Stainless steel, cobalt-based alloy and titanium-based alloy are three kinds of medical metal materials commonly used in clinic, which have the characteristics of high strength, good toughness and high stability. With the progress of preparation process and technology, new biological metal materials are emerging, such as powder metallurgy alloy, high entropy alloy, amorphous alloy, low modulus titanium alloy and so on.
(1) Mechanical properties. Biomedical metal materials should generally have sufficient strength and toughness, appropriate elasticity and hardness, good fatigue and creep resistance, as well as necessary wear resistance and self-lubricity.
(2) corrosion resistance.
(3) biocompatibility. Specifically reflected in: non-toxic, non-stimulating, non-carcinogenic, non-mutagenic effect on the human body; no rejection in the human body; firm combination with surrounding bones and other tissues, preferably to form chemical bonding and biological activity; no hemolysis, clotting reaction, that is, antithrombotic.
1. Titanium alloy.
Biomedical titanium alloy is a kind of functional and structural materials used in biomedical engineering, which is often used in the production and manufacture of surgical implants and orthopaedic instruments. Titanium alloy medical devices, such as artificial joints, dental implants and vascular stents, are used for clinical diagnosis, treatment, repair, replacement of human tissues or organs, or improve the function of human tissues or organs, which can not be replaced by drugs.
Pure titanium has the advantages of non-toxic, light weight, high strength and good biocompatibility. In the 1950s, the United States and Britain began to use pure titanium in organisms. After the 1960s, titanium alloy has been widely used in clinic as a human implant material. From the initial Ti-6Al-4V to the subsequent Ti-5Al-2.5Fe and Ti-6Al-7Nb alloys and the new β titanium alloy developed in recent years, the research of titanium alloy in human implant materials has made rapid progress.
two。. Cobalt-based alloy.
Cobalt-based alloy usually refers to Co-Cr alloy, which has two basic grades: Co-Cr-Mo alloy and Co-Ni-Cr-Mo alloy. The microstructure of Co-Cr-Mo alloy is cobalt-based austenite structure, which can be forged or cast, but it is very difficult to fabricate. Its mechanical properties and corrosion resistance are better than stainless steel, so it is an excellent biomedical metal material at this stage. Forged cobalt-based alloy is a new material, which is used to manufacture the trunk of joint replacement prosthesis, such as knee joint and hip joint replacement prosthesis.
The American Society for Materials experiment has recommended four cobalt-based alloys that can be used in surgical implants: forged Co-Cr-Mo alloy (F76), forged Co-Cr-W-Ni alloy (F90), forged Co-Ni-Cr-Mo alloy (F562), forged CoNi-Cr-Mo-W-Fe alloy (F563), of which F76 and F562 have been widely used in implant manufacturing.
3. Stainless steel.
Medical stainless steel is widely used in stomatology, fracture internal fixation instruments, human joints and other fields because of its low cost, good processability, mechanical properties and so on. 302 stainless steel is the earliest medical metal material with good corrosion resistance and high strength. Some researchers added molybdenum to stainless steel to make 316 stainless steel, which effectively improved the corrosion resistance of medical stainless steel. In the 1950s, researchers developed a new 316L stainless steel, which reduced the maximum carbon content in stainless steel to 0.03%, which further improved the corrosion resistance of the material. Since then, medical stainless steel has become internationally recognized as the preferred material for surgical implants.
In order to avoid the toxicity of nickel, researchers have developed high-nitrogen nickel-free stainless steel. In recent years, low-nickel and nickel-free medical stainless steel has been gradually developed and applied. The material and Materials Research Institute of Japan (Tsukuba) has developed a simple production method of nickel-free hard stainless steel, which solves the problem that nickel-free stainless steel is difficult to process and the manufacturing cost is too high, and the production cost is low. It is expected to be widely used in medical field.
4. Aluminum alloy.
Aluminum and its alloy materials have good properties, plasticity and compatibility, so they have been widely used as implant materials as early as the 1940s. At present, parts that can bear high loads are also made of aluminum and its alloys. Aluminum has high corrosion resistance, except in the mixture of hydrofluoric acid, caustic alkali, hot concentrated sulfuric acid, hydrochloric acid and nitric acid, its reagents can not corrode aluminum, and body fluids do not affect the alternating fatigue strength of aluminum. good biocompatibility makes aluminum implant materials do not stimulate the human body. In addition, compared with stainless steel, aluminum has higher resistance to notch crack growth.
5. Magnesium alloy.
As a biodegradable biomaterial, porous magnesium alloy can provide three-dimensional space for cell growth, which is beneficial to the exchange and transport of nutrients and metabolites. Magnesium itself has biological activity and can induce cell differentiation and angiogenesis. In the process of material degradation and absorption, the implanted cells will continue to proliferate and grow, and it is expected to form new corresponding tissues and organs with specific functions and forms, in order to achieve the purpose of wound repair and reconstruction. Biomedical degradable magnesium alloy materials are expected to be widely used in clinical hard tissue repair or replacement because of their complete degradability and excellent biocompatibility. Biodegradable magnesium alloy vascular stent is the biggest research progress of magnesium alloy as biodegradable biomedical metal materials.
Biomedical magnesium alloys have attracted wide attention because of their good biocompatibility, mechanical compatibility and degradability, but the rapid corrosion rate limits their practical application.
The future research directions of degradable magnesium alloy materials are as follows: (1) improving the corrosion resistance of magnesium alloy by alloying, cold working, heat treatment and surface treatment; (2) the effect of alloy elements on the biocompatibility of materials; (3) the analysis of the changes of mechanical properties of materials during corrosion; (4) composition analysis and biosafety evaluation of corrosion products of degradable magnesium alloy materials.