Development and application of medical titanium alloy
Medical titanium alloy development history
In the early 1940s, research and development of titanium alloys began to progress gradually. Bothe et al. used titanium in mouse bone and found that the compatibility of the rat bone with titanium was good and no adverse reaction occurred. In the 1950s and 1960s, titanium alloys with high temperature resistance were developed. In the early 1970s, a group of corrosion resistant titanium alloys were successively improved. In the mid-1980s, the second generation of vanadium-free a + β titanium alloys (Ti-6Al-7Nb and Ti-5Al-2.5Fe) have also been developed and have been used clinically for a long time. However, Al and Fe, which are toxic elements in the alloy, will cause some harm to the human body. The elastic modulus also falls short of the true femur standard, resulting in "stress shielding" that causes bone resorption around the implant, causing the implant to break or become loose, resulting in failure of implantation. By the beginning of 1990, the United States and Japan began to devote themselves to the study of the third generation of new medical titanium alloys, of which β-type titanium alloys were the principal ones.
As a new type of alloy, titanium alloy is also a kind of carrier material, which is commonly used in the related fields of limb implantation, alternative functional materials, dentistry, medical equipment and so on. Titanium and titanium alloys are: Good corrosion resistance, high strength, low modulus of elasticity, fatigue resistance, good biocompatibility and so on. It's good biocompatibility makes it uniquely superior to other metals and is therefore favored in the medical field but due to its low abrasion resistance and poor process performance. It is committed to further improvements to keep going.
Beta titanium alloy research and development
Preparation principle and design of alloy
(1) the choice of titanium
In the choice of medical materials to adapt to different parts, the material elasticity modulus, toughness, strength, corrosion resistance and other related indicators to become an essential factor to consider. Yu Zhentao et al. compared different metal elements for experiments. The results of their research are as follows: V, Co, Cd, Cr, Ni, Hg and other elements are more toxic. Followed by Fe and Al. In organisms such as spleen, liver, kidney and other parts of the discovery of V ion precipitates, its greater biological toxicity; and Al elements will also be in the form of Al salt accumulation in the body resulting in the body's nervous system disorders and the corresponding organ damage. Elements such as Ta, Mo, Zr, Sn, Pd, Hf, Nb have good biocompatibility and can be used as additional elements for the alloys. The chemical stability of Mo, Sn, Zr, TaHf, Nb, Pd is good, and Ta, Nb, Zr, Mo can reduce the elastic modulus of the alloy, and thus can effectively improve the stability of the alloy. In summary, ideal alloys for biomedical titanium alloys include Ti-Mo-Nb, Ti-Zr-Nb, Ti-Zr-Mo-Nb and Ti-Zr-Sn-Mo-Nb.
(2) titanium alloy design
In the alloy design process, d electronic design theory for the basic method of alloy design. The basic idea is: By calculating the electron orbital parameters of Ti and its added elements, the corresponding Md Value and Bo value are obtained, and then the relevant parameters such as the elastic modulus and tensile strength of the alloy are analyzed. Experiments show that the lower Md value is conducive to phase stability. Higher Bo value is conducive to enhancing the strengthening effect of the solution. In the design of metastable β-type titanium alloy, Md value should be controlled 2.35 ~ 2.45 and the Bo value is between 2.75 ~ 2.85. The thermostable β-type titanium alloy will undergo a slip deformation when subjected to plastic working, while the metastable β-type titanium alloy may slip, martensite or twin deformation (Figure 1). Thus by controlling the unique alloy microstructure can make the material properties in a wide range can be improved.
