Study Of Bioactive Coatings On The Surface Of Titanium And Nitinol By Micro-arc Oxidation

Titanium and Nitinol(NiTi) have been widely used as orthopedic implants because of their excellent mechanical properties and biocompatibility,NiTi also applies to vascular stent materials.However,the surface of titanium alloy can not be directly related to human bone tissue to form chemical bonding,and NiTi have issues of Ni²⁺ ion toxicity,thrombosis,and so on.The coating of hydroxyapatite(HA) on the implant surface has been suggested as the most effective way to provide biocompatibility and Osseo conductivity.But HA has shortcomings of brittleness,weak combination and easy off.Micro-arc oxidation(MAO) is a method to prepare metallic oxide-based micro porous coating with good corrosion resistance,high bond strength.In this paper,In order to improve the biocompatibility of titanium and nickel-titanium alloy,TiO₂ porous coatings with HA(or Ca,P component) were prepared on medical titanium and NiTi alloy by Micro-arc oxidation.The electrolyte solution of calcium acetate((CH₃COO)₂Ca·H₂O) with sodium dihydrogen phosphate(NaH₂PO₄·2H₂O) was used to micro-arc oxidation.By controlling the electrolyte concentration,electrical parameters,HA/TiO₂ biocompatible porous coatings were prepared on the surface of titanium;and heat treatment,ion plating combination with micro-arc oxidation were used to prepare micro porous biological activity coatings on the surface of NiTi.Structure and Properties of coatings were characterized using SEM,EPMA, XRD,Raman spectroscopy techniques,as well as surface energy testing,electrochemical corrosion testing.Mineralization ability of coatings was studied by in vitro Mineralization test and blood compatibility of coatings was characterized by platelet adhesion test.The impact of the electrolyte concentration and electrical parameters to the structure of MAO coating and biological properties of different electrolyte concentrations were studied. The results show that pore size and thickness of coating increased with the augment of electrolyte concentration,and the augment of pore size could raise the surface energy.When the mole ratio of calcium to phosphate was controlled at 1.67 respectively,TiO₂ with HA formed in the surface of titanium.Coating has good corrosion resistance and mineralization ability in the Tris' simulation body fluid.Platelets on the surface of the sample are neither distorted nor congregated,which shows superior blood compatibility.And the increasing of electrical parameters will make the pore size and thickness of coating increase,the anatase phase reduce,the rutile phase raise,as well as the increase of HA,Ca₃(PO₄)₂ components.The preparation of porous coatings on the surface of NiTi by heat treatment,ion plating combination with micro-arc oxidation was studied.The results show that uniform micro porous coating with Ca,P component formed on the surface of NiTi wires by MAO after heat treatment at 500℃.And the ratio of Ti/Ni and Ca,P content in coatings increased with the prolonged oxidation time.When voltage is 550V,duty cycle is 15%,well-distributed micro porous coatings were acquired by MAO treated for 20 seconds.The average pore size of micro porous on surface was about 1μm,and the platelet adhesion test showed superior blood compatibility of the coatings.A porous TiO₂-based coating formed on the surface of NiTi by micro-arc oxidation after ion plating,The Ni content of coating remained less than 1%,large particles in the surface significantly reduced with the increasing of duty cycle and extension of time.When voltage is 520V,duty cycle is 15%,uniform micro porous coating was formed after MAO treated for 40 seconds and pore size of surface was about 1～2μm,and the platelet adhesion test showed superior blood compatibility of the coatings.