Pulsed Laser Deposition of crystalline hydroxyapatite coatings for biomedical implant coatings

Biomedical implants are getting abundant as the demand for implant surgeries is increasing. Stainless steel 316L, titanium alloys, and cobalt chromium are the most commonly used materials for biomedical implants. However, human bodies occasionally react to these materials as "foreign bodies" due to their insufficient bioactivity. Although coating them with hydroxyapatite (HAP), Ca₁₀(PO₄)₆OH_2, has been a mainstream approach for making bioinert metal surfaces biocompatible, obtaining both mechanically stable and bioactive HAP layers has been a challenge. Part of the problem lies in producing crystalline coatings as they have better degradation resistance in saline human body fluid. In this work, the production of crystalline HAP films prepared by pulsed laser deposition technique was investigated with an emphasis on degradation resistance in the human body, film-implant adhesion strength, and bioactivity properties. Our XRD results confirm that two methods can be used to obtain crystalline films: varying the substrate temperature from 25 to 800 or post-deposition annealing in an air environment. In addition, the effect of laser wavelengths: 1064, 532, and 355 nm on film microstructure and mechanical qualities were studied via SEM with EDX analysis, AFM, pull-out, and nanoindentation tests. Lastly, the bioactivity of films depending on growth environments and crystallinities will be presented through in vitro cell growth and dissolution studies, i.e., in simulated body fluid and human blood plasma.