Chemical characterization of bioresorbable sol–gel derived SiO2 matrices prepared at protein-compatible pH

Sol–gel derived SiO₂ have been shown to be biocompatible and bioresorbable and they have potential use in living tissue, e.g., in bone regeneration and controlled drug delivery. Bioresorbable SiO₂ is a potential alternative for the controlled delivery of large biologically active agents, such as proteins and peptides. The aim was to prepare SiO₂ matrices with varying bioresorption rate at protein-compatible conditions and to characterize the chemical features of the matrices. SiO₂ was prepared in two morphologies, monoliths by casting and microparticles by spray drying. A model protein was encapsulated into the SiO₂ matrices. Materials were carefully characterized with FTIR- and Raman spectroscopy, TGA-FTIR, solid state ²⁹Si MAS NMR, SEM and matrix dissolution was measured in simulated physiological conditions. It is shown that both fast and slowly dissolving SiO₂ matrices could be prepared at protein-compatible conditions. Fast-dissolving SiO₂ microparticles contained a high proportion of Q³ and a low portion of Q⁴ indicating poor cross-linking of SiO₂ species and an increased amount of hydrolysable terminal groups. Spectroscopic techniques and TGA-FTIR show that organic residues and moisture are left in the matrices. The amount of organic residues is larger in the fast-dissolving SiO₂ matrices, but it does not significantly affect the bioresorption rate.