Electrochemical Synthesis Of Porous Hydroxyapatite And Formation Mechanism

Porous hydroxyapatite coatings were prepared on porous soft polyurethane foam plastics base using pretreatment(unoil,sensitization,activation,peptization) and electrochemical deposition method. The purpose of experiment is to improve the bonding strength between the coating and the base and to carry on previous technical process research and theory analysis for its application.The experiment of pretreatment shows that porous soft polyurethane foam can be washed clearly by both organic and chemical unoil.The result of activation is perfect even if the cheaper silver nitrate instead of expensive palladium chloride is used as active agent in the experiment,the surface of porous soft polyurethane foam can also be plated a thin metallic silver atoms layer. Silver atoms which were covered by gel layer in the process of activation appear in the surface of soft polyurethane foam as a catalyst by peptization. After pretreatment,there is a layer of the metallic silver atoms as reductant on the surface of porous soft polyurethane foam.The skeleton of foam is a hollow,open-tubular structure after pretreatment by SEM..Hydroxyapatite coatings were plated on porous soft polyurethane foam plastics base using electrochemical deposition method after pretreatment. The effect of influencing factors such as the time of electrodeposition,voltage,concentration,temperature on the microstructure,the surface morphology,the quality of deposition of the coatings were studied.Different testing instruments including XRD,FT-IR,SEM were employed to characterize the coatings. The mechanism of electrochemical deposition for the HA coating was discussed based on the experimental results.The experimental results show that the hydroxyapatite coatings are porous by electrochemical deposition method , porous hydroxyapatite coatings gradually become more and more by extending time, raising temperature , increasing concentration ,improving voltage,until almost completely cover the surface of porous polyurethane foam,these sediments gather each other and their distribution is asymmetric,but this structure increases specific surface area of the foam. By XRD figure of porous hydroxyapatite coatings,these sediments are pure hydroxyapatite phase by electrochemical deposition. From FT-IR of porous hydroxyapatite coatings,3571cm^-1 for OH- telescopic vibrating peak and 632cm^-1 for OH- swinging vibrating peak,963cm^-1,602cm^-1,566cm^-1,1036cm^-1 for PO₄^3-.In addition,a peak of 1648cm ^-1 and wide spectrum band of 3000cm ^-1 3600cm^-1 area are feature of absorbing water.But 872cm^-1 for HPO₄^2-,the result shows the composition of coatings is calcium deficient hydroxyapatite[Ca_10-x(HPO₄)_x(PO₄)_6-x(OH)_2-x].Porous hydroxyapatite coatings were immersed into simulated body fluid,the biocompatibility and bioactivity of the coatings were evaluated by the experiment of SBF immersion. The results show that the surface of coatings are covered by carbonate apatite layer after being immersed in SBF for 9 days,they grow and gather each other,apatite particle size increases obviously,some small apatite particles constitute big apatite particles. In addition,PH value of SBF falls with the extension of soaking time.