UV-induced gelation on nanometer scale using liposome reactor

A protocol for preparation of polymer hydrogel spherical particles on a nanometer scale (nanogels) was developed. The protocol includes encapsulation of hydrogel-forming components into liposomes, UV-induced polymerization within the liposomes, solubilization of the lipid bilayer by detergent, removal of the phospholipid, detergent molecules, and their micelles by dialysis, and drying nanogels by evaporation in a temperature gradient. Dynamic light scattering technique was employed to characterize the size distribution of poly(acrylamide), poly(N-isopropylacrylamide), and poly(N-isopropylacrylamide-co-1-vinylimidazole) hydrogel particles. Hydrophobic chains of N-octadecylacrylamide were immobilized onto the surface of the poly(N-isopropylacrylamide-co-1-vinylimidazole) hydrogel particles to use them as anchors for attaching the nanogels onto the lipid bilayers. The diameter of the nanogels prepared varied between 30 and 300 nm. The solvent, temperature, and pH sensitivities of the liposomes, nanogels, and their mixtures were studied, It was found that the phospholipid bilayer always coats the surface of both unanchored and anchored hydrogel particles upon mixing. Aggregation of the lipid bilayer-coated nanogels (lipobeads) was observed when the gel particles collapsed. The mechanism of aggregation differs for the lipobeads containing unanchored cores and those containing anchored hydrogel cores. The hydrogel-liposome structures of a nanometer size are of potential importance for applications such as biomimetic sensory systems, controlled release devices, and multivalent receptors.