Self-powered artificial skin made of engineered silk protein hydrogel

Engineered silk protein hydrogel that resembles skin tissue is a promising material for artificial electronic skin; it can be interfaced with real biological tissues seamlessly and used as an artificial tissue in soft robotics. Herein, we report a soft, biocompatible, and skin-adhesive silk hydrogel incorporating ZnO nanorods (ZnONRs) for a tribo- and piezo-electric energy-generating skin (EG-skin) that can harvest biomechanical energy and sense biomechanical motions. Incorporation of ZnONRs mediates an eight-fold enhancement of piezoelectricity compared to pristine silk hydrogel. An additional two-fold increase in the electrical response is possible when it is encapsulated in silk protein layers because of the hybrid effect of tribo- and piezo-electricity. The high power generated (~1 mW/cm2) is sufficient to activate low-power electrical devices, such as LEDs, oximeters, and stopwatches. Additionally, the EG-skin can be used as a tactile identifier for finger movements with quantized real-time electrical signals. The softness and skin-adhesive properties provide conformal interfaces with human skin and biological tissues, and we can harvest energies of approximately 6.2 and 0.9 μW/cm2, respectively, from their mechanical stimulation. The silk-protein-based artificial EG-skin can be effectively utilized in human–machine interfaces, tactile sensors, soft robotics, and biomedical implants.