Robust Hydroxyapatite Coating by Laser-Induced Hydrothermal Synthesis

Owing to enhanced biocompatibility and osseointegration, hydroxyapatite (HAp) coatings are often applied to biomedical devices that are implanted directly on the bone. Although various HAp coating techniques have been developed, they are restricted due to the time-consuming HAp synthesis and additional coating processes. Herein, the development of a rapid single-step method for simultaneous synthesis and coating of HAp via nanosecond laser surface treatment is described. In the conventional HAp-coating method, the resulting interface between the HAp layer and the base material is clearly distinguished. However, in this method, HAp synthesis and coating occur simultaneously via the melting of the base material (i.e., titanium, polyetheretherketone, and polycaprolactone) to form a gradient HAp-base material composite coating layer. The resultant coating layer on a titanium surface exhibits a binding force of 31.7–47.2 N, which is sufficient for medical implant applications. Changing the laser irradiation conditions provides quantitative adjustment of the HAp formation process and coating layer thickness. Furthermore, the resulting HAp coating layer better facilitates the attachment of bone cells. These results offer a breakthrough in the surface treatment of bone-bonding sites of metal and polymer biomedical devices.