Highly Conductive, Stretchable, Adhesive, and Self-Healing Polymer Hydrogels for Strain and Pressure Sensor

Retractable, self-healing, and conductive hydrogels are widely used as adjustable and wearable sensing materials. Herein, using polyfunctional trypan blue (TB) as a crosslinking agent for both poly(acrylic acid) (PAA) and polypyrrole (PPy), a retractable and self-healing PAA-TB-PPy hydrogel is prepared. The introduction of TB not only improves the water retention capacity of the hydrogel but also helps form a highly interconnected conductive path. It is found that PAA-TB-PPy hydrogel shows a high electrical conductivity (15 S m⁻¹) which is almost equivalent to the pure PPy hydrogel. Due to the high stability of the semi-interpenetrating network structure, the elongation at break of PAA-TB-PPy hydrogel is more than 750%, along with high mechanical strength and strong adhesion to a variety of solid surfaces. In addition, the hydrogel exhibits high strain and pressure sensitivity with prominent linearity. Importantly, the as-prepared hydrogel sensor can reliably detect both repetitive large strain and subtle vibration, which makes it a great candidate as wearable electronics for human motion monitoring.