Highly strong, tough and conductive hydrogels via the synergy of biomineralization, salting-out effect and nano-reinforcement with enhanced human motion sensing properties

Abstract

Conductive hydrogels have shown considerable potential for various applications in advanced flexible electronic systems and wearable devices. However, obtaining hydrogels that simultaneously possess robust mechanical characteristics and high conductivity remains challenging because of their structural weaknesses and functional constraints. To address this problem, we purposed a facile preparation method for PVA/CaCl₂/Graphite/Na₃Cit/Na₂CO₃ composite hydrogel leveraging the synergistic effect of biomineralization, salting-out effect and nano-reinforcement strategy. The fabrication process involved first preparation of a homogeneous mixture solution of PVA, glycerol, graphite, and CaCl₂ in deionized water. Then Na₂CO₃ solution was slowly added under stirring. The obtained composite solution was cast into molds and subjected to freeze-thaw cycles. Final treatment through immersion in Na₃Cit solution yielded the optimized PCGSN hydrogel. The fabricated PCGSN hydrogel demonstrated outstanding mechanical properties including tensile strength of 4.1 MPa, Young's modulus of 1.2 MPa, and toughness reaching 13.30 MJ m⁻³, respectively. Moreover, the integration of graphite and salt ions enhanced the hydrogel's conductivity as high as 1.56 S/m. Through the combined influence of salting-out effect and glycerol incorporation, the hydrogen bond density within the hydrogel was significantly improved, leading to remarkable self-healing performance (with a healing efficiency exceeding 85 %). When implemented as strain sensors, PCGSN-based devices showed outstanding responsiveness (GF = 1.27) across a broad detection range (1–300 % strain), enabling precise tracking of both gross motor activities (joint movements) and fine physiological signals (facial expressions). This work provides a new insight into the preparation of strong and tough hydrogel based on biomineralization, salting-out effect and nano-reinforcement strategy.