Highly conductive and tough polyacrylamide/sodium alginate hydrogel with uniformly distributed polypyrrole nanospheres for wearable strain sensors.

Conductive hydrogels have attracted widespread attention because of their integrated characteristics of being stretchable, deformable, adhesive, self-healable, and conductive. Herein, we report a highly conductive and tough double-network hydrogel based on a double cross-linked polyacrylamide (PAAM) and sodium alginate (SA) network with conducting polypyrrole nanospheres (PPy NSs) uniformly distributed in the network (PAAM-SA-PPy NSs). SA was employed as a soft template for synthesis of PPy NSs and distribution of PPy NSs uniformly in the hydrogel matrix to construct SA-PPy conductive network. The PAAM-SA-PPy NS hydrogel exhibited both high electrical conductivity (6.44 S/m) and excellent mechanical properties (tensile strength of 560 kPa at 870 %), as along as high toughness, high biocompatibility, good self-healing and adhesion properties. The assembled strain sensors showed high sensitivity and a wide sensing range (a gauge factor of 1.89 for 0-400 % strain and 4.53 for 400-800 % strain, respectively), as well as fast responsiveness and reliable stability. When used as a wearable strain sensor, it was able to monitor a series of physical signals from human large-scale joint motions and subtle muscle movements. This work provides a new strategy for the development of electronic skins and flexible strain sensors.