Controllable stabilization of poly(N-isopropylacrylamide)-based microgel films through biomimetic mineralization of calcium carbonate

Two types of thermoresponsive microgels, poly(N-isopropylacrylamide) (PNIPAM) microgels and poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAMAC) microgels were synthesized and used as templates for the mineralization of amorphous calcium carbonate (ACC) by diffusion of CO2 vapor under ambient conditions. Thermosensitive PNIPAM/CaCO3 hybrid macroscopic hydrogels and micrometer-sized PNIPAMAC/CaCO3 hybrid microgels were controllably obtained and different mineralization mechanistic processes were proposed. The impact of the loaded CaCO3 on the size, morphology, stability, and thermosensitivity of the microgels was also analyzed. PNIPAM/CaCO3 hybrid macrogels had a slight decrease in thermoresponsive phase transition temperature, while PNIPAMAC/CaCO3 hybrid microgels showed a clear increase in phase transition temperature. The difference reflected different amount and location of ACC in the gel network, causing different interactions with polymer chains. The PNIPAMAC/CaCO 3 microgels formed stable monolayer films on bare silica wafers and glass coverslips upon drying. The microgel films could facilitate the attachment and growth of 3T3 fibroblast cells and their subsequent detachment upon temperature drop from 37 °C to the ambient condition around 20 °C, thus, offering a convenient procedure for cell harvesting. © 2012 American Chemical Society.