin for healthcare monitoring and humanoid soft robots. We introduce an elastically resilient, crack-tolerant, amphibiously adhesive, and strain-sensitive electronic skin (ERCAS-skin) featuring a hierarchical and gradient design. ERCAS-skin has a skin-like binary structure of a carbon nanotube-coated thermoplastic polyurethane nanofibrous scaffold embedded in a gradient cross-linking polydimethylsiloxane (PDMS) matrix. The binary structure endows ERCAS-skin with mechanical compliance (Young's modulus of 2.4 MPa) and crack tolerance (fatigue threshold of 1285 J m^-2) through a matrix-to-scaffold stress transfer. The gradient cross-linking PDMS ensures not only high elastic resilience (recovery of 95%) but also strong wet adhesion (0.76 N cm^-1) through a synergistic hydrophobic chain mobility effect. The crack generation mechanism of the embedded carbon nanotube polyurethane enables high sensitivity and a wide strain-sensing range. Owing to its excellent strain-sensing capability, ERCAS-skin was utilized as a self-adhesive strain sensor for hand gesture recognition both in the air and under water and as a fatigue-free motion sensor for robotic fish monitoring.