Switchable on/off drug release from gold nanoparticles-grafted dual light- and temperature-responsive hydrogel for controlled drug delivery.

A switchable dual light- and temperature-responsive drug carrier using gold nanoparticles (Au NPs)-grafted poly(dimethylacrylamide-co-acrylamide)/poly acrylic acid [P(DMA-co-AAm)/PAAc] hydrogel was prepared by free radical polymerization procedure using N,N-methylenebisacrylamide as cross-linker and ammonium persulfate as initiator. Initial P(DMA-co-AAm) hydrogel and uniformly-distributed stable Au NPs, prepared by reduction of hydrogen tetrachloroaureate (III) hydrate in the presence of trisodium citrate, were synthesized separately. Then, the prepared P(DMA-co-AAm) and Au NPs were added to an acrylic acid solution along with the cross-linker and initiator to prepare PAAc hydrogel within the mixture. This improves the swelling ratio and stabilizes Au NPs in networks. Furthermore, a cross-linked P(DMA-co-AAm-co-AAc) random hydrogel was also prepared with the same monomer compositions as the above hydrogel for comparison of their properties. Then, swelling, thermal sensitivity and thermal and optical switching properties of the prepared hydrogels were investigated in two acidic (pH=1.2) and neutral (pH=7.4) buffered solutions to simulate stomach and intestine body conditions. Finally, loading and cumulative release (%) of ofloxacin antibiotic as model drug were considered in both thermal and optical switching conditions. Based on these results, pulsatile release vehicle was obtained which have the "on" state at higher temperatures and the "off" state at lower temperatures.