Mechanical and In Vitro Biological Properties of Hydroxyapatite Bioceramics Reinforced with Strontium-Containing Nano-Bioactive Glass

In this study, different amounts of sol-gel derived strontium-containing bioactive glass nano-powders were added to hydroxyapatite to improve its mechanical properties. The bodies were sintered at 1000-1200 °C. Strontium was used in the bioglass composition for its stimulating effects on bone formation. XRD, SEM and microindentation methods were employed for phase analysis, microstructure observation and microhardness/toughness measurements, respectively. Proliferation and activity of rat-derived osteoblastic cells on samples were also determined using MTT and alkaline phosphatase assays. The results showed that the phase composition of pure hydroxyapatite was not affected by elevating temperature; however, the addition of 1-10% of bioactive glass nano-powder to hydroxyapatite led to the formation of β -TCP phase in which its content increased with bioglass concentration and temperature. In addition to β- TCP, α-TCP and calcium phosphate silicate were also found in the composition of hydroxyapatite sintered with 10% bioglass. Bending strength, microhardness and fracture toughness were improved by adding 1-5% bioglass to hydroxyapatite, whereas a decrease in these mechanical properties was observed by adding 10% bioglass. According to the results, the addition of nano-sized bioglass did not change the rate of cell proliferation, but increased the level of alkaline phosphatase produced.