Laser cladding preparation of HA-Ag gradient bioactive ceramic coating: A feasibility study

Abstract Laser cladding is one of the most potential techniques to prepare hydroxyapatite (HA) bioactive ceramic coating on titanium (Ti) surface to enhance bioactivity of orthopedic implants. However, there exists a disadvantage that HA is easy to be decomposed due to laser overheating for melting Ti metal or converted into a non-bioactive substance due to chemical reaction with Ti metal. In this paper, a novel technique for preparing a higher bioactive ceramic coating with a three-layer gradient structure on medical Ti substrate surface by wide-band laser cladding process was proposed. Firstly, a silver (Ag) barrier layer was prepared on Ti substrate by using 100 wt% Ag powder, which was used to block the diffusion of Ti element to the coating, so as to avoid the chemical reaction between HA and Ti to generate non-bioactive calcium titanate (CaTiO3). Secondly, a transition layer was prepared in the middle by using the powder mixture of HA and Ag in weight ratio of 3:1 as the cladding material on the barrier layer. Finally, a HA bioactive ceramic layer was prepared on the transition layer at lower laser power density by using 100 wt% HA powder, which could help to create osseointegration between the coating and the host bone tissue. The morphology, phase compositions of the three functional layers of the HA-Ag bioactive ceramic coating were investigated, and their formation mechanisms were analyzed. The bioactivity and biocompatibility of the coating were assessed respectively by simulated body fluid (SBF) immersion test and cell culture test in vitro. The results showed that the main phase of the bioactive layer of the gradient coating was HA, which exhibited excellent bioactivity and biocompatibility. The proposed method of bioactivity modification for Ti metal implant surface is feasible, which has a good prospect for bone tissue engineering applications.