Polydopamine/polystyrene nanocomposite double-layer strain sensor hydrogel with mechanical, self-healing, adhesive and conductive properties.

Inspired by the adhesion mechanism of natural mussels, polydopamine (PDA) has been widely studied and applied in hydrogels due to its good adhesion to various materials. In this work, a double-layer hydrogel constituted of an adhesive layer and a tough layer was successfully prepared via in-situ polymerization. Adding polystyrene particles into the tough layer could improve the mechanical properties, and the adhesion of various substrates could be achieved with PDA nanoparticles in the adhesive layer. Furthermore, lithium chloride was introduced into the tough layer to endow the bilayer hydrogels with electrical conductivity. Due to the hydrophobic association in the tough layer and hydrogen bond in the adhesive layer, the double-layer hydrogel exhibits self-healing properties. In addition, the NIR light response property of PDA was beneficial to self-healing properties. As a result, it has proved that the prepared bilayer hydrogel has excellent conductivity, toughness (0.18 MPa), adhesion and self-healing properties, which is an ideal flexible wearable strain sensor with high sensitivity and good repeatability, suitable for human motion signal detection.