A review on hydroxyapatite coatings for the biomedical applications: experimental and theoretical perspectives

The production of hydroxyapatite (HAP) composite coatings has continuously been investigated for bone tissue applications during the last few decades due to their significant bioactivity and osteoconductivity. Herein, we highlight the recent experimental and theoretical progresses on HAP coatings, which may bridge the existing gap between theory and practice. The experimental studies mainly deal with electrochemical (EC) and electrophoretic (EP) deposition for the synthesis of nano-HAP in the form of coatings. Additionally, the biocompatible coating method for the fabrication of HAP composite coatings, the plasma spraying (PS) technique, and its mechanism are discussed in this review. Furthermore, the adhesion strength, mechanical, tribological and electrochemical phenomena of HAP composite coatings are critically analyzed. Their ameliorated bactericidal activity is also discussed to recognize the possibility of substituted HAP coatings from a clinical perspective. In addition, computational studies on the HAP system are explored in this report, including the first-principles density functional theory, ab initio modeling and molecular dynamics simulations. Thus, the main significance of this review is to present a collective discussion on the structural features, interfacial mechanics and binding aspects by experimental and theoretical investigations for HAP-based biomaterials, which can provide clear insights for the future research related to orthopedic applications.