Adaptability of titanium alloy materials to the human body and types of Medical Titanium

In the medical business, the use of metal materials must be absolutely harmless to the human body. When the metal corrodes, it can dissolve metal ions, which affects the cellular organization of the organism (human body), so it is necessary to use metal materials that are not easily corroded and highly corrosion-resistant, and titanium is a kind of highly corrosion-resistant material. Medical metal materials from stainless steel series to cobalt-based and titanium-based alloy series, titanium and titanium alloy ratio is increasing. The amount of titanium used in the medical industry worldwide is about 1,000 tons a year.

1. Adaptability of titanium to the human body (compatibility of Medical Titanium with living organisms)

In order to observe the response of metal ions to human adaptability, we conducted a cell adaptability evaluation method in the laboratory using cells sensitive to metal ions, such as mouse lung fibroblasts (V79 cells) and mouse (20-day-old mouse) fibroblast tissues (I929 cells), which are used for medical experiments in China, and were evaluated by the Independent Administrative Institution for the Evaluation of Products (IABE). We differentiate between the reactions of elemental monomer ions to the human body (living organisms) provided by the Technical Base Organization for Evaluation of Medical Devices (Technical Committee for Standardization of Biological Evaluation of Medical Devices). When titanium alloys are used, depending on the alloying elements used, the corrosion resistance of titanium alloys decreases compared with that of pure titanium alloys, and when corrosion occurs, the alloying elements can be dissolved. It is necessary to choose alloying elements that are corrosion-resistant and non-invasive. In titanium alloys, Titanium 6AL4V ELI has been used for a long time in airplane manufacturing and seawater-resistant engineering equipment, and has a large number of examples of use. In the medical field, ELI alloys, which have good corrosion resistance (low iron, oxygen, and hydrogen content), have been used for a long time. Recently, however, as part of the research and development of titanium alloys for implantation and placement, we have standardized the Ti-13Nb-13Zr alloy by replacing vanadium (V) with niobium (Nb), which is a non-injurious alloy, based on the report on the mutagenicity of the monomer (ASTM, ISO). There is also an alloy that is actively discharging aluminum, and it will be released soon.

2.Titanium for Medical Use

The American ASTM standard (F-code) for medical use is equivalent to the world standard, and in Europe, the ISO standard and the ASTM standard (ASTM F136 ASTM F67)are being sorted out and merged into the European standard. In Japan, we are organizing our domestic standards, and we are organizing the standards corresponding to ASTM and ISO, and we are starting to make standards based on the ISO standards.

The titanium materials specified in the ASTM standard for implants and attachments such as artificial knee joints and hip joints (including femoral heads) are listed according to their shapes. For a long time, pure titanium and Ti-6AI-4V alloys, including powdered materials, have been used to make various shapes of parts and components.

3.Medical titanium applications

Titanium is used in many parts such as artificial femoral joints, artificial knee joints, bone plates, etc. It is also used in orthopedic surgery. Titanium is not suitable for all artificial joint parts, in the joint part, often swinging part, because titanium is easy to wear and tear is not suitable (preferably use ceramic and cobalt alloy), and implanted parts to be used titanium alloy. The surface of the titanium alloy is unevened and coated with a bone-sensitive material such as apatite or bioglass in order to make it bond with the biological bone at an early stage. In addition, for fracture fixation, titanium intramedullary nails and titanium plates are used.

There is also an increasing trend in the field of dentistry, where implants and attachments are being used. Titanium is used in smaller quantities, but there are titanium alloys and pure titanium alloys in the form of plates, threads, sockets, and baskets as shown in the figure. These parts are driven directly into the jawbone and coated with apatite, which is representative of the composition of the bone, to be fixed in the gingival portion of the tooth. Titanium is suitable for metal implants in general dentistry. There are two methods of precision casting and superplastic molding, and it is lighter in weight and does not taste acidic food compared to the previous use of cobalt and chromium alloys, but the price is more expensive because the use of titanium belongs to the outside of the health insurance diagnosis and treatment.

As an implantable accessory for internal medicine, a pacemaker can be implanted when a patient suffers from a low heart rate. An electrode wire is inserted from the subclavian vein to the heart, and this electrode inputs an electronic signal to the pacemaker, making it a pacemaker. Recently, pacemakers have been developed with a mass of 20g and a thickness of 6mm, so they are small enough to be connected with an electrode wire and buried under the skin. The battery and the control circuitry are contained in a small container (locket) made of pure titanium, which is non-invasive to living organisms. The battery has to last at least 6 years, so the container (locket) is required to be stable and safe for a long time. Currently, nearly 5,000 people in Japan have been benefited.

Titanium is also used in surgical instruments. Especially in the case of long brain and neurosurgery operations lasting more than 10 hours, a forceps is required to be lightweight, and titanium products are used for hemostatic forceps. Titanium is also used in many dental treatment instruments such as implants, surgical instruments for attachments, and vibrators for removing tartar. In addition to implantation (embedding) and attachment, such as auxiliary equipment and wheelchairs, titanium is also being used. When a part of a limb is missing due to an illness or accident, a prosthesis is made to restore function, and since the main part of the prosthesis is made of metal, it is being used for lightweighting, durability (mainly corrosion and fatigue resistance), and compatibility with living organisms (Ni, Cr, etc.). In the case of wheelchairs, the main goal is to lighten the entire wheelchair, so in some cases, titanium is used for almost all metal parts in the structure, such as the frame and wheels.