Excipient adjusting rheological properties of silica-based injectable hydrogel composites for controlled drug delivery

Aims: The aim of this study was to prepare different silica-based hydrogel composites and to study how the amount and type of silica particles - both with and without embedded APIs - can be varied in presence of alginate in the hydrogel composites, and its influence on the rheological properties and dissolution rates.

Materials and methods: Silica microparticles with and without encapsulated levothyroxine were manufactured from alkoxide hydrolysis and spray drying to be subsequently mixed with silica hydrogel in the presence and absence of small amounts of sodium alginate. The resulting material was treated under in-sink conditions to evaluate the dissolution rates. In addition, the obtained material was tested for rheology and injection force measurements.

Results: The findings demonstrate that alginate facilitates the reduction of silica microparticle concentration while maintaining injectability and modulating dissolution rates, thereby enhancing formulation tunability. Furthermore, alginate improved the rheological characteristics and injection performance of composites containing levothyroxine-loaded silica microparticles, which otherwise posed injection difficulties.

Conclusions: The study had shown that alginate contributes to the formation of more homogeneous hydrogel silica composites under shear stress, supporting its potential as a functional excipient in advanced drug delivery systems.

Silica microparticles; controlled release; injection force; rheology; silica hydrogel; sodium alginate.