In Vitro Cytocompatibility And Corrosion Resistance Of Zinc-doped Hydroxyapatite Coatings On A Titanium Substrate

Metallic implants, such as medical grade titanium and its alloys, are gaining clear advantages for their favourable bioactivity and outstanding mechanical properties. Metallic implants are widely utilised in bone anchoring systems, such as dental and orthopaedic implants, and in osteosynthesis applications. Metallic implants are often coated with osteoconductive biomaterials to ensure their lasting clinical success. Bioactive material coatings that employ hydroxyapatite(HAp) in metallic implants have numerous merits, including improved corrosion resistance of implant surfaces and enhanced osteoconductivity with the sur- rounding tissues. Hence, HAp coatings on metallic implants have been widely investigated in recent years. HAp, with the chemical formula Ca10(PO4)6(OH)2, is hexagonal with a = b=9.432 A?and c = 6.881 A?.However, the low tensile strength, poor mechanical properties, comparatively slow biological interaction rates and high dissolution rate of HAp limit its application in the field of implant materials. Hence, the success rate of HAp-coated implants must be improved. An effective means of promoting osseointegration is to embellish the HAp chemically by doping with trace amounts of beneficial elements that exist in the human body. Bioapatites are generally non-stoichiometric. HAp involves some trace constituents, such as positive ions(Zn2+, Mg2+, Sr2+, Na+and K+) and negative ions(CO32-, SO32- and F-), which influence its physical properties. The apatite structure has excellent flexibility in allowing substitutions. The introduction of trace amounts of ions into the HAp structure improves the quality of biomaterials in a physiological environment.Zinc(Zn) ion is known as one of the most essential trace elements in the human body because Zn is critical to the biochemical processes of cells. Furthermore, bone and teeth are composed of trace quantities of Zn in the HAp structure. Zn significantly contributes to cell growth and proliferation. Zn has a stimulatory function on osteoblast proliferation and stimulates cell proliferation through the synthesis dependency of various cell divisions, promotion-associated enzymes and hor- mones on Zn. Furthermore, ZnHAp coating can improve the corrosion resistance and mechanical properties of both Ti and Ti alloys.ZnHAp coatings that show remarkable bioactivities have reportedly been prepared with the use of a variety of methods. For example, Sun et al. synthesised ZnHAp coatings through electrophoretic deposition. Several reports have shown that surface treatment methods, such as the electrolytic deposition(ED) method, laser cladding and hot spraying, can increase bioactivity while decreasing the corrosion rate of Ti in a simulated body fluid(SBF). ED is an ideal method for the deposition of ion-doped composite coatings. This method has several advantages, such as simplicity of the preparation process, relatively low temperature requirement, capability to coat complex shapes and porous substrates, capability to form a uniform coating and short formation time. Therefore, the ED method can appropriately be applied in the preparation of ZnHAp coating.In this work, a Zn-modified HAp coating is produced on the surface of pure Ti through the ED method, and the microstructure, morphology and composition of the coating are studied. Subsequently, the in vitro bioactivity, cytocompatibility and anticorrosion property of the coated specimens are investigated.