Unique Self-Reinforcing and Rapid Self-Healing Polyampholyte Hydrogels with a pH-Induced Shape Memory Effect

Tough polyampholyte hydrogels have attracted large attention owing to their favorable mechanical strength, shape memory, and self-healing properties. However, traditional tough polyampholyte hydrogels only have salt responsiveness, and the self-healing usually takes a long time or needs extra treatments. Moreover, self-reinforcement of the hydrogels is essential for the hydrogels during use after the preparation process. In the present work, a weak cationic monomer is introduced to the polyampholyte hydrogel system and copolymerized with a strong cationic monomer and strong anionic monomer with an equal mole ratio between total cationic monomers and anionic monomers. The hydrogel can fix the temporary shape in HCl solution and recover to the original shape in NaOH solution. Interestingly, the hydrogel shows a self-reinforcement capability and the tensile strength increases continuously to ten times larger than that of the as-prepared one by alternately immersing in HCl and NaOH solutions, which presents a new strategy to strengthen the polyampholyte hydrogel. Moreover, the hydrogel exhibits a rapid self-healing capability within S min just by making contact without any extra treatment. Healable simulated blood vessels and conductive hydrogel devices are designed consequently. The present polyampholyte hydrogel with shape memory, self-reinforcement, self-healing, and electroconductivity provides a novel strategy for developing new materials in the fields of wearable electronics, flexible devices, and soft robotics.

Automated summary

The introduction of a weak cationic monomer into the polyampholyte hydrogel system, along with copolymerization with a strong cationic monomer and strong anionic monomer, enhances the self-healing and self-reinforcement capabilities of the hydrogel. The hydrogel can fix a temporary shape in HCl solution and recover to its original shape in NaOH solution. Through alternating immersion in HCl and NaOH solutions, rapid self-healing and increased tensile strength can be achieved within a few minutes.