Facile preparation and high performance of wearable strain sensors based on ionically cross-linked composite hydrogels

Flexible sensors that can respond to multiple mechanical excitation modes and have high sensitivity are of great significance in the fields of electronic skin and health monitoring. Simulating multiple signal responses to skin such as strain and temperature remains an important challenge. Therefore, new multifunctional ion-crosslinked hydrogels with toughness and conductivity were designed and prepared in this work. A chemical gel with high mechanical strength was prepared by cross-linking acrylamide with N,N′-methylene-bisacrylamide and ammonium persulfate. In addition, in order to enhance the conductive properties of the hydrogel, Ca2+, Mg2+ and Al3+ ions were added to the hydrogel during cross-linking. The double-layer network makes this ionic hydrogel show excellent mechanical properties. Moreover, the composite hydrogel containing Ca2+ can reach a maximum stretch of 1100% and exhibits ultra-high sensitivity (S p = 10.690 MPa−1). The obtained hydrogels can successfully prepare wearable strain sensors, as well as track and monitor human motion. The present prepared multifunctional hydrogels are expected to be further expanded to intelligent health sensor materials.