Highly transparent, self-healing, injectable and self-adhesive chitosan/polyzwitterion-based double network hydrogel for potential 3D printing wearable strain sensor

A purely physically crosslinked double network (DN) hydrogel, poly(sulfobetaine-co-acrylic acid)/chitosan-citrate (P(SBMA-co-AAc)/CS-Cit) DN hydrogel, was prepared based on electrostatic interaction and hydrogen bonding between the polymer chains. The hydrogel is highly stretchable, transparent, anti-fatigue, self-adhesive and has good self-healing properties with a self-healing efficiency as high as 95.4%. Furthermore, the resistance of the P(SBMA-co-AAc)/CS-Cit DN hydrogel is sensitive to a wide strain window and the relative resistance shows stable and reliable change during deformation. Herein, the hydrogel was demonstrated as a strain sensor to detect human motions, such as joint bending and swallowing. More excitingly, before ionic crosslinking, the P(SBMA-co-AAc)/CS-Cit composite hydrogel is injectable, thus the P(SBMA-co-AAc)/CS-Cit DN hydrogel sensor can be made into various complex shapes by injecting the P(SBMA-co-AAc)/CS-Cit composite hydrogel into citrate solution, including multilayer structures, exhibiting a great potential for applications as 3D printing strain sensors.