Effects of the doping concentration of boron on physicochemical, mechanical, and biological properties of hydroxyapatite

Ion doping is an approach to modify properties of materials, like hydroxyapatite (HA), that contributes to designing biomaterials with desired characteristics applicable in bone defect treatments. Recently, boron (B) has been noticed in biomaterial fields due to its beneficial effects on formation, growth, and quality of bone. In this study, B-doped HA nanoparticles with different molar concentrations of B (0.05, 0.1, 0.25, and 0.5) were synthesized through microwave-assisted wet precipitation. The effects of B content on various properties of HA were evaluated. The results demonstrated that the size of HA particles reduced from 106 nm to 89-85 nm in B doped materials. Meanwhile, the crystallinity degree of B doped HA (BHA) samples was between 89.90% and 93.77%, compared to 95.19% of HA. Diametral tensile strength of samples was measured in the ranges of 2.51 and 3.61 with no significant difference among groups. The micro-hardness of HA was 0.88 GPa, whilst doped ones had hardness values of 0.5 GPa-0.68 GPa. Biodegradability of samples increased from less than 1% to approximately 4% after 28 days, while B-doping did not make any change in the degradation rate. Doping dosages were appropriate in terms of bioactivity and cell viability, and B doping caused higher bioactivity and cell proliferation. All changed properties were dose-dependent and more effective in doped groups with a higher amount of B. Despite proliferative effect, <= 260 mu g/l and 770 mu g/l of B release in two groups with the highest dopant concentrations did not positively influence the osteogenic activity of cells. Our results demonstrated that doping concentrations that resulted in B release & LE;260 mu g/l seem more appropriate dosage, especially for bone tissue engineering and substitute applications due to promoted bioactivity and proliferation, as well as no obstructive effects on mechanical properties and osteogenic activities of HA.