The adaptability of titanium alloy materials to the human body and the types of medical titanium materials
In the medical industry, when metal materials are used, they must be absolutely harmless to the human body. When metal corrodes, it can dissolve metal ions and affect the cell tissue of the organism (human body). Therefore, it is necessary to choose metal materials that are not easy to corrode and have high corrosion resistance. Titanium is a kind of high corrosion resistance material. Medical metal materials range from stainless steel series to cobalt-based and titanium-based alloy series, and the proportion of titanium and titanium alloys is increasing. The amount of titanium used in the medical industry around the world is about 1000t a year.
1. The adaptability of titanium to the human body (compatibility of titanium to organisms)
In order to observe the response of metal ions to human adaptability, in the laboratory, mouse lung fibroblasts (V79 cells) and mouse (20 days postnatal mice) fibroblast tissues (I929 cells) were used in Chinese medical experiments. ), etc., using cells that are sensitive to metal ions to carry out cell adaptability evaluation methods. ) The reactions are divided into 3 groups as shown in Figure 1.
Vanadium (V), nickel (Ni), copper (Cu), etc. are definitely toxic. When the content of the above elements is in parts per million (×10-6), the cells will die in a short time. Taking vanadium (V) and nickel (N) as examples, the results of experiments conducted on V79 cells are shown in Figure 2. The results of the immersion test for a week show that if the nickel is about 10×10-6 (translator's note pm = parts per million), all cells die. In contrast, vanadium (V) is two digits less than 0.6. ×10-6 is the cell death. Secondly, when the hard tissues (bones) and soft tissues (muscles) of small animals such as rats and rabbits are buried in metal sheets for testing, it must be that these highly toxic metals are in contact with hard tissues (bones) and soft tissues (muscles). Partially caused necrosis.
The relationship between the formation energy of a-V79 cell population and the concentration of nickel (Ni) ions;
The relationship between b-V79 cell population formation energy and vanadium (V) ion concentration
The other group represents trauma. In the state of implantation, a biological reaction is formed on the fibrous tissue at the contact site, which is expressed by iron, aluminum, gold, and silver. General metal materials such as SUS 304L stainless steel, SUS 36L stainless steel, and cobalt-chromium alloys are all of this type. The metal piece buried in the hard tissue does not fuse with the bone cells. When the removal test is performed a few weeks later, it is smooth and removed without resistance.
The third group has the smallest reaction with the organism. When implanting and attaching, titanium (Ti), zirconium (Zr), niobium (Nb), tantalum (Ta), and platinum (Pt) are suitable. When these metals are implanted and attached to organisms, they are closely combined with the cell tissues of hard tissues and soft tissues, showing an integration phenomenon.
As a result, titanium is definitely less harmful to organisms, and it is a safe metal. When using titanium alloy, according to the alloy elements used, the corrosion resistance is lower than that of pure titanium. When corrosion occurs, its elements can be dissolved out. For alloying elements, it is necessary to select those with corrosion resistance and non-injury properties. Among the titanium alloys, Ti-6AI-4V alloy has been used in aircraft manufacturing and seawater-resistant engineering equipment for a long time, and there are a large number of application examples. In the medical industry, ELI alloys with good corrosion resistance (with low iron, oxygen, and hydrogen content) have been introduced. However, recently, as the research and development of titanium alloy for implantation and placement, according to the report of the damage of the single body, the non-harmful niobium (Nb) is substituted for vanadium (V), and the Ti-13Nb-13Zr alloy has been standardized. (ASTM, ISO). There are also alloys that are acclaimed and actively discharging aluminum, which will be launched soon.
2. Types of titanium materials for medical use
The American ASTM standard (F code) for medical use is equivalent to the world standard in Europe. The ISO standard and the ASTM standard are combined as a European standard. Japan is sorting out domestic standards, taking ASTM and ISO corresponding standards to sort out, and starting to formulate standards based on ISO standards.
As artificial knee joints, hip joints (including femoral heads), etc., the titanium materials specified in the ASTM standard used in implants and attachments are listed in Table 1 according to their shapes. For a long time, pure titanium and Ti-6AI-4V alloy, including powder materials, have been made into parts and parts of various shapes.
3. Application examples of medical titanium materials
The places where titanium is used a lot are artificial femoral joints, artificial knee joints, bone plates, etc., which are suitable for plastic surgery. Severe pain caused by rheumatism [transliterated as "Lumaqizimu", which means a kind of severe joint and muscle pain, but also a kind of allergic disease-translator's note] and other reasons, resulting in It causes difficulty in walking. Patients suffering from this disease undergo artificial hip joint and artificial knee joint replacement surgery, which can completely eliminate the pain and can walk. In Japan, 80,000 artificial hip replacements and 40,000 artificial knee replacements are performed in one year (statistics in 2005). With the advent of the aging society in the future, we can predict what percentage growth rate will be used to meet this demand.
Titanium is not suitable for all artificial joints. In the joints, the parts that often swing are not suitable because titanium is easy to wear (ceramics and cobalt alloys should be used), and titanium alloys should be used for implant components. In order to be able to combine with the biological bone as soon as possible, the surface of the titanium alloy should be uneven and coated with osteosensor such as apatite and bioglass. In addition, intramedullary nails made of titanium alloy and titanium alloy plates are used for fracture fixation. Figure 3 shows various examples of implantation and placement.
There is also an increasing trend in the field of dentistry, the use of implants and attachments. The amount of titanium used is relatively small. There are pure titanium, titanium alloy, and shape memory alloy TiNi. Its shapes are as shown in Figure 4, such as plate type, thread type, sleeve type, and basket type. These parts and components are directly driven into the implanted gingival part to be fixed in the jawbone and coated with apatite representing bone components. Titanium is very suitable for metal implants in general dentistry. There are two methods: precision casting and superplastic forming. Compared with the previous use of cobalt and chromium alloys, it is lighter in weight and does not produce any taste of acidic food. Since the use of titanium is outside the health insurance diagnosis and treatment, the price quite expensive.
As an implant (embedded) and accessory for internal medicine, when the patient has a low heart rate, a pacemaker (Pacemaker - automatic ventricular contraction device) can be implanted (embedded) to stimulate the heart. The device to ensure the normal number of heart beats-translator's note), from the subclavian vein to the heart embedded electrode wire, from this electrode to the cardiac pacemaker input electronic signal, it becomes a cardiac pacemaker. Recently, the quality of the pacemaker product is 20g and the thickness is 6mm. It is so small that it is connected with the electrode wire and buried under the skin. The battery and the control circuit are packed in a small container (small box), this small container is a pure titanium product that is not harmful to live organisms. The battery life among them must be kept at a minimum of 6 years, so long-term stability and safety are required for this small container (small box). At present, nearly 5,000 people in Japan have been favored.
Among surgical instruments, the results of titanium cation can also be seen. Especially in the long-term neurosurgery operation of more than 10 hours, a forceps is also required to be lightweight, and the hemostatic forceps are all made of titanium. Many dental implants, surgical instruments for placement, and vibrators to remove tartar are made of titanium. In addition to implantation (buried) and attachment purposes, such as assistive equipment and wheelchairs are also titanium. When a part of the limbs is defective due to illness or an accident, a prosthesis must be made in order to restore the function. Because the main part is made of metal, it is from lightweight, durability (mainly corrosion resistance and fatigue damage), to In terms of biological compatibility (Ni, Cr, etc.), it is being applied. In terms of wheelchairs, the main goal is to reduce the weight of the entire wheelchair. Therefore, some of the structures, such as the frame and wheels, and almost all metal parts, are made of titanium.
