Add time:07/13/2019         Source:sciencedirect.com

Redox/temperature responsive poly(N-isopropylacrylamide/N-hydroxyethylacrylamide) (P(NIPA/HEAA)) nonionic nanogels (NP-BAC) crosslinked with N,N′-Bis(acryloyl)cystamine (BAC) have been prepared. An analogous nanogel incorporating N,N′-methylenebisacrylamine (BIS), a reduction-insensitive nanogel (NP-BIS), was chosen as a control nanogel. Compared to the nondegradable NP-BIS nanogel, NP-BAC nanogel particles were found to swell and become less dense due to cleavage of disulfide bonds in BAC. Interestingly, the NP-BAC nanogels preserved their spherical shape after reduction. When loaded with the drug propranolol, NP-BAC nanogels showed accelerated drug release in the presence of 1,4-dithiothreitol (DTT), with rate of release controlled by the DTT concentration. Furthermore, the liquid-crystal-glass phase behavior of these nanogel suspensions were investigated relative to polymer concentration and temperature. Following the liquid-crystal-glass phase diagram, these nanogels can be fabricated into hydrogel by crosslinking with divinylsulfone (DVS). These crosslinked hydrogels exhibited optical diffractions sensitive to temperature and DTT concentration. Several unexpected and distinguishing differences between NP-BAC and NP-BIS nanogels were noted. For example, NP-BAC nanogel formed colloidal crystalline structures faster than NP-BIS nanogels and their reflection signals were much stronger. The reflection peaks of NP-BAC crosslinked hydrogel were blue shifted with rising temperature while that of NP-BIS hydrogel remained unchanged.

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