Kozakevych R. Composites based on silica and chitosan for controlled release of active substances

Adsorption of diclofenac from ethanol on the surface of hydrated, methylated and aminated silicas was found to has a monolayer character and is described by Langmuir's model. In the presence of grafted amino groups on the surface, adsorption capacity of silica is increased due to formation of salt-type bonds with carboxyl groups of diclofenac. The highest values of diclofenac adsorption on the surface of hydrated silica were achieved in experiments with the solutions of active compound in acetic acid. At impregnation of porous silica matrix with diclofenac solutions the supported active substance exists in the amorphous state which invokes an increase of its dissolution rate. Rate of diclofenac release depends on the porous structure of carriers and is decreased with pore diameter diminution due to diffusion mechanism of the diclofenac release in such systems. A method of the polymeric granules formation for protonated chitosan was elaborated. It was shown that rate of diclofenac release from polymeric spheres is decreased in accordance with the following sequence: deprotonated chitosan > chitosan crosslinked with glutaraldehyde > protonated chitosan. It was demonstrated that release of the active component from composites based on silica and chitosan can be controlled by means of modification of the inorganic carrier surface chemistry. Introducing hydrophilic silica into polymeric granules increases the active substance release rate, whereas in composites containing hydrophobic silica desorption of diclofenac is significantly decreased.