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Cobalt-based alloys for biomedical applications
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With the rapid development of the current social health industry, medical metal materials research has become a major hotspot in the global materials industry today. At present, the clinical application of medical metal materials are mainly stainless steel, cobalt-based alloys, titanium and titanium alloys, nickel-titanium shape memory alloys, etc., from the corrosion resistance and mechanical properties of the comprehensive measure, cobalt-based alloys is one of the most excellent materials, with good biocompatibility, high strength, good toughness, high bending fatigue strength and excellent processing performance and other advantages, as well as there are many other irreplaceable medical materials. Excellent performance.
Medical cobalt-based alloys generally contain cobalt, chromium, nickel, molybdenum, tungsten and other elements, chromium can form a dense oxide layer on the surface of the alloy, which can improve the corrosion resistance of the alloy, chromium can form a carbide, carbide has a high hardness, which can improve the strength of the matrix, and at the same time, may increase the alloy's abrasion resistance. The molybdenum element in the alloy is solidly dissolved in the matrix and can be a barrier to dislocation flow, thus increasing the strength of the matrix.
Medical cobalt-based alloys include CoCrMo alloys, CoCrMoW alloys, CoCrWNi alloys, CoNiCrMoWFe alloys and MP35N cobalt-nickel alloys and their baked porcelain alloys.
Development and application of cobalt-based alloys
The earliest developed cobalt alloy for medical use is cobalt-chromium-molybdenum (CoCrMo) alloy, whose structure is austenitic, and in the 70's the forged cobalt-nickel-chromium-molybdenum-tungsten-iron (CoNiCrMoWFe) alloy with good fatigue properties and the MP35N cobalt-nickel-chromium-molybdenum alloy with a multi-phase organization were also developed.
The first medical use of cobalt-based alloys was in the production of dental implants because of their excellent resistance to degradation in the oral environment, and the results of their various in vitro and in vivo tests showed that the alloys were biocompatible and suitable for use as surgical implants. Through continuous research and technological advances, cobalt-based alloys are gradually being used to make artificial hip and knee joints, joint buckles, splints, bone nails and bone pins.
Related research on cobalt-based alloys in the medical field
01、Copper-containing cobalt-based alloy antimicrobial performance research
Medical cobalt-based alloys as implant materials, the surface of the implant is prone to adhere to a large number of bacteria, thus inducing serious infections, for this reason, many scientists have been trying to solve the problem of bacterial infections from the perspective of implant materials. One approach is to modify the surface of the material to inhibit the formation of bacterial biofilm, e.g., by coating with antibiotic-containing polymers or ion-implanting strong antimicrobial metal elements. However, surface modifications are prone to fail quickly due to surface abrasion or peeling of the antimicrobial coating, and these coated implants will lose their antimicrobial function during use. Therefore, it is important to develop new biomedical materials with their own antimicrobial function. Some studies have shown that the addition of an appropriate amount of Cu in medical CoCrWNi alloy can release the strong antibacterial effect of Cu ions, so that it has strong antibacterial properties, the addition of Cu makes the corrosion current density of the alloy increased slightly, the experimental data show that the Cu-containing CoCrWNi alloy of Escherichia coli and Staphylococcus aureus inhibition rate of more than 90%, and can obviously inhibit the use of Cu-containing CoCrWNi alloys. CoCrWNi alloy can significantly inhibit the formation of bacterial biofilm on the surface of CoCrWNi alloy, which has a good prospect for clinical application.
02, cobalt-chromium alloy additive manufacturing technology for biomedical applications
Cobalt-chromium alloy has high strength and toughness, its mechanical and metallurgical properties and the ability to produce difficult-to-cut materials has a significant impact on the biomedical field of the requirements of the device components are also more delicate, so its manufacturing process is critical. Additive manufacturing technologies are widely used to produce products directly from digital models, they can be generated to the exact size, shape and even texture of many biological tissues, with design flexibility, part complexity, lightweighting, component integration, and functional design, so they can be accurately matched to patient needs. Comparative analysis of different additive manufacturing techniques used to fabricate cobalt chromium alloy biomedical components and implants shows that selective laser melting is a more appropriate technique in the biomedical field, as evidenced by the current research of many scholars.
03、Cobalt-based alloy research in orthopedics
With the increasing number of various implantable devices (such as orthopedic, cardiovascular, dental and ophthalmic implants), metal materials for biomedical applications are becoming increasingly important. In addition to titanium-based alloys and stainless steel, CoCrMo alloys are one of the most important materials used in orthopedic applications (i.e., total hip arthroplasty). The use of implantable hip replacements has been effective in improving the lifestyles of the elderly and in realizing an increase in average life expectancy. Initially, the average life expectancy of hip replacement devices was about 10-15 years, and some researchers have set the goal of extending the life expectancy to about 25-30 years, which is comparable to the life expectancy of metal-to-metal (MoM) hip replacement devices.
04. Discharge plasma sintered cobalt-chromium-based alloys for biomedical applications
Cobalt-chromium alloys with Nb and Mo contents of 3% and 3.5%, respectively, were prepared by discharge plasma sintering, and the results of the study showed that CoCr3.5Mo3.5Nb has the characteristics of biocompatibility and high strength, which is suitable for orthopedic implants and dental restorations; CoCr3Mo3Nb has a high degree of ductility, which is a property that plays a vital role in biomedical applications, making the material able to withstand mechanical strain, which can effectively alleviate the occurrence of stress fracture. At the same time, ductility also plays a vital role in dental restorations, enabling the restorations to withstand the forces exerted during mastication, thus maintaining their ability to withstand compressive, tensile and shear loads without fracture.
Conclusion
Metallic biomedical materials have a long history of application, and in recent years biomedical cobalt-based alloys have been widely used in clinical care and scientific research. However, the physiological environment in which biomedical cobalt-based alloy castings are placed is corrosive, which causes diffusion of metal ions to the surrounding tissues and degradation of the implanted material's own properties, the former of which may lead to toxic side effects, and the latter of which may lead to implanted material failure. Therefore, the research and development of new cobalt-based alloy biomedical materials with better performance and biocompatibility, as well as the processing and manufacturing methods, is a goal that researchers should continuously pursue.
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