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

Abstract

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. © 2005 Elsevier B.V. All rights reserved.