Protein encapsulation in functionalized sol–gel silica: influence of organosilanes and main silica precursors

Over the last few years, bone repair has increasingly gained in importance. In recent years, considerable attention has been given to the administration of therapeutic biomolecules to promote tissue regeneration. The aim of this work is the study of the influence of functional groups present at the surface of silica pores on the release kinetics of a model protein (i.e. Soybean Trypsin Inhibitor, STI). The carried protein was examined via: (i) the impregnation of silica gels in the protein solution after the silica gel drying and/or calcination (i.e. impregnation method), and ii) the direct incorporation of the protein during the silica gel synthesis (i.e. in situ method). Surface chemistry and textural properties were tuned using different organosilanes (i.e. functionalized silanes containing amine, ethylene diamine, or phenyl groups) and different main silica precursors (i.e. containing methoxy or ethoxy groups). These physicochemical modifications were shown to deeply affect the immobilization and release kinetic of STI. In particular, for both encapsulation methods, phenyl-modified samples presented a high amount of encapsulated STI accompanied by a very low release of STI over the 85-day period. The other functional groups gave rise to a lower encapsulation yield. Regarding the protein release profiles, a fast release of STI was observed for the samples prepared via the impregnation method, which showed a burst effect followed by a sustained release until day 30. On the opposite, the in situ method allowed a better control of the release rate of this protein over the first 24 h followed by a sustained released up to 85 days.