In Situ Formation of Thermosensitive PNIPAAm-Based Hydrogels by Michael-Type Addition Reaction

To investigate the possibility of in situ thermosensitive hydrogel formation via Michael-type addition reaction, we designed and prepared thiol- and vinyl-modified poly(N-isopropylacrylamide) (PNIPAAm)-based copolymers. When the solutions of these two kinds of PNIPAAm-based copolymers were mixed at physiological temperature (37 degrees C), a physical gelation resulting from the hydrophobic aggregation of PNIPAAm based copolymers and chemical cross-linking between thiol and vinyl functional groups or so-called chemical gelation occurred, resulting in the formation of a three-dimensional hydrogel. Because all the gelations were performed at a high temperature (above LCSTs of the PNIPAAm based copolymers), these in situ formed hydrogels presented heterogeneous network structures, resulting in an improved thermosensitivity in comparison with the conventional one.