【Summary】Titanium and titanium alloys are gaining more and more attention in the field of biomedical metal materials due to their high specific strength, good biocompatibility, elastic modulus close to natural bone and good corrosion resistance. This paper reviews the development of biomedical titanium alloy materials and products and their application status in biomedical engineering, and points out the future development direction and application goals of biomedical titanium alloy materials and products.

1 Introduction
        Biomedical metal materials are metals or alloys used to diagnose, treat, repair or replace damaged tissues, organs or functions of living organisms. They are mainly used for the repair and replacement of hard tissues such as bones and teeth, cardiovascular and Soft tissue repair and the manufacture of artificial organs. With the vigorous development and major breakthroughs in biotechnology, the biomedical metal materials and their products industry will develop into a pillar industry of the world economy in this century. Pure titanium and its alloys have been used more and more widely in clinical practice due to their similar elastic modulus to bone, good biocompatibility and excellent corrosion resistance in biological environments. Biomedical titanium alloy materials have become the main raw materials for the production of surgical implants and orthopedic devices worldwide.

2 The purpose of research on biomedical titanium alloy

         Metal materials are the first biomedical materials used in clinical medicine. The metal materials currently used for surgical implants and orthopedic instruments mainly include three series of stainless steel, cobalt-based alloys and titanium alloys, which account for 40% of the total biomaterials market share. %about. Among them, titanium alloy has been widely used in the repair, orthopedics and replacement of defects, trauma and diseases in human hard tissues (including all bones and teeth in the human trunk). Since the middle of the 20th century, titanium-based medical metal materials have begun to show in the surgical implantation of human hard tissues and the interventional treatment of human soft tissues (including cardiovascular and cerebrovascular, peripheral blood vessels and non-vascular such as liver, biliary tract, urethra, etc.). Unique and miraculous curative effect, and the advent of typical representative medical device products such as titanium alloy artificial joints, dental implants, endovascular stents and heart valves, has epoch-making significance and revolutionary contribution to the development of medicine, making clinical Treatment from the simple "repair, orthopedic" treatment of the primary to the higher-level "alternative" treatment of tissues and organs, greatly improving and improving people's quality of life, overcoming the previous major diseases can only rely solely on drug treatment insufficient.

         The development of titanium and its alloys can be divided into three eras. The first era is represented by pure titanium and Ti-6Al_4V. The second era is a new type of d+ represented by Ti-5M-25Fe and Ti-6AI-7Nb. Type 13 alloy, the third era is an era of development and development of better biocompatibility and lower modulus of elasticity titanium alloy, which is the most extensive research on p-type titanium alloy. The titanium alloy originally used in clinical practice is mainly represented by pure titanium and Ti-6A1-4V. Pure titanium has good corrosion resistance in physiological environment, but its strength is low, its wear resistance is poor, which limits its application in carrying large parts. It is mainly used for oral restoration and bearing a small part of bone. Replaced, but there is no strength issue yet. In contrast, Ti-6A1-4V has high strength and good processing properties. This alloy was originally designed for aerospace applications and was widely used as a surgical repair material in the late 1970s. Such as hip joints, knee joints, etc. At the same time, Ti-3AI-2.5V is also clinically used as a replacement material for femur and tibia.

3 Development status of biomedical metal materials industry at home and abroad

        3.1 Development status of domestic biomedical titanium alloy

        The application and development of biomedical titanium alloy materials in China started late, the overall level is not high, the tracking research is more, the source innovation is less, the products with high technical content mainly rely on imports, the biomedical metal materials and equipment industry foundation is weak, and the product technology structure And the level is still basically in its infancy. As a new industry, the medical titanium alloy industry has great development prospects. It has maintained a high growth rate for more than a decade, and it contains enormous economic and social benefits. The innovation system of investment in China. For the enterprise itself, we must also recognize that today's investment is the cultivation and guarantee of the future corporate competitiveness, increase investment in scientific and technological innovation, and establish a technological innovation system based on enterprises. In combination with China's national conditions and the development trend of biomaterials, Professor Yu Yaoting, vice chairman of China Biomaterials Association, proposed that China should carry out key research in the following five aspects: one is the study of the design and construction principles of biological structure and biological function, and the other is surface/ Interface process - the interaction mechanism between the material and the body, the third is the biological guiding and the controlled release mechanism of biologically active substances, the fourth is the research mechanism of biodegradation / absorption, and the fifth is the preparation method and quality control of materials. System research. The research focus of these five aspects is equally applicable to medical titanium alloys.

         China's research and application of medical titanium alloy materials began in the 1970s. After the preliminary research on the imitation of Ti6Al4V, Ti6Al7Nb and Ti5Al2.5Fe medical titanium alloys, the Northwest Institute of Nonferrous Metals developed the first in China for the first time in 1999. The nearly α-type new medical titanium alloy TAMZ (Ti2.5Al2.5Mo2.5Zr) with independent intellectual property rights has the same comprehensive performance as Ti6Al7Nb. In 2005, the Northwest Institute of Nonferrous Metals developed two new high-strength low-modulus near-beta medical TiZrMoNb (TLE) and TiZrSnMoNb (TLM). The Institute of Metals of the Chinese Academy of Sciences has also developed a new low modulus near-beta titanium alloy Ti24Nb4Zr7.6Sn (Ti2448). In addition, Beijing Nonferrous Metals Institute, Harbin Institute of Technology, Northeastern University, Tianjin University and other units are also developing new beta-type titanium alloy applications and related basic research.

