Effect of silica precursor transformation on diclofenac sodium release

The present paper describes the preparation of a new type of ternary composite where pure silica gel or polysilsesquioxane was deposited on a polymer carrier loaded with a high dose of diclofenac sodium. The silica species were prepared by in situ gelation of the precursors, tetraethoxysilane (TEOS) or ethyltriethoxysilane (ETEOS), in the presence of an acidic catalyst in the vapour phase. The conducted studies (low temperature nitrogen sorption, XRD, SEM, EDX) reveal that the introduction of drug molecules, as well as silica species, significantly changes the internal structure of the host material. The total porosity of the ternary composites strongly depends on the type of applied silica precursor. Additionally, it is shown that the exposure of the TEOS-saturated or ETEOS-saturated solid dispersion of drug within the polymer to acid vapors is sufficient to cause the irreversible transformation of diclofenac sodium into sodium chloride and a derivative of phenylacetic acid. Furthermore, TEOS prevents the transformation of the drug into its acidic form more effectively than the ETEOS precursor. Finally, the in vitro release of the drug is demonstrated, which clearly indicates that after the embedding both of the silica species, the rate of drug release is modified and the degree of initial drug delivery is successfully diminished. The obtained data are analyzed using different kinetics models to give insight into the possibility of prolonged release of a drug and the probable mechanism of drug release from the investigated samples.