A pH-Responsive Hydrogel for Bioactive Self-Healing Cementitious Materials

Bioactive self-healing cementitious materials rely on microbially induced calcium carbonate precipitation to heal microcracks. To facilitate this process, the added microbial cells must be encapsulated in a protective carrier that preserves their viability and metabolic activity within the cementitious matrix. This study reports the synthesis and evaluation of nine pH-responsive superabsorbent hydrogels based on a N,N-dimethylaminoethyl methacrylate (DMAEMA) polymer backbone for this purpose. Three of the DMAEMA hydrogels exhibited pH-dependent swelling within the desired pH range of 8 to 13. One of these hydrogels (N7; DMAEMA:DMAAm:PEGDMA with the molar ratio 10:20:1) showed an exceptional swelling capacity, expanding by 25 times its dry weight at a pH of 8, while exhibiting moderate swelling of 7.5 times at a pH of 13. Moreover, this hydrogel exhibited a highly consistent elastic modulus of 40 kPa, indicating a reproducible polymerization. The in situ radical copolymerization of the N7-hydrogel was biocompatible, and the resulting polymerized gel supported germination and proliferation of endospores of the extremophilic bacterium Clostridium paradoxum within its matrix. The molecular structure of the N7-hydrogel is proposed and supported by Fourier transform infrared spectroscopy (FTIR) and 13C magic-angle spinning (MAS) nuclear magnetic resonance (NMR) data. This novel biocompatible, pH-responsive DMAEMA hydrogel shows strong potential as a carrier for bacterial and chemical healing agents in self-healing cementitious materials.