4 titanium alloy development status
(1) β titanium alloy of low elastic modulus
The United States has developed a variety of low modulus beta titanium alloys, Ti-13Mo-7Zr-3Fe and Ti-35Nb-7Zr-5Ta can be used as an ideal replacement hip joint, Ti-13Mo-7Zr-3Fe alloy which has closer to The low elastic modulus of the human skeleton standard, can reduce the "stress shielding" effect, which can effectively reduce the bone damage caused by implantation. Russia also promoted a new medical titanium alloy Ti51-Zr18Nb, its elastic modulus of elasticity is only 47Gpa, and its reversible deformation is as high as 2.83%. In Japan, the β-titanium alloy with low elastic modulus needs to be further improved. The TNTZ alloy undergoes large plastic deformation under high-pressure torsion, and the tensile strength of the alloy is likewise greatly improved.
(2) Shape memory alloy
Shape memory alloy with deformation recovery, the function from the thermoplastic martensitic transformation. The martensite in the memory alloy will change correspondingly with the change of the temperature. The austenite phase appears at high temperature and the martensite phase at low temperature. Its shape memory effect also includes: one-way memory effect, two-way memory effect and full memory effect. In addition, the shape memory alloy also has a large amount of bending, high plasticity. Therefore, in the therapeutic field, it can be used to prepare memory NiTi dental arch wire, shape memory alloy blood filter and cannula-linked aluminum alloy prosthesis.
(3) porous titanium alloy
In order to address this problem, the appearance of porous titanium alloy improves the performance of implants because the looseness and fracture of implants caused by the "stress shielding" effect restrict the application of titanium and its alloys. By adjusting the size of the porosity, the elastic modulus, strength and density of the alloy can be biocompatible with the replaced tissue for better matching; in addition, the porous structure and the rough surface enable Cell adhesion, is conducive to proliferation and differentiation; holes can become the body of nutrients and body fluids transport channel is conducive to the re-growth of tissue cells to speed up the healing process. Therefore, the advantages of porous titanium alloy are widely studied in medicine.
(4) titanium alloy surface modification
Although titanium alloy has excellent biocompatibility, it belongs to bio-inert material. Low wear resistance, easy to generate a large number of wear debris containing titanium wear, and even induce inflammation, resulting in the dissolution of bone tissue around the implant, greatly reducing its service life. Surface modification of titanium alloy can retain the original titanium alloy excellent performance, based on its biocompatibility, abrasion resistance, corrosion resistance and other aspects to enhance and improve its clinical performance so as to better play its use value. There are numerous kinds of titanium alloy surface modification methods, including oxidation modification, vapor deposition, ion implantation, plasma spraying and laser surface modification.
5. Medical titanium alloy applications
(1) Dentistry
Titanium and human connective tissue, bone epithelial tissue has good affinity, excellent mechanical properties also reflect its strengths in medical alloys. And the density of small, lightweight, good corrosion resistance, wearing comfortable, therefore, titanium as a denture (implant) received a wide range of favored. In addition, titanium dentures through the surface treatment, the appearance of increased performance, to meet the public demand for the United States, giving a visual enjoyment.
(2) limb correction
Depending on the literature, about 100 million patients worldwide each year suffer from inflammation related to the knee joint and arm joints. It is essential to carry out replacement surgery. Therefore, the titanium alloy with exceptional replacement function brings good news. Report to ceramic, stainless steel and other materials, the elastic modulus of titanium alloy closer to human bones, the modulus size is more advantageous. Therefore, titanium alloy in the ankle, elbow and other corrections are widely used. In addition, the porous titanium alloy material can make the prosthesis bioactive, contribute to the healing of the femoral head; titanium alloy surface biocompatibility is good, can induce bone cell growth, so by clinicians, orthopedic field experts are respected.
(3) implant repair and replacement
Implants, titanium and titanium alloys as the implant repair advantages are: ① high strength, chemical stability and good biocompatibility; ② non-toxic, will not cause harm to the human body; ③ low-modulus of elasticity, And human bones more matching; ④ memory alloy has the resilience and shape recovery. In summary, the application of titanium in the skull repair mainly reflected in: the use of titanium mesh can repair the defect in the skull. In the human cardiovascular application is reflected in: the preparation of artificial heart valves, blood filters, pacemakers and artificial heart pumps.
