Immunomodulatory effect of electrodeposited calcium phosphate coatings on early inflammatory response to bone implant

Host cells response to biomaterials is crucial for implant long-term integration in bone site. Calcium phosphate coatings, particularly hydroxyapatite (HA) coatings, have improved the biological properties and osseointegration of titanium implants. However, progress still needs to be made in better controlling the risk of aseptic loosening, which is mainly associated with uncontrolled inflammatory reaction near the implant. Calcium-deficient hydroxyapatite (CDHA) has demonstrated superior bioactivity and in vivo performance compared to HA. The aim of this work was to determine in vitro the effects of three different implant surfaces, etched titanium alloy, HA-coated titanium and CDHA-coated titanium on the early inflammatory response of human primary monocytes and their differentiation into osteoclasts as a predictor of implant fate. ELISA and RT-qPCR evidenced a higher cytokine response (IL-8, TNF-α, IL-1β, IL-6) with HA compared to CDHA. Zymography experiments revealed a moderate MMP-9 proteolytic profile with CDHA, which could be conducive to bone remodeling around the implant. No increased osteoclastogenesis was observed in the presence of both coatings, indicating that immune cell activation does not necessarily lead to osteoclast-mediated bone degradation. This study showed that CDHA coating on a titanium implant elicits a more suitable immune response than standard HA coating, reducing the risk of inflammatory osteolysis. These data also highlighted the need to consider the whole peri-implant environment for accurate implant prognosis.