Development, application and trend of medical titanium alloy materials

Since the surface of medical titanium and titanium alloys is prone to form an inert passivation film, which affects the combination of implanted devices and soft and hard tissues, surface modification technology has become the key to improving the performance of medical titanium alloys. In recent years, surface modification methods such as physical vapor deposition, plasma spraying, ion implantation, laser cladding, and sol-gel synthesis have been widely studied to improve the surface properties of medical titanium and titanium alloys, such as biocompatibility, wear resistance, and antibacterial properties.

Classification of medical titanium alloys
Titanium alloys can be divided into three categories according to the material microstructure type: α-type, α+β-type and β-type titanium alloys.

Development trend of medical titanium alloys
After investigation, relevant researchers at home and abroad unanimously agreed that the development of medical titanium alloys has gone through three iconic stages.
The first stage is represented by pure titanium and Ti-6Al-4V alloy;
The second stage is represented by new α+β-type alloys represented by Ti-5A1-2.5Fe and Ti-6A1-7Nb;
The third stage is the main development and research of β-titanium alloys with better biocompatibility and lower elastic modulus.
The ideal biomedical titanium alloy material must meet the following conditions: good biocompatibility, low elastic modulus, low density, good corrosion resistance, non-toxicity, high yield strength, long fatigue life, greater plasticity at room temperature, easy to form, easy to cast, etc.
The important alloys that have been widely used in implant materials are Ti-6A1-4V and Ti-6A1-4VELI. It has been reported that V can cause malignant tissue reactions and may have toxic side effects on the human body, while Al can cause osteoporosis and mental disorders. In order to solve this problem, biomaterial scientists are currently committed to exploring and researching new biomedical titanium alloy materials that do not contain V and Al. Before this, it is necessary to figure out what kind of alloy elements are suitable for addition that are both non-toxic and in line with the principle of biocompatibility. Studies have found that β-titanium alloys containing non-toxic elements such as molybdenum, niobium, tantalum, and zirconium contain a higher content of β-stabilizing elements. Compared with α+β-type titanium alloys, they have a lower elastic modulus (E=55~80GPa) and better shear performance and toughness, making them more suitable for implantation in the human body.

1. Application of titanium alloy in facial treatment

When the human face is seriously injured, local tissue repair must be treated with surgical implants. Titanium alloy has good biocompatibility and required strength, making it an ideal material for human facial tissue repair. Skull brackets made of pure titanium mesh have been widely used in jawbone reconstruction surgery and have achieved good clinical results.

2. Application of titanium in the pharmaceutical industry

In the pharmaceutical industry, titanium is mainly used to make containers, reactors, heaters, etc. In the production of pharmaceuticals, equipment often comes into contact with inorganic acids, organic acids and their salts such as hydrochloric acid, nitric acid and sulfuric acid. The equipment is damaged due to long-term corrosion. At the same time, the iron ion pollution caused by steel equipment affects the product quality. The use of titanium equipment can solve these problems. For example, penicillin esterification kettle, saccharification tank, chloramphenicol thin film evaporator, dimethyl sulfate cooler, liquid medicine filter, etc., all have precedents of selecting titanium materials. The quantity and quality of liquid medicine produced by titanium equipment are constantly improving, and the quality is in full compliance with the provisions of the Chinese Pharmacopoeia.

3. Application of titanium in medical devices

In the history of surgical instruments, the first generation of surgical instruments were mostly made of carbon steel, which was eliminated because the performance of carbon steel instruments after electroplating did not meet the requirements of clinical use. The second generation is austenitic, ferritic and martensitic stainless steel surgical instruments, but the chromium in the stainless steel component is toxic, and the detached chromium plating has a certain impact on the human body. Therefore, the third generation - titanium surgical instruments appeared. The light weight and high strength of titanium make it particularly suitable for microsurgery. Titanium has corrosion resistance, good elasticity, and no deformation. Repeated cleaning and disinfection will not affect the surface quality; it is non-magnetic and can eliminate the threat of damage to tiny and sensitive implanted electronic devices. These advantages make titanium surgical instruments more and more widely used. At present, titanium has been used to make surgical blades, hemostatic forceps, scissors, electric bone drills, tweezers, etc. In medical instruments, titanium vascular suture needles, sternal sutures, oxygen filters, one of the cardiac surgical instruments, titanium electrodes in electrocardiographs, titanium incubators in in vitro incubators; probes of medical ultrasonic crushers, automatic controllers for blood transport boxes, and titanium instruments for ophthalmic surgery, etc.

4. Dental Application of Titanium and Titanium Alloys

The metals used in dental surgery started with amalgam and metal crowns in the 1920s. In the 1960s, gold, silver and palladium alloys were mainly used. After the 1970s, stainless steel became the most commonly used material for permanent and removable dental correction devices. In the 1990s, titanium casting technology was promoted and applied. Dental casting using titanium precision casting machines has the characteristics of high dimensional accuracy, no bubbles and shrinkage holes. Among the metal materials used for human hard tissue repair, the elastic modulus of titanium is closest to that of human tissue, which can reduce the mechanical incompatibility between metal implants and bone tissue. The thermal conductivity of titanium is the lowest among all metal materials used for dental restoration. Low thermal conductivity can reduce thermal stimulation to the pulp of teeth with crowns, which is very important for tooth restoration. Titanium inlays, full crowns, etc. have the function of protecting the pulp and avoiding hot and cold stimulation. In terms of material, most of the titanium used in dentistry was pure titanium, but it was not strong enough, difficult to grind, had poor wear resistance, was prone to casting defects and unstable quality. Titanium alloy has high strength, and the most commonly used one is Ti-6Al-4V alloy. However, since metal V is harmful to the human body, Nb is used instead of V, and Ti-6Al-7Nb alloy is successfully developed. It has excellent corrosion resistance and is basically harmless to the human body. It also has other advantages such as strong plasticity and excellent grindability, and has been approved by ASTM standards. At present, titanium can be used to make crowns, crown nails, fixed bridges, porcelain bridges, bonded bridges, denture clasps, bases, connecting devices and reinforcement devices. Almost all metal parts of dentures can be made of titanium. Titanium alloy porcelain teeth can well restore the shape and function of the tooth, and have high strength, beautiful appearance, stable color, smooth surface, wear resistance, and corrosion resistance. It is a permanent restoration suitable for all fixed teeth, especially its good biocompatibility, which is more suitable for people who are sensitive to nickel ions. It has been widely promoted and applied to tooth repair.