Mechanical Properties of Chain Silicate Glass Ceramics for Bone Repair

Glass ceramics have many of the properties necessary to construct durable prostheses for bone repair and augmentation. However, their relative lack of clinical success has been associated with poor biocompatibility or difficult processing conditions. New compositions have been developed at Sheffield based on the crystallisation of apatite and chain silicate phases including canasite and potassium-fluorrichterite. Objectives: The aim of this research was to assess the mechanical properties of a range of compositions that can be cast to complex shapes to form osteoconductive custom prostheses for bone augmentation. Methods: Glasses were melted of stoichiometric and modified canasite and potassium-fluorrichterite compositions. Modifications were by the addition of P₂O₅ and (excess) CaO. Heat-treatments were carried out with conventional nucleation and crystal growth schedules. The phase evolution of these modified compositions was characterised using differential thermal analysis, X-ray diffraction and electron microscopy and biaxial flexural strengths tests were performed. Results: All compositions were found to be castable with no sign of devitrification on casting. On heat-treatment the glasses formed chain silicate phases and in the case of P₂O₅ containing glasses, also formed apatite. Flexural strength of 160 MPa was obtained for stoichiometric potassium-fluorricherite, but no values were recorded for stoichiometric canasite due to extremely poor mechanical properties. Improved strengths (220 - 240 MPa) were obtained from the modified compositions. Conclusions: it was concluded that modified apatite-chain silicate glass-ceramics have excellent mechanical strengths compared with materials currently used for bone repair. These results, combined with data from our in vitro and in vivo studies, show that the materials have great potential for production of custom prosthesis for bone tissue repair and augmentation.