Strong and tough, pH sensible, interpenetrating network hydrogels based on gelatin and poly(methacrylic acid)

Hydrogels are promising materials for biomedical applications due to highly hydrated, porous, permeable structure with possibility to accommodate living cells, drugs, or bioactive factors. In this paper, we reported poly(methacrylic acid) (PMAA)/gelatin IPN hydrogels, synthesized by free-radical polymerization, with adjustable mechanical, structural, physicochemical, and biological characteristics. The influence of methacrylic acid (MAA), gelatin, and cross-linker in the precursor solution on hydrogels properties was investigated. The increasing concentration of MAA, gelatin, and cross-linker led to better mechanical properties, lower porosity, and water content. The compressive mechanical properties of hydrogels were significantly better in comparison to a single-network PMAA hydrogel, while the obtained compressive strength values up to 16 MPa were comparable with tough hydrogels. The increasing concentration of MAA and cross-linker reduced fatigue resistance and degradability, while the increase in gelatin content acted in the opposite way. Swelling tests in different pH conditions demonstrated strong pH-sensibility of the hydrogels, which was more pronounced as MAA concentration was higher, and gelatin and cross-linker concentrations were lower. In addition, the hydrogels strongly promoted the proliferation of human periodontal ligament stem cells and MRC-5 cells as assayed by MTT assay.