Structural and Mechanical Properties of Bioactive Glass–Ceramic Composites

Abstract

Bioactive glass–ceramic composites based on biogenic hydroxyapatite or synthetic calcium phosphates mixture with addition of sodium borosilicate glass (31.5 wt.%) are prepared using one-stage sintering at a temperature of ≤800°C. The comparative analysis of the structure and physical–mechanical properties of the composites produced is carried out. It is established that hydroxyapatite keeps the phase composition (Ca₅(PO₄)₃(OH)) during sintering the composites based on biogenic hydroxyapatite. During sintering the composites based on a mixture of synthetic phosphates, a phase transformation and interaction of phosphates with glass phase occur. This results in the formation of glass ceramics, which contain: calcium silicates (wollastonite CaSiO₃), sodium–calcium silicates (silicate-germanate Na₂Ca₂(SiO₃)₃ and melilite Na₂Ca₆(Si₂O₇)(SiO₄)₂), sodium borate (Na₃ВO₃), and hydroxyapatite (Са₅(РО₄)₃(ОН)). The analysis of porous structure of glass ceramic composites showed a significant difference in the pore size distribution depending on the material composition. The difference in the surface and fracture structure for both types of composites is established. It is shown that mechanical properties of the composites based on biogenic hydroxyapatite are higher compared to the composites based on synthetic calcium phosphates at similar total porosity value (32.5–34.5%). This may be due to the phase transformations and interaction of phosphates with glass during sintering and the formation of a complex silica structure. It is established that the strength of the composites produced is comparable to the strength of the native bone.