Titanium Screws

Titanium and titanium alloys are widely used as bone implant and dental restoration materials for medical titanium machined parts in recent years because of their low density, high specific strength, good corrosion resistance and biocompatibility. However, the elastic modulus of titanium and titanium alloys does not match natural bone, and their strength (tensile strength, compressive strength and flexural strength, etc.) is also much higher than that of human bone. Under stress, the material and bone will generate different strains, causing relative displacement at their interfaces, and the load cannot be completely transferred from the implant to the adjacent bone tissue, and the bone lacking sufficient stress stimulation will degrade, atrophy, or even be resorbed, eventually leading to loosening and fracture of the implant, which cannot meet the requirements for long-term use and limits its further application. More and more researchers at home and abroad are exploring ways to reduce the elastic modulus of titanium and titanium alloys in order to reduce or eliminate this "stress shielding" phenomenon and improve the biomechanical compatibility of titanium and titanium alloys.

Titanium alloy processing

In general, there are two ways to reduce the modulus of elasticity of titanium and titanium alloys: one is alloying, where the modulus of elasticity of B-type titanium alloys is lower than that of a-type titanium alloys. The lower elastic modulus available in titanium alloys so far has been reported to be about 40 GPa obtained in Ti-Nb.Sn system alloys, and it is very difficult to reduce it further to below 4 OGPa. However, the elastic modulus of cortical bone is 4.4 to 28.8 GPa, and cancellous bone is only 0.01 to 3.0 GPa_8, and alloying is limited to reduce the elastic modulus of titanium alloys. Another method is to introduce pore structure to obtain porous titanium and titanium alloy, whose mechanical properties such as density, modulus and strength can be adjusted to match the replaced bone tissue by adjusting the pores.

In addition, the unique porous structure and the rough inner and outer surfaces are conducive to the adhesion, proliferation and differentiation of osteoblasts, which promote the growth of new bone tissue into the pores and the formation of a biological fixation between the implant and the bone, and finally the formation of a whole; the open three-dimensional connecting pore structure enables the transfer of body fluids and nutrients in the porous implant, promotes tissue regeneration and reconstruction, and accelerates the healing process. Therefore, porous titanium and titanium alloys with the above characteristics are considered to be the most attractive bio-implant materials, and have become a hot spot for research on biomaterials in recent years.

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