Nitinol shape memory alloy has good biomedical application value as an implant, but the corrosion of the alloy will have some adverse effects. At the same time, Ni precipitation will cause cell and tissue allergies, poisoning and other reactions. Therefore, the biosafety of TINI SMAS and its surface modification methods have been studied by many scholars. This paper comprehensively expounds the surface modification technology of TINI SMAS and puts forward the possibility of future development. At present, plasma injection and deposition composite treatment, oxidation treatment, hydroxyapatite and other coating technologies, TiO2 nanotube surface modification methods, etc. can improve the corrosion resistance and biocompatibility of nitinol. In the future, the combination of nanotechnologies and biotechnology may create new materials of scientific and applied value.
Nitinol alloy has excellent shape memory effect, superelasticity (SE), mechanical properties, corrosion resistance and biocompatibility, and is widely used as an implant material in the biomedical field. When NITI rubs against human bone, it has a smaller coefficient of friction and a lower amount of wear. Its strength and fatigue properties are higher than stainless steel, and its elastic modulus is lower than stainless steel. It is close to human bone and is more suitable for bone growth. NITI is also widely used in stomatology, cardiovascular medicine, gynecology and plastic surgery. However, after untreated TINI SMAS are implanted in the human body, the corrosion of the alloy will have some adverse effects, such as poor bone formation process, low osteoininin production activity, and high cell mortality. At the same time, Ni precipitation can cause allergies, poisoning and even cancerous reactions to cells and tissues. Although a thin titanium oxide surface layer (2-20nm) will naturally form on the surface of TINI SMAS, this oxide film is usually unstable, not dense, and prone to peeling and local corrosion. Therefore, suitable surface treatment methods should be used to prevent Ni precipitation. This paper comprehensively expounds the research progress of TINI SMAS surface treatment. At present, the surface treatments used by TINI SMAS mainly include ion implantation, ion implantation and deposition, oxidation treatment, coating, plasma surface alloying, low temperature dealloying, and electrochemical polishing.
Ion implantation will not affect the shape memory effect of nitinol, and an alloy transition layer is formed, which can effectively prevent the modified layer from falling off. At present, the main elements injected into the NITI matrix include 0, C, N, Ta, Cr, Hf, B and P.
TiO2 has good blood compatibility and biological inertness, and can effectively prevent Ni precipitation. Therefore, TiO2 film is an ideal medical protective film.
O ion implantation of NiTi was performed and it was found that the pitting resistance and wear resistance of the alloy were improved. 1×1017cm-2 had the best pitting resistance and wear resistance when injected, while 3×1017cm-2 had reduced pitting resistance when injected. O ion implantation is performed to obtain a TiO2 layer on the surface, and the higher the ion implantation temperature, the thicker the modified layer and the less Ni content. 400℃ is the optimal temperature.
N, c, and O ion implantation were performed, and graded Tin, TIC, and TIO layers were obtained on the surface of the alloy. The wear resistance and cytocompatibility of the alloy were improved, and Ni precipitation was reduced. Among them, the alloy produced the best biological effects after N ion implantation.
N, C, and Ar ion implantation was performed, and it was found that the corrosion resistance improved after N and C injection, while the performance decreased after Ar injection. TiN has good abrasion resistance and biocompatibility, but the generation of residual stress and atomic sputtering will affect the mechanical properties of TiNi and SME.
Ta-PIII was performed on TINI SMAS to obtain the TAOO5/TiO2 layer of the nanostructure and the barren area of Ni, which improved the corrosion resistance and biocompatibility of the alloy.
In addition to the above elements, H20 and Ag can also be injected into TiNi SMAs. H2O-PIII can inject various forms of oxygen (such as H2O+, HO+ and O+) into TINI SMAS, making H2O. After PlII treatment, better electrochemical properties are produced. For the titanium oxide layer prepared on the surface of NITI SMAS by this method, the breakdown voltage is increased from the untreated 250mV to the treated 1000mV, and the passivation current density is reduced by 10 times. It is known that TINIAG ternary alloy Ni precipitates less and has good antibacterial properties. Ag ion implantation is performed on TINI SMAS to obtain a ternary alloy zone on the surface of TINI SMAS. It has the excellent properties of TINIAG ternary alloy without affecting the good shape memory effect of the substrate. Ag ion implantation is a potential method for developing TiNi’s antibacterial properties.
PIIID technology is a novel surface treatment method. This technology uses the atomic mixing zone between the film layer and the substrate to avoid the generation of obvious boundary areas, which can not only improve the binding force of the film base, but also reduce the generation of defects. At present, PIIID technology has been applied to medical materials. The carbide layer and the gradient C/TiNi layer were prepared on the surface of NITI SMAS by the Pill method and the PIIID method, respectively, which improved corrosion resistance. Among them, the PIIID method can promote cell proliferation and better cell compatibility, but both PIIID and Pill increase the surface roughness of the alloy.