         3.2 Development Status of Foreign Biomedical Titanium Alloys

         In the early days, the development of low-modulus die-shaped titanium alloys was mainly concentrated in the United States, and in recent years Japan's research in this field has been very active. Non-toxic alloying elements should be used in the manufacture of biomedical titanium alloys. The risk of metal allergy should also be considered. In dental medicine, Co, Cr and Ni have been pointed out to be closely related to metal allergy. In addition, since Al is a biologically unfriendly element, it is not required to contain or contain only a very small amount in the development of new alloys. A large number of experiments have shown that elements such as Nb, Ta, Zr and sn have good biocompatibility and less toxicity and are considered to be safe biomedical alloying elements. At present, the internationally developed non-toxic, non-allergenic alloying elemental titanium alloys include: Til3Nbl3Zr, Til2M06Z, Til2M05Zr5Sn, Til5Mo, Til6Nbl0Nb0.2Si, Til5M05Zr3Al, Ti30Ta, Ti45Ti35Nb7Zr5Ta, Ti29Nb 13Ta4.6Zr(TNTZ), Ti8 and TiSFe8Ta4Zr, etc., they are mainly used for artificial hip joints, artificial tooth roots, bone plates and screws, implant rods (main components for spinal internal fixation devices) and other biological implants. These titanium alloys have a low modulus of elasticity, which facilitates stress buffering and uniform transmission between the implant and the bone.

         In the past five years, Japan has focused its research on such things as Ti. 10Cr. AI, Ti. Mn, Ti. Fe. Nb. Zr, Ti. Sn-Cr, Ti-Cr. On the biomedical titanium alloy, they also developed 7Fi. 30Zr gold for detachable implants. At the same time, they also developed Ti-30Zr. (Cr, Mo) and Ti. 12CrE9] alloys, which resist deformation during deformation during orthopedic surgery and maintain a low modulus of elasticity.

         Russia has developed a new medical titanium alloy, Ti51-Zrl8Nb (at%), which has a low modulus of elasticity (47 GPa) and a high reversible shape (2.83%). The design principle of this alloy is: when binary Ti. When yttrium is added to the zr alloy, the atomic radius of titanium and zirconium causes a special change in the electronic structure, thereby forming a mechanically unstable β phase, which can cause α-β phase transition during deformation. .

         The United States has also developed a variety of low modulus beta titanium alloys, of which the preferred alloy for replacing the hip joint is Ti. 35Nb. 7Zr. 5Ta (Ti-Osteum) and Ti-1 3Mo. 7Zr. 3Fe(TMZF), which has a lower modulus of elasticity and a low modulus of elasticity close to the skeletal modulus of the human body, reducing the occurrence of "stress shielding", reducing the loss of bone density and reducing the ultimate failure of the implant. The odds are very important. These two new alloys have been gradually recognized and accepted internationally in the past four years.

         The lowest modulus of elasticity that has been reported so far in titanium alloys is 40 GPa, which is obtained on Ti-Nb-Sn alloys. It is very difficult to further reduce the modulus of elasticity to below 40 GPa. The deformation behavior of some die-shaped titanium alloys has severe anisotropy. Since the elastic modulus depends on the grain orientation, the β-type titanium alloy single crystal material obtained along a certain crystal orientation growth may reach less than 40 GPa. s level. It has been reported that a single crystal of a certain crystal orientation can obtain an elastic modulus of less than 40 GPa. It can be seen that single crystal titanium alloy is also expected to be used in the biomedical field in the future.

4 Introduction to research results of biomedical titanium alloy

         In order to replace the commonly used Ti-6A1—4V alloy, a variety of new acoustic titanium alloys with non-toxic and non-sensitive elements, low elastic modulus and high mechanical properties have been developed. The porous technology is used to adjust the porosity to make the material elastic. The modulus is basically the same as that of human bones. The method of infiltrating the polymer into porous titanium compensates for the decrease of the strength of porous titanium and makes the material have better biocompatibility. In order to meet the needs of orthopedics, porous TiNi is developed. The elastic shape memory alloy overcomes the disadvantages of weak bonding force between the bone and the implant and mismatch of the elastic modulus. In addition, a variety of β-type superelastic shape memory titanium alloys containing no toxic and allergic elements have been developed, which can be used safely in the medical field instead of TiNi alloys: various surface modification techniques for titanium have been developed and modified. The deposition and surface hardening of the layer improves the biocompatibility and abrasion resistance of the implant.

         In order to further improve the biocompatibility of titanium implants, various surface modification techniques have been developed in recent years in the world. The hydroxyapatite layer, the titanium oxide layer and the perovskite layer of different morphologies can be deposited on the surface of the titanium alloy by electrochemical treatment including micro-arc oxidation; the hydroxyapatite-free and chemically obtained The surface-modified layer of tricalcium phosphate accelerates bone formation; it also controls the absorption of proteins and the adhesion of cells, platelets and bacteria by immobilizing biological functional molecules such as polyethylene glycol on metal surfaces. Furthermore, in the case of immobilization of biomolecules such as collagen and polypeptide, bone formation and adhesion of soft tissues are improved. In recent years, Japan has done a lot of research on the surface bioactivation modification of titanium alloys. They used alkali treatment, electrodeposition and metal organic chemical vapor deposition (MOCVD) to form a hydroxyapatite modified layer on the metal surface to improve metals such as polymethyl methacrylate (PMMA) E3 31, polylactic acid ( PLLA) 1343 and other medical polymers and blood compatible with biopolymers such as polyethylene glycol (PEG) r351. On the other hand, in order to improve the wear resistance of titanium alloys, surface hardening is an effective method, including surface oxidation, nitridation, electroplating, and physical chemical vapor deposition (PVD/CVD) coating, thermal spray surface treatment technology. Research and development. Among these technologies, oxidation and gas nitriding are advantageous because they require only a simple process operation. In recent years, Japan has conducted extensive research on Ti02 as a photocatalyst and its use in surface modification to enhance the bioconductivity of titanium and its alloys.