A Skin-Inspired Substrate with Spaghetti-Like Multi-Nanofiber Network of Stiff and Elastic Components for Stretchable Electronics

Mimicking the skin's non-linear self-limiting mechanical characteristics is of great interest. Skin is soft at low strain but becomes stiff at high strain and thereby can protect human tissues and organs from high mechanical loads. Herein, the design of a skin-inspired substrate is reported based on a spaghetti-like multi-nanofiber network (SMNN) of elastic polyurethane (PU) nanofibers (NFs) sandwiched between stiff poly(vinyldenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) NFs layers embedded in polydimethylsiloxane elastomer. The elastic moduli of the stretchable skin-inspired substrate can be tuned in a range that matches well with the mechanical properties of skins by adjusting the loading ratios of the two NFs. Confocal imaging under stretching indicates that PU NFs help maintain the stretchability while adding stiff P(VDF-TrFE) NFs to control the self-limiting characteristics. Interestingly, the Au layer on the substrate indicates a negligible change in the resistance under cyclic (up to 7000 cycles at 35% strain) and dynamic stretching (up to 35% strain), which indicates the effective absorption of stress by the SMNN. A stretchable chemoresistive gas sensor on the skin-inspired substrate also demonstrates a reasonable stability in NO₂ sensing response under strain up to 30%. The skin-inspired substrate with SMNN provides a step toward ultrathin stretchable electronics.