In vitro and in vivo demonstration of physically and chemically in situ gelling NIPAAm-based copolymer system

Poly(NIPAAm-co-hydroxyethylmethacarylate (HEMA)) acrylate and poly(NIPAAm-co-cysteine ethyl ester (CysOEt)) were synthesized and characterized by GPC(gel permeation chromatography), rheology, NMR (nuclear magnetic resonance), and Ellman's method. Upon mixing of these materials in aqueous solution, they formed gels immediately at body temperature owing to temperature-driven physical gelling, and gradually cured by chemical cross-linking through Michael-type addition reactions between thiols and acrylates. The rate of nucleophilic attack in the Michael-type addition reaction was shown to be highly dependent on the mole ratio of thiol to acrylate at neutral pH. Physical and chemical gelation improved the mechanical properties of the materials compared to purely physical gels. In vitro and in vivo results revealed that chemical and physical gels formed stiffer less viscoelastic materials compared to purely physical gels. Physical and chemical gel systems using thermosensitive polymer with acrylates and thermosensitive polymer with thiols showed minimum toxicity.