Effect of doping in hydroxyapatite as coating material on biomedical implants by plasma spraying method: A review

Hydroxyapatite (HAp) is still one of the most widely used bioactive coating material to metallic implant in orthopedic fields because of its good biocompatibility, chemical and structural resemblance to natural bone, osteoconductivity, coupled with quicker implant fixation and strong bonding between living bone with implants. Many techniques are used to deposit HAp as coating material on metallic implants among which plasma spray coating stands out as this process is cost effective, reliable, and protects surface of metal from wear and corrosion. Although, HAp is a smart choice as implant coating material, however, its medical application has been restricted because of the unfavorable mechanical properties like brittleness, weak fracture toughness and poor tensile strength. Further, HAp coated implants suffer from longer time period for remodeling, slow osseointegration rate and lack of antimicrobial effects/properties. Different methodologies have been adopted as surface modification techniques to increase mechanical as well as biological properties of HAp. Among those approaches use of dopants in HAp is a very efficient way for modification of properties. Therefore, aim of this review paper is to assemble information related to HAp coating by plasma spray technique on implants and discuss their advantages and limitations. The article also reports how addition of various doping ions into HAp can overcome these limitations by effecting structural, compositional, mechanical properties of HAp. Finally, it reports how the single, binary and multi ion dopants incorporation in the HAp structure can affect the properties which ultimately affect implant functionality when coated by plasma spraying method.

Automated summary

Hydroxyapatite (HAp) is commonly used as a bioactive coating material for metallic implants in orthopedic fields due to its good biocompatibility and structural resemblance to natural bone. However, its mechanical properties can be limiting for medical applications. By using doping ions in HAp, the properties can be modified to improve mechanical and biological characteristics for enhanced implant functionality when coated by plasma spraying method.