Preparation And Biological Properties Of Titania/polydopamine Coatings On NiTi Alloy

Medical metal materials have an important position in medical field because of their excellent performances.In titanium alloy material systems,NiTi alloy with good super-elasticity and shape memory effect has been applied in the fields of dentistry,orthopedics,and cardiovascular surgery.The contents of Ti and Ni in most Medical NiTi alloy components are both at 50.5⁵1.5at.%.However,Ni ions are potentially toxic,long-term placed in the body,it may cause corrosion to elute Ni ions,and incur diseases that are toxic to the human body.Moreover,the NiTi alloy has poor biological activity and it is difficult to combine with human bones after implantation in the human body,resulting in slow healing of the surgery.Therefore,this article uses micro-arc oxidation technology to improve its wear resistance and corrosion resistance the surface modification of NiTi alloy by modifying the surface of NiTi alloy,because dopamine has good biological properties and it can combine with the compound polydopamine to improve its biocompatibility.The surface morphology and composition of the obtained film were analyzed by SEM and XRD tests.The ability of the membrane layer to induce deposition of hydroxyapatite was studied by using simulated body fluid soaking and the bioactivity of the membrane layer was analyzed.The micro-arc oxidation uses concentrated phosphoric acid as the electrolyte,and the power supply adopts the constant current mode of the AC power supply to change the current density,processing time and frequency respectively.The NiTi alloy was processed under different conditions to obtain the best preparation parameters.The obtained TiO₂ film surface had a typical porous morphology,and the film thickness is 3-7 micrometers.The film layer can effectively reduce the Ni ion content on the surface.The material inside the film was amorphous and can be crystallized into anatase TiO₂ after hydrothermal treatment.The roughness gradually increases with the treatment time,and decreases with the increase of current density and frequency.The bonding strength is not less than 45 MPa,and the bonding strength with the substrate is high and the binding effect is good.The results show that the best surface morphology,thickest and densest layer.Best corrosion resistance are obtained at the processing time of 120 s,the current density of 0.2A/cm2 and the frequency of 50 Hz.Simulated body fluid soaking of the membrane layer reveal that the surface was generally capable of inducing deposition and the biological activity was slightly poor.The TiO₂ film layer obtained by the micro-arc oxidation method wascomposited with trihydroxy aminomethane and dopamine hydrochloride to obtain a TiO₂ /polydopamine composite film layer.On the surface of the composite film,bright particles were distributed and the film was brown.The existence of polydopamine coating measured by EDS and infrared spectroscopy were proved.After the compound polydopamine,the corrosion potential of the film was significantly shifted and the corrosion performance became better.Simulated body fluid soaking revealed that as the soaking time prolonged,the calcium-phosphorous-based deposits induced on the surface of the film layer increased,the sedimentary layer became thicker,and the deposition effect was better.Combined with XRD pattern analysis,it was found that the induced calcium-phosphorus-based sediment was a calcium-deficient apatite.The results showed that the TiO₂ coating combined with polydopamine composite films after hydrothermally treated had good corrosion resistance,and the ability to induce apatite deposition was the strongest,furthermore,it had excellent biological activity.