Hyperbranched polyglycerol hydrogels prepared through biomimetic mineralization

Hyperbranched polyglycerols find increasing usage in biomedicine owing to their excellent biocompatibility like polysaccharides. To prepare hydrogels, they are cross-linked mainly by treating with toxic epoxy reagents. Here we suggest a one-stage nontoxic procedure for the jellification of aqueous solutions that was previously developed for nongelable polysaccharides. It was carried out via the biomimicking mineralization. As the silica precursor, tetrakis(2-hydroxyethyl)orthosilicate containing ethylene glycol residues was employed. It could mineralize directly hydroxyl-containing macromolecules passing a stage of the sol formation. Jellification was performed in one stage in the neutral pH region at the ambient conditions. An organic solvent was not needed because of high hydrophilicity of both the precursor and polyglycerols. An as-prepared hydrogel is ready for applications because of the absence of toxic products. Its structure and mechanical properties were characterized by scanning and transmission electron microscopy as well as dynamic rheology. It was demonstrated that hyperbranched polyglycerols were encased into silica matrix that formed three-dimensional mesoporous network. A study of initial solutions of hyperbranched polyglycerols by the dynamic light scattering revealed their aggregation. This important result was confirmed by direct observations of aggregated macromolecules with high resolution scanning electron microscopy. Entrapped aggregates were also found in the silica matrix.