Preparation Of Fluorohydroxyapatite Biocoating By Suspension Plasma Spraying

Hydroxyapatite?HA?has a similar chemical structure as that of human bone and teeth.Owing to its excellent biocompatibility,it has been extensively used in many prosthetic applications to improve the direct contact of bone-implants and ultimately minimize the healing time.However,with the increase in the number of traumas and more and more young replacement surgery patients,the requirements for implants are getting higher and higher.The dissolution rate of the HA coating in the body fluid is too fast,and it is easy to cause failure in the implanted body,resulting in failure of bone binding.As well as the coating's poor antibacterial properties,it is easy to cause infection,implant loosening and other issues,it is difficult to meet the actual clinical needs.Fluoridated hydroxyapatite?FHA?,in which F-partially replaces OH-in the HA structure,is considered an alternative material for bone repair because it exhibits low solubility and good biocompatibility.In addition,The HA coatings are fabricated mostly by atmospheric plasma spraying?APS?process as the process is relatively cheaper and has the ability to coat large areas of complex shapes.However,the conventional plasma spray process requires hydroxyapatite powders with good flowability and to prepare such freely flowing powders,tedious agglomeration processes such as spray drying,fusing and crushing are being used.Suspension plasma spraying saves one step in comparison to conventional plasma spraying as fine particles can be directly sprayed onto the plasma in the form of suspension instead of the agglomerated particles.Therefore,we have prepared FHA coating by suspension plasma spraying.This coating has both anti-solubility and antibacterial properties,which is of great significance for the application of implants.Specific conclusions are as follows:1.The FHA powder was synthesized by chemical coprecipitation method,and the FHA water-based suspension satisfying the SPS requirement was prepared.When the dispersant sodium pyrophosphate was added 1.0%,the FHA powder had the longest settling time and the suspension had the highest stability?viscosity 2.38 mPa?s,surface tension 52 N/m?.2.FHA coatings were prepared on the surface of titanium substrate by SPS technique.The effects of different process parameters?spray distance,atomization pressure,spray power?on the microstructure,composition and microstructure of FHA coating were investigated.The XRD result showed that all coatings contained a HA major phase and the decomposition phases??-TCP,?-TCP and TTCP?.FT-IR and XPS confirmed the presence of fluorine in the as-sprayed coatings.3.According to the SEM and mechanical properties analysis,as the spraying distance increases,the coating melting effect becomes worse.When the spraying distance is 40mm,the FHA coating has the highest hardness,the highest density and the best bonding force.The atomization pressure directly affects the droplet size of the suspension and entering the plasma flame and velocity,which in turn affects the melting effect of the coating.When the atomization pressure is 1.25 bar,the FHA coating has the highest hardness,the highest density and the best binding force.In addition,as the spraying power increases,the deposition efficiency and melting effect of the FHA coating are significantly improved.When the spraying power reaches 45kW,the FHA coating has the highest hardness,the highest density and the best bonding force.4.The corrosion behavior was studied in a SBF solution using potentiodynamic polarization test,and the results indicated that the coatings enhanced the corrosion resistance of the Ti substrate.The coatings prepared by the three processes of spraying distance of 40 mm,atomization pressure of 1.25 bar and spraying power of 45 kW have the best protection effect on the substrate,which are 80.86%,90.32%and 81.16%,respectively.5.The chemical stability of the FHA coatings was assessed by evaluating the release of Ca²⁺ions.The results indicated that the substitution of fluorine into the hydroxyapatite?HA?structure had a positive effect on the dissolution resistance of the HA.6.The Antibacterial activity revealed that the antibacterial Activity of the FHA coating was greater than that of the pure HA coatings.cell culture tests showed that the FHA Coating did not exhibit cytotoxicity,and the cell proliferation was comparable with That of the HA coatings.In summary,the process parameters in SPS technology have a crucial impact on the morphology,composition,structure and properties of the coating.The FHA coating has good bioresistance such as solubility resistance and antibacterial properties.The preparation of FHA coating by SPS technology is expected to be widely used in the field of hard tissue replacement and repair.