A biocompatible, highly adhesive zwitterionic polymer hydrogel with high ionic conductivity, anti-freezing and moisturizing for wearable strain sensor

Although wearable sensors based on polymer hydrogels have great progress, achieving biocompatibility, longterm stability, and being used in harsh environments for polymer hydrogels remains a significant challenge. In this work, a new simple tactic is proposed to prepare biocompatible zwitterionic polymer hydrogels (PDM) by copolymerization of dopamine acrylamide (DAA) and 2-methacryloyloxyethyl phosphorylcholine (MPC). The synergistic effects of the Hofmeister and electrostatic interaction effect based on a series of inorganic salts on PDM hydrogels are studied. The PD3M7/4 M Zn(ClO 4 ) 2 hydrogel presents a high ionic conductivity of 13.58 S m -1 at 25 degrees C. The re -prepared hydrogel demonstrates outstanding anti -freezing properties, even at -45 degrees C, the hydrogel exhibits transparency and flexibility, and the ionic conductivity is up to 1.81 S m -1 . Moreover, the hydrogel has excellent adhesive strength (34.7 kPa), and anti -dehydration (94.4 % after 30 days). The freezedried PD3M7/4 M Zn(ClO 4 ) 2 gel can recover up to 89.5 % of the original water content after 96 h at 20 % RH and 25 degrees C. Importantly, the wearable strain sensor based on PD3M7/4 M Zn(ClO 4 ) 2 hydrogel shows high sensitivity (7.43 kPa -1 at 25 degrees C and 4.83 kPa -1 at -45 degrees C), ultra -low detection limit (30 Pa), outstanding cycle stability (10000 cycles), and quickly responds to human movement detection at 25 degrees C and -45 degrees C. This work provides an effective strategy to prepare the hydrogel which will be more appropriate to apply in wearable sensors and biological tissue engineering.