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

Abstract

Although wearable sensors based on polymer hydrogels have great progress, achieving biocompatibility, long-term 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(ClO4)2 hydrogel presents a high ionic conductivity of 13.58 S m−1 at 25 °C. The re-prepared hydrogel demonstrates outstanding anti-freezing properties, even at −45 °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 freeze-dried PD3M7/4 M Zn(ClO4)2 gel can recover up to 89.5 % of the original water content after 96 h at 20 % RH and 25 °C. Importantly, the wearable strain sensor based on PD3M7/4 M Zn(ClO4)2 hydrogel shows high sensitivity (7.43 kPa−1 at 25 °C and 4.83 kPa−1 at −45 °C), ultra-low detection limit (30 Pa), outstanding cycle stability (10000 cycles), and quickly responds to human movement detection at 25 °C and −45 °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.