The TIC/Ti layer was prepared on the surface of NITI SMAS using PIIID. The surface of the TiC layer is dense and smooth, the hardness and elastic modulus are higher than that of the substrate, and the blood compatibility is also improved. A diamond-like (DLC) film with gradient composition distribution was prepared on the surface of TINI SMAS using PIIID. The precipitation of alloy Ni is very small, the blood compatibility and corrosion resistance are improved, and the SME of the matrix is not affected. The Ni-free (Ti,O)/Ti, (Ti,N)/Ti and (Ti,O, N)/Yi composite layers were prepared using PIIID. The composite layer of nanoscale grains has good wear resistance and is not cytotoxic. The (Ti,O,N)/Ti composite layer has both the biocompatibility of the (Ri,O)/Ti layer and the mechanical properties of the (Ti,N)/Ti layer. Therefore, the (Ti, O,N)/Ti composite layer is a potentially valuable biological coating material.
The TiO2 layer was obtained on the surface of the alloy by atmospheric thermal oxidation method. It was found that 600℃ is the optimal treatment temperature, Ni precipitation is significantly reduced, and endothelial cells can grow on the TiO2 layer. It was found that when the alloy was heated above 600℃ in the atmosphere, a TiO2 layer composed of anatase and rutile was obtained on the surface of the alloy, and the Ni content was almost zero. At this time, TiO2 has good biological activity. However, the appearance of an oxidized mixture of Ni and Ti reduces the corrosion resistance of the alloy. Therefore, TINI SMAS is heated at 400℃ in a 3Pa oxygen partial pressure environment to avoid the production of Ni oxides on the surface of the alloy and obtain high-purity TiO2, which improves the corrosion resistance and wear resistance of the substrate, reduces the coefficient of friction, and has similar structural and electrochemical properties to TiO2 naturally formed on the surface of pure Ti. The oxygen partial pressure was controlled below 7^(-15)%Pa, and the alloy was selectively oxidized with Ti at 600℃, and a high-purity TiO2 layer with a thickness of several nanometers was prepared on the surface of the alloy. After soaking in NACI solution for 168h, the Ni precipitated amount is 0.5%. 19gmol/Cm2, the TiO2 layer effectively prevents Ni precipitation.
The high-temperature oxygen molecular beam oxidation method (HOMB) can prepare an oxide layer on a metal surface. A Ni-free TiO2 layer was prepared on the surface of TINI SMAS by HOMB method. In the entire HOMB process, the process of separation of Ti atoms and diffusion of Ni atoms plays a key role. The HOMB method combined with surface annealing treatment can prepare a thicker Ni-free rutile layer.
As we all know, nanomaterials have excellent overall properties and TiO2 has good biocompatibility. Therefore, the preparation of TiO2 nanotubes on the surface of TINI SMAS has become one of the hot topics in recent years. Anodizing method is used in glycerol electrolyte to obtain Ni on the surface of the alloy.
For doped TiO2 nanotubes, it was found that oxidation voltage and temperature are the main influencing factors for the growth of nanotubes. High voltage accelerates the growth of nanotubes, and high temperature promotes the growth of large areas of nanotubes with openings at both ends. After 35v, 40℃, and 10min anodizing treatment of TINI SMAS, TiO2 nanotubes doped with a small amount of NI2O3 were obtained on the surface. After annealing at 450 and 600℃, it was found that when annealing at 450℃, Ni element was eliminated, corrosion resistance and wetability were improved, and the risk of calcification was reduced. It is suitable as a cardiovascular implant material. And 600℃ annealing time table.
Ti-OH group and rutile are obtained on the surface, which have good corrosion resistance and biological activity, and are suitable for use as plastic materials.
The Ni content on the surface of TINI SMAS after chemical polishing is still as high as 11.5%. 4at%, after subsequent oxidation treatment, a porous TiO2 layer is obtained on the surface of the alloy, with almost no Ni present, which improves its blood compatibility, wetability and anticoagulant properties. Different anode voltages (2～10V) were used to oxidize nano-crystallized and annealed tini smas. It was found that as the voltage increased, the corrosion resistance of nano-crystallized tini smas was better than that of annealed tinismas, and it reached its best at 6V. The reason is that the high-density grain boundary leads to the rapid formation of passivation film. A uniform oxide layer with a thickness of more than 10um was prepared on the surface of TINI SMAS by anodizing. The structure of this layer is tight and there are no cracks, and the grains are fine. The surface is composed of nickel titanate, and the interior is composed of TiO2 and metal Ni, which has good room temperature ductility.
Tini smas was oxidized by Fenton (H2O25%, pH≈3) oxidation method, and a nano-TiO2 layer without Ni was generated in situ on the surface of the alloy, which improved the corrosion resistance of the alloy and hindered Ni precipitation. In addition, after a long period of oxidation in a 30% H2O2 solution, the wetability and blood compatibility of the alloy have been significantly improved.
