Thermo-responsive hydrogels with nanodomains: Rapid shrinking of a nanogel-crosslinking hydrogel of poly(N-isopropyl acrylamide)

Rapidly shrinking poly(N-isopropyl acrylamide) (PNIPAM) hydrogels are prepared by crosslinking with self-assembled nanogels that consist of cholesteryl- and methacryloyl-substituted pullulan (CHPMA). The CHPMA nanogel (R_h = 26.4 nm) was used as a crosslinker for a hydrophilic nanodomain. Transmission electron microscopy images of the nanogel-crosslinked PNI-PAM hydrogel reveal a well-defined nanoporous structure. The nanogel-crosslinked PNIPAM hydrogel shows rapid shrinking based on its structure. The shrinking half-time was ≈2 min, which is about 3400 times faster than that of a PNIPAM hydrogel crosslinked by methylene(bisacrylamide).