Preparation And Properties Of Strontium Titanate Nanotubes Hydroxyapatite Composite Coating On Titanium Metal

Titanium and its alloys are often used as implants to support,replace or enhance damaged biological tissue,including vascular scaffolds,bone and tooth structures due to their physical and chemical properties.The formation of titanium dioxide nanotubes on the surface of titanium significantly increased the specific surface area of titanium and increased the cell adhesion sites.When titanium metal is used as an implant into the physiological,it is difficult to improve bioactivity of implant because tanium oxide layer on the surface titanium are biologically innert.Strontium-a trace element but necessary element in bone has been reported to promotes the bone formation by osteoblasts and reduces bone resorption.When strontium doped into TiO₂ nanotubes,the osteogenic effect can be produced without changing the tubular structure of the oxide layer,which is conducive to cell adhesion.Hydroxyapatite has also been widely used in the field of bone repair materials in recent years,because its chemical composition,structural properties and biological activity are similar with human bones.So it which promote the attachment and differentiation of osteoblasts and improve the osteogenic activity of implant materials.In this paper,a composite hydroxyapatite coating was deposited on the surface of strontium titanate nanotubes by electrochemical method to improve the osteogenic activity of the implant material.In order to better inhibit the attachment of microorganisms,silver and europium elements were doped into the coating.A series of studies on the properties of the final composite coating were carried out.The main contents are as follows:Firstly,TiO₂ nanotubes with uniform diameter were prepared on the surface of titanium by anodic oxidation method.The selected anodic oxidation voltage is 60 V,the reaction time is 120 min,the selected electrolytic liquid system is NH₄F,water glycol solution The average diameter of the TiO₂-NT samples was approximately 130nm.The amorphous TiO₂ prepared by anodic oxidation can be transformed into anatase with more stable properties by heat treatment at 450?.Then,the strontium titanate coating was prepared in strontium hydroxide solution by hydrothermal method at 200?.The doping of strontium element made the nanotube wall thickened and diameter slightly decreased,while the tubular structure did not change.The prepared strontium titanate coating can release strontium ions with osteogenic activity for a period of time.Silver doped hydroxyapatite coating(Ag-HA)was prepared on the surface of strontium titanate nanotubes by electrochemical method.The results show that the morphology of the prepared coating is uniform and the crystallinity is the best when the current density is 2 mA/cm².The coating surface is porous in which silver ions are evenly distributed.The bonding strength of the coating reached 16.49 MPa.The corrosion resistance test and immersion test in SBF proved that the corrosion potential and biological activity of the composite coating were significantly improved compared with pure Ti.Biological evaluation showed that the composite is a antibacterial and it also had no obvious cytotoxicity.Silver ions and strontium ions in the coating can be released slowly over a period of time.The rare earth element Europium is also doped into the composite coating by the same electrochemical method.According to the different Eu doping ratio,the Eu-HA material is prepared.When the Eu³⁺/(Eu³⁺+Ca²⁺)value is 1%,the coating has the best crystallinity and the highest binding strength.However,when the ratio is increased to15%,the hydroxyapatite coating can't be prepared in STN by electrochemical deposition experiments.The performance study confirmed that the hydrophilic,corrosion resistance,biological activity and antibacterial properties of the composite coating were greatly improved compared with Ti.In addition,strontium and europium ions can be released slowly in PBS solution for a period of time.