Chapter 21: Sol–Gel-Derived Glasses for Bone Tissue Engineering

Bone repair and replacement is a major health concern affecting millions of people worldwide. Although traditional melt-quench silicate-based bioactive glasses have shown promise in treating some of these defects, an alternative glass processing method, the sol–gel process, creates glasses that allow for a quicker, more tailored approach to bone tissue repair. This technique typically uses metal alkoxide precursors that react to form a sol, then produce a gel, which is then calcined yielding a glass possessing a high surface area and porosity. These textural properties can be controlled through processing, allowing for rapid conversion to hydroxy-carbonate apatite (HCA). Furthermore, it is possible to adjust the glass composition to incorporate metallic ions, as well as drugs, post calcination for targeted therapeutic effects. Additionally, the liquid nature of the process serves as a flexible starting point to fabricate different forms including three-dimensional foams, fibres, and ordered mesoporous glasses which greatly expand the range of therapies of these glasses including drug delivery and customized implant shapes. The sol–gel process also serves as a starting point for producing coatings that can improve the biocompatibility and bioactivity of the materials. As an alternative to silicate-based sol–gel systems, those based on borate have recently been developed and have demonstrated unprecedented times for conversion to HCA. This chapter provides an overview of the sol–gel-derived glasses and their applications in bone tissue engineering.