A Tough and Self-Powered Hydrogel for Artificial Skin

TLDR

Hydrogels mimic skin’s water‑rich, soft mechanics, yet existing piezoresistive variants suffer from weak mechanical strength and dependence on external power. The authors develop a tough, self‑powered hydrogel that fuses a polyacrylonitrile matrix with ferroelectric poly(vinylidene fluoride) to overcome these shortcomings. The composite achieves 91.3 % β‑phase PVDF, a d33 of 30 pC N⁻¹, skin‑like modulus (1.33–4.24 MPa), 90–175 % stretchability, 1.23 MJ m⁻² toughness, and generates ≈30 mV, ≈2.8 µA with ≈31 ms response, enabling precise detection of gestures, pulse, and speech while providing a low‑cost, fast‑responding artificial skin.

Abstract

Hydrogels, because of their water-rich nature and soft mechanical characteristics that resemble those of skin tissues, are promising materials for artificial skin. Existing piezoresistive hydrogels combine unique tissue-like and sensory properties, but these materials are often plagued by problems such as poor mechanical properties and the requirement of an external power supply or batteries. Here, a tough and self-powered hydrogel based on a tough polyacrylonitrile hydrogel incorporating ferroelectric poly(vinylidene fluoride) (PAN-PVDF) is reported. The dipolar interactions between the PVDF and PAN chains cause an increase in the best electroactive β-phase PVDF percentage in the composites from 0 to 91.3%; thus, a maximum piezoelectric coefficient d33, 30 pC N–1, was achieved for the hydrogels. Skin-like Young's modulus values (1.33–4.24 MPa), stretchability (90–175%), and high toughness (1.23 MJ/m2) were achieved simultaneously for the hydrogels. This tough gel is capable of generating an electrical signal output (≈30 mV and ≈2.8 μA) with a rapid response (≈31 ms) due to the stress-induced poling effect. Moreover, the gel can also precisely detect physiological signals (e.g., gesture, pulse, and words). This study provides a simple and efficient method for artificial skin with high toughness, self-power generation capability, fast response, low cost, and tissue-like properties.