Silicon-zinc-glycerol hydrogel, a potential immunotropic agent for topical application.

Nanoparticles synthesized using sol-gel method are promising agents for biomedical applications, in particular for the therapy and diagnosis of various diseases. Using silicon and zinc glycerolates as biocompatible precursors we synthesized by the sol-gel method a new bioactive silicon-zinc-containing glycerohydrogel combining the positive pharmacological properties of the precursors. In the present work the structural features of silicon-zinc-containing glycerohydrogel and its immunotropic properties were studied. The advanced physical methods, including XRD, TEM, dynamic and electrophoretic light scattering, were used for studying the structural features of the gel. Hydrolysis of zinc monoglycerolate was investigated under gelation conditions. Evaluation of the efficiency of silicon-zinc-containing glycerohydrogel in providing immune functions was carried out using a model of the complicated wound process behind immunosuppression induced by hydrocortisone administration in the Wistar rats. It has been shown that zinc monoglycerolate exists in the state of amorphous nanoparticles in the cells of 3D-network formed due to incomplete hydrolysis of silicon glycerolates and subsequent silanol condensation. Zinc monoglycerolate is not hydrolyzed and does not enter 3D-network of the gel with the formation of Zn-O-Si groups, but it forms a separate phase. Immunotropic action of silicon-zinc-containing glycerohydrogel was revealed by the histology and immunohistochemistry methods. Amorphous nanoparticles of zinc monoglycerolate, water-soluble silicon glycerolates, and products of their hydrolytic transformations, which are present in a aqueous-glycerol medium, are in the first place responsible for the pharmacological activity of hydrogel. The results obtained allow us to consider silicon-zinc-containing glycerohydrogel as a promising immunotropic agent for topical application.

Mechanism of structural networking in hydrogels based on silicon and titanium glycerolates.

Formation of organic/inorganic hydrogels based on silicon- and titanium-glycerol precursors synthesized by transesterification of alkoxy derivatives in excess of glycerol was investigated. The precursors in excess of glycerol and obtained gels were studied by chemical and physical methods including gelation kinetics, IR spectroscopy, XRD, dynamic and electrophoretic light scattering, mechanical deformation, which disclosed the basic difference in the gelation mechanism and structure of network in the hydrogels. Due to this difference, the gelation time of silicon- and titanium-glycerol precursors depended on pH or electrolyte addition in an opposite way. In the wide pH range, silicon-glycerol hydrogel was a polymeric single-phase system formed by the polymeric network homogeneously swollen in liquid water/glycerol medium. Flory-Rehner theory applied to the elastic modulus of these gels gave 40-180 monomer base units in the subchains of the network depending on water content in the gel. The mechanism of networking was three-dimensional polycondensation promoted by the electrically charged functional groups attached to the flexible polymeric chains. Electrolyte solutions provided the gelation according to Hofmeister series. Titanium-glycerol hydrogels were heterogeneous colloid systems at pH>1.5 and single-phase polymeric gels at lower pH. Electrolyte solutions provided the gelation according to Schultze-Hardy rule.