Hydrophilic-Hydrophobic-Transition-Triggered Thermosensitive Macroscopic Gel Assembly

Two kinds of poly(N-isopropylacrylamide) (PNIPAAm)-based hydrogels containing -cyclodextrin (-CD) (host gel) and benzyl (guest gel) groups, respectively, are designed and prepared. When mixing the host and guest gels together, due to the presence of the host-guest interaction between the -CD and benzyl groups, a combined hydrogel can be formed at a temperature below the lower critical solution temperature (LCST) via macroscopic self-assembly.When heating this self-assembling system to a temperature above the LCST, the aggregation of the hydrophobic PNIPAAm-based chains pull the -CD and benzyl groups to separate them from each other, leading to the disassociation of the combined hydrogel. Because of the transition from hydrophobic aggregated PNIPAAm-based chains to hydrophilic extended ones as the temperature decreases to a value below LCST, the combined hydrogel can re-form via macroscopic self-assembly between the host and guest gels. The concept of hydrophilic-hydrophobic transition-triggered thermosensitive macroscopic self-assembly can be extended to develop many other stimuli-responsive materials.