Nickel Electrodeposition Of Hydroxyapatite On Titanium Alloy Surface And The Effect Of Edta - 2 Na

Nitinol is an alloy formed with the same number of titanium and nickel atoms.Nitinol has the characteristics of shape memory and superelasticity, and therefore can beused in clinical as corrective brace for scoliosis and teeth orthopaedic silk vascularstents, medical wire. Nitinol is a toxic metal material, and its biocompatibility is poor.In order to use the excellent mechanical properties of Nitinol in medicine, we have tobiologically activate the material.In recent years, hydroxyapatite has aroused widespread concerns. It is inorganicingredients of the skeleton of vertebrate. It has excellent biological activity, and can bechemically synthesized in vitro, which makes mass production possible. The poormechanical property of hydroxyapatite makes it not suitable for load-bearing.In view of the strengths and weaknesses of both nitinol and hydroxyapatite, it wasenvisaged that the two materials may be synthesized. Synthesis can make full use of thebioactivity of hydroxyapatite and mechanical properties of the nitinol. There are manykinds of synthetic methods, such as plasma spraying method, the sol-gel method, thebionic method, and electrochemical deposition. Due to the mild reaction conditions,short cycle and the ease to control the condition, electrochemical deposition hasattracted people’s attention. This method was used in this paper.The electrochemical deposition conditions, such as the current density, depositiontime and the complexing agent (EDTA-2Na), have been explored in this paper. Theanode corrosion, hydrogen peroxide treatment and heat treatment of alkali (NaOH) havebeen used for improving biological activity of the material. The experimental results areas follows.Anode corrosion can form a porous morphology and expand the surface area of thematerial, which is conducive to the mineralization of hydroxyapatite. An oxide layerwas formed after hydrogen peroxide treatment. There was a transition layer between thenickel-titanium bottom and hydroxyapatite coating, which can reduce the gap of thecoefficient of thermal expansion between the nickel-titanium bottom and hydroxyapatitecoating. Na2TiO3on the surface was formed after alkali heat treatment which can induce hydroxyapatite nucleation and growth. It would be optimised to set the current densityat1mA/cm2, then the single hydroxyapatite is strong and number of the hydroxyapatiteis huge enough to cover the nickel-titanium base. One hour of electrochemicaldeposition is appropriate, then the single hydroxyapatite is strong and the coverage ofthe basement is full. There occurred crystallization when electrochemical depositiontime was more than1hour.The optimised amount of substance concentration of EDTA-2Na in theelectrochemical deposition solution is1.5~2.5×10-4mol/L, then the hydroxyapatitenumber is large enough to cover the basement fully. The space between differenthydroxyapatites is large. The ends of different hydroxyapatites were coiled together.This loose structure is conducive to the attachment of cell pseudopodia.Addition of EDTA-2Na not only makes the single hydroxyapatite slender and thecoating denser, but also makes the peak of hydroxyl group of hydroxyapatite sharper,and effectively inhibits the growth of the carbonate. Adding of EDTA-2Na makes thehydroxyapatite grow slowly and uniformly, and has a stronger inhibitory effect on thenickel than titanium when other experimental conditions are similar.Mimic physiological fluid immersion tests show that there are sporadicmineralizations occuring on the nitinol surface chemically polished only, and themineralization number was significantly increased when the surface of nitinol wastreated by hydrogen peroxide. Introduction of EDTA-2Na makes mineralization smoothand uniform. Energy spectrum (EDS) showed that adding of EDTA-2Na make thespeed of mineralization slow down. Osteoblasts can adhere to the surface ofhydroxyapatite coatings containing EDTA-2Na, that means the hydroxyapatite coatingwith EDTA-2Na has good biological activity.The tensile test showed that adding of EDTA-2Na doubled the bonding strength ofnickel-titanium basement and hydroxyapatite coating.Corrosion experiments showed that adding of EDTA-2Na can improve thecorrosion resistance of the coating.XRD results showed that adding of EDTA-2Na can promote hydroxyapatite ‘spreferential growth along the c axis.