Effect of 20-μm-Thin Ceramic Coatings of Hydroxyapatite, Bioglass, GB14 and β-TCP With Copper on the Ingrowth Behavior of Femoral Implants

Aseptic loosening and infection are still the main reasons for revision surgery. The contact of the implant is made through the surface, which is coated with calcium phosphate ceramics for better integration into the bone. The aim of the present work is to optimize these coatings by making them thinner (20 μm) and doping them with copper to add antimicrobial functionality. Four different coating materials were used: hydroxyapatite, Bioglass, GB14, and beta tricalcium phosphate. The coatings were applied by high velocity suspension flame spraying. The titanium rods with the coatings were then implanted bilaterally into the femoral condyles in 144 New Zealand White rabbits, and ingrowth was evaluated after 2, 4, 6, 12, and 24 weeks. Biomechanical (previously published), histological, and histomorphometric analyses were conducted. Histologically, Cu-doped HA, GB14, and β-TCP showed normal ingrowth behavior, with the coating not completely degraded after 24 weeks and remaining in contact with the bone. Bioglass showed rapid degradation and calcium loss from the bone. However, no negative effect of Cu doping on bone cells (osteoblasts, osteocytes and connective tissue cells) was observed. Via histomorphometry, Bioglass showed low bone mineralization, while TCP, HA and GB14 revealed an increase in mineralization over time to values between 70%–95%. Comparable results were obtained with the undoped coatings. The bone-coating contact was in a similar range to the mineralization because of the coating's incomplete degradation after 24 weeks. The thinner coating could also be applied to titanium rods of the same quality (as the titanium plates in Burtscher et al.) using HVFSF. In animal experiments, all rods, regardless of the coating, could be well inserted—there was no delamination. Histology and histomorphometry showed that BG was not suitable for long-term coating as it had already degraded after 4 weeks and also caused calcium loss in the bone. The other coatings were clearly more suitable. However, we also found that still far too much coating remained after 24 weeks because it was too dense.