The coating separates the substrate from the cell tissue, which can effectively inhibit Ni precipitation and improve biocompatibility. However, its binding force with the TiNi matrix is weak, and it is easy to crack or even detach from the matrix under the action of cyclic stress, which limits the application of the coating. Hydroxyapatite (HA) has good biocompatibility and chemical stability. After being implanted in the human body, it will be closely integrated with bone tissue and can maintain normal metabolism in the human body. The preparation of an HA layer on the surface of TINI SMAS can integrate the toughness of metal materials with the wear resistance and biocompatibility of ceramic materials, which has important clinical application value. Soak the acid-base-treated TINI SMAS into the simulated body fluid to obtain an HA layer on the surface. After implanting the rabbit femur, it was found that the HA layer can promote the rapid proliferation of osteoblasts. After implanting 6w, the surface is covered by bone tissue, and after 13w, the HA layer is directly bonded to the bone.
NITI SMAS was soaked in a supersaturated calcium phosphate solution to obtain a calcium phosphate coating (OCP/HAP). OCP/HAP coating promotes cell activation and secretion of cytokines, and its cell adsorption capacity is higher than that of HA-coated TINI SMAS. The reason is the change in the surface morphology of the alloy, indicating that the surface morphology has a great impact on biocompatibility. OCP/HAP coating effectively inhibits Ni precipitation and improves alloy biocompatibility. Although HA has excellent biocompatibility, its mechanical properties are poor and its strength is low, and it cannot be directly used as a substitute material for bone. Carbon nanotubes have good mechanical properties and can be used as enhancers. Recently, it was discovered that carbon nanotubes also have good biocompatibility.
The preparation of hydroxyapatite/carbon nanotube composite materials improved the strength and toughness of HA, and did not produce cytotoxicity. Sol. The method of preparing TiO2 and HA coatings by gel method is simple and easy, and the synthesis temperature is low, avoiding the introduction of impurities.
Sro-SiO2-TiO2 coating was prepared on the surface of the alloy by sol-gel method, which inhibited Ni precipitation, increased the adsorption and proliferation rate of osteoblasts, and the electrochemical properties of the alloy were also significantly improved.
Since the thickness of the surface modified layer prepared by the PIII method on TINI SMAS is very thin (<0.5%), the thickness of the surface modified layer is very thin (<0.5%). 2um), which is easily damaged in some applications, and the thermal oxidation method takes a long time to produce a thick and well-binding oxide layer at lower temperatures, and changes in air humidity will affect the quality of the oxide. Plasma alloying method (PSA) is used to treat the surface of TiNi, and the TiO2 layer is obtained on the surface, which has a good binding force with the substrate, which effectively reduces the content of Ni on the surface and reduces the surface hardness from 2.5% to 2.5%. 5GPa is increased to 11~23gpa, and the wear resistance and corrosion resistance are improved.
The surface treatment of TINI SMAS was carried out by low-temperature dealloying method, and a nanostructured TiO2 layer was obtained on the surface of the alloy, and Ni was completely eliminated at a depth of about 130nm from the surface. After binding hydroxyl groups, the alloy surface has the ability to induce Ca/P deposition, which improves TINI SMAS.
The biocompatibility of the alloy reduces the hemolysis rate, platelet adhesion is reduced, the dynamic coagulation time is prolonged, and the blood compatibility is significantly improved.
Electrolytic polishing and chemical polishing were performed on TINI SMAS, and it was found that after electrolytic polishing, a Ni-free titanium oxide film about 10nm thick was obtained on the surface of the alloy, which effectively inhibited Ni precipitation, and improved wetability, blood compatibility, and antithrombotic properties, while the Ni content on the surface increased after chemical polishing.
Using laser surface alloying method, Mo and ZrO2 were used as alloying materials to prepare an alloying modified layer on the surface of TINI SMAS. There are no microcracks and pores in the modified layer, which effectively prevents Ni precipitation and improves the hardness and abrasion resistance of the material.
A protective film with a gradient composition distribution, compared with a simple surface film, will not affect the performance of the substrate, but also avoid obvious membrane-base interface, high binding force with the substrate, and the gradient composition protective film can effectively prevent Ni precipitation, and it can also provide structural and elemental conditions for the preparation of films with better biocompatible properties. PIIID technology and composite sputtering deposition technology have successfully prepared a gradient component protective film. If effective surface treatment is carried out, an active biological coating can be obtained to meet some special medical applications. The preparation of nanomaterial films on the surface of TINI SMAS will have a profound impact on future medical applications. TiO2 nanotubes with good biocompatibility have been successfully prepared on their surface. Carbon nanotubes are known as the ”king of nanomaterials”, which has excellent performance in all aspects, including high specific strength, excellent chemical and thermodynamic stability, etc., it also has many applications in the field of biomedicine, including biosensors, drug or vaccine carriers, and some unique biological materials with composite nanostructures. Groups of carbon nanotubes have now been prepared on the surface of TINI SMAS. The original carbon nanotubes produce very little cytotoxicity, and the carbon nanotubes are no longer toxic after subsequent chemical treatment and functionalization. At the same time, carbon nanotubes with various functional groups can be prepared, which can improve the binding to human tissue cells.
The three major science and technology of information, life and nano are the mainstream of the development of science and technology in the early 21st century. Combining nanotechnologies and biotechnology on the surface of TiNi SMAs will make it possible to create new materials of great scientific and application value.