Bioactive glass scaffolds for the regeneration of load-bearing bone

Biocompatible scaffolds that replicate the structure and function of bone would be ideal bone substitutes for structural bone loss, provided they have the requisite mechanical properties for reliable long-term loading. In this dissertation, strong porous scaffolds of silicate 13-93 bioactive glass, created with two different microstructures, were evaluated to determine their mechanical properties and their capacity to regenerate bone in a rat calvarial defect model. Scaffolds with an oriented microstructure of columnar pores were prepared by unidirectional freezing of camphene-based suspensions, followed by thermal annealing and sintering. By optimizing the freezing conditions, annealing time, and sintering temperature, constructs (porosity = 50 ± 4%; average pore diameter = 100 µm) were created with a compressive strength of 47 ± 5 MPa and an elastic modulus of 11 ± 3 GPa (in the orientation direction). New bone formation in the pore space of the scaffolds increased from 37% at 12 weeks to 55% at 24 weeks in vivo. Scaffolds with grid-like microstructure (porosity= 47 ± 1%; pore width = 300 µm), prepared by a robotic deposition (robocasting) technique, had a compressive strength (86 ± 9 MPa) and an elastic modulus (13 ± 2 GPa) comparable to human cortical bone, a Weibull modulus of 12, and excellent fatigue resistance in compression. Bone regeneration in the as-fabricated scaffolds in vivo (32% at 6 weeks) was significantly enhanced (to ~60%) by a surface treatment in an aqueous phosphate solution or loading the surface-treated scaffolds with bone morphogenetic protein-2 (1 µg/defect), prior to implantation. Scaffolds of 13-93 bioactive glass with a grid-like microstructure prepared by robocasting, showing better mechanical properties and a greater capacity to support bone formation, are more promising in structural bone repair --Abstract, page iv