Self-healable hydrogels with cross-linking induced thermo-responsiveness and multi-triggered gel–sol–gel transition
Self-healable hydrogels with regulated cross-linking induced thermo-responsiveness (CIT) were prepared from P(N,N-dimethylacrylamide-stat-diacetone acrylamide) P(DMA-stat-DAA), which was synthesized through RAFT copolymerization. The copolymers of P(DMA-stat-DAA) with various compositions were cross-linked by a series of dihydrazide compounds and self-healable hydrogels were prepared without any additional stimulus under neutral conditions. Interestingly, although the copolymer did not show any temperature responsivity, the hydrogels showed thermo-responsiveness with regulated cloud points, which varied with the composition of the copolymer and group ratios of the dihydrazide cross-linkers. With dynamic covalent acylhydrazone bond connections, the hydrogels showed gel–sol–gel transitions regulated by acidity. Also, the gel–sol transition was induced by the addition of excess dihydrazide compounds and the sol–gel transition was triggered by further addition of P(DMA-stat-DAA). The CIT property provided a new method to prepare thermo-responsive hydrogels from non-thermo-responsive polymers, and the catalysis-free self-healable hydrogels with thermo-responsiveness could have great potential applications in areas related to bioscience and biotechnology.