Thermoresponsive microgel decorated with silica nanoparticles in shell: Biomimetic synthesis and drug release application

We report designing and using a thermoresponsive microgel, poly(N-isopropylacrylamide-co-2-(dimethylamino) ethyl methacrylate, methyl chloride quaternized) (poly(NIPAM-co-DMC)) as a colloidal and biomimetic template for silica deposition, producing a microgel decorated with particulate silica in shell. Poly(NIPAM-co-DMC) microgel was synthesized by surfactant-free emulsion polymerization, showing a lower critical solution temperature (LCST) of about 34 °C estimated by dynamic light scattering (DLS) measurements. The silicification selectively occurred in the shell domain of microgel, due to that the DMC segments enriched in microgel shell are catalysis-active for silica deposition under ambient conditions. DLS studies did not show significant size change of hybrid microgel-silica particles with temperatures from 20 to 50 °C, indicating the remarkable suppression of LCST of precursor microgel due to silica deposition. We further found that the silica deposition could be well controlled by simply adjusting the level of silica source and the time for silica deposition. The higher level of TMOS amount and longer time for silica deposition produced the silica-microgel particles with much denser and thicker silica-rich shell. Moreover, the drug-delivery behaviors of poly(NIPAM-co-DMC) microgel and hybrid microgel-silica particles were studied by selecting aspirin as a model drug. The preliminary data indicate that the drug release has been remarkably retarded after silica deposition on the shell of microgel.