Biocompatibility of defect-related luminescent nanostructured and microstructured hydroxyapatite

Three defect-related luminescent hydroxyapatite (HAP) particles, S1, S2, and S3, with different morphologies (the samples S1 and S2 are nanorods with diameters of 25 nm and lengths of 30 and 100 nm, respectively; sample S3 is bur-like microspheres with diameters of 5-6 μm) were synthesized, and their biocompatibility was investigated by MTT, reactive oxygen species (ROS), interleukin-6 (IL-6), comet, and hemolysis assays. The results indicated that all samples were stable in cell culture medium and did not induce the synthesis of proinflammatory cytokine IL-6 or result in hemolysis. It was found that samples S1 and S3 inhibited osteoblast (OB) viability at concentrations of 5, 10, 20, 40, and 80 μg/mL for 24, 48, and 72 h. Sample S2 had no effect on the viability of OB at all tested concentrations for 24 and 48 h, but the viability of OB was increased at concentrations of 20, 40, and 80 μg/mL for 72 h. Samples S1 and S3 could increase the level of cellular ROS; sample S2 had no effect on the level of cellular ROS at a concentration of 20 μg/mL for 48 h. Although samples S1 and S3 induced significant DNA damage, sample S2 could not cause significant DNA damage at a concentration of 20 μg/mL for 72 h. The results suggest that longer nanorod HAP can show excellent biocompatibility and therefore may find potential applications in biomedical fields.