Biomimetic deposition of silica templated by a cationic polyamine-containing microgel

We report using poly(acrylamide-co-2-(dimethylamino)ethyl methacrylate, methyl chloride quaternized) cationic microgels as a porous colloidal template for biomimetic in situ silica mineralization, allowing the well-controlled synthesis of submicrometer-sized hybrid microgel--silica particles and porous silica particles by subsequent calcination. The microgels were prepared by inverse emulsion polymerization in the presence of a bisacrylamide cross-linker. Silica deposition was achieved by simply stirring an aqueous mixture of the microgel particles and tetramethyl orthosilicate (TMOS) at 20 degrees C for 30 min. No experimental evidence was found for nontemplated silica, which indicated that silica deposition occurred exclusively within the cationic microgel template particles. The resulting microgel-silica hybrid particles were characterized by electron microscopy, dynamic light scattering, FT-IR spectroscopy, 1H NMR and solid-state 29Si magic angle spinning NMR spectroscopy, thermogravimetry, aqueous electrophoresis, and surface area measurements. Aqueous electrophoresis studies confirmed that the hybrid microgel-silica particles had positive zeta potentials over a wide pH range and isoelectric points could be tuned by varying the synthesis conditions. This suggests that these particles could form complexes with DNA for improved gene delivery. The porosity of the calcined silica particles could be controlled by varying the amount of TMOS, suggesting potential encapsulation/controlled release applications.