The influence of hydroxyapatite particles on osteoclast cell activities

Aseptic loosening after total joint arthroplasty is a major problem in orthopedic surgery. Small particles from material wear have been reported as the main cause of implant failure. For this reason, investigation into possible wear particles from the materials used in the implant may lead to longevity after arthroplasty. Hydroxyapatite (HA) has been extensively investigated and reported as an excellent biomaterial with excellent biocompatibility. In this study, we used an in vitro osteoblast/osteoclast model to test the biocompatibility of various-sized HA particles. Primary osteoclasts/osteoblasts were co-cultured with different-sized HA particles (0.5-3.0 μm, 37-53 μm, 177-205 μm, and 420-841 μm) for 3 h, 1 day, 3 days, and 7 days. Cellular responses to the HA particles were evaluated by changes in cell counts and the secretion of transforming growth factor (TGF- β1), alkaline phosphatase (ALP), tumor necrosis factor (TNF-α), prostaglandin (PGE₂), and lactate dehydrogenase (LDH) in the supernatant of the culture media. The results showed that osteoblasts/osteoclasts co- cultured with HA particles smaller than 53 μm undergo the most significant changes. Cellular counts significantly decreased, and the changes were more obvious in the osteoblast population. There also was a significant decrease in TGF-β1 concentration and a significant increase in PGE₂ and LDH concentration, but there were no changes in the TNF-α or ALP titer. It can be concluded that larger HA particles may be quite compatible with bone cells while smaller-sized HA particles can both activate the osteoclasts and decrease the cell population of the osteoblasts. Justification for the additional expense incurred with the use of hydroxyapatite in primary total hip arthroplasty should be further evaluated.