A responsive poly(N-isopropylacrylamide)/poly(ethylene glycol) diacrylate hydrogel microsphere

A responsive hydrogel microsphere, which is constituted by poly(N-isopropylacrylamide)/poly(ethylene glycol) diacrylate, was fabricated in an aqueous two-phase system based on the polymer–polymer immiscibility. Characteristics of the hydrogel microsphere, such as the particle size and the morphology of freeze-dried or hydrated natural microspheres in water, tetrahydrofuran (THF)/H₂O (1:1 in volume) or acetone/H₂O (1:1 in volume), were investigated. The results showed that the swelling ratio and the particle size of the hydrogel microspheres were highly dependent on solvent composition. In addition, these characteristics were dramatically reduced when THF or acetone was added into the aqueous media. Scanning electron microscopy and environmental scanning electron microscopy micrographs also visually demonstrated that the regular spherical shape of the microspheres in water turned to irregular in shape when the microspheres were immersed in THF/H₂O or acetone/H₂O mixtures instead of pure water.