다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Human tissue is structured mainly of self-assembled polymers (proteins) and ceramics (bone minerals), with metals present as trace elements with molecular scale functions. However, metals and their alloys have played a predominant role as structural biomaterials in reconstructive surgery, especially orthopedics, with more recent uses in non-osseous tissues, such as blood vessels. With the successful routine use of a large variety of metal implants clinically, issues associated with long-term maintenance of implant integrity have also emerged. This review focuses on metallic implant biomaterials, identifying and discussing critical issues in their clinical applications, including the systemic toxicity of released metal ions due to corrosion, fatigue failure of structural components due to repeated loading, and wearing of joint replacements due to movement. This is followed by detailed reviews on specific metallic biomaterials made from stainless steels, alloys of cobalt, titanium and magnesium, as well as shape memory alloys of nickel–titanium, silver, tantalum and zirconium. For each, the properties that affect biocompatibility and mechanical integrity (especially corrosion fatigue) are discussed in detail. Finally, the most critical challenges for metallic implant biomaterials are summarized, with emphasis on the most promising approaches and strategies.

Metallic implant biomaterials

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Development of new metallic alloys for biomedical applications

Young's modulus as well as tensile strength, ductility, fatigue life, fretting fatigue life, wear properties, functionalities, etc., should be adjusted to levels that are suitable for structural biomaterials used in implants that replace hard tissue. These factors may be collectively referred to as mechanical biocompatibilities. In this paper, the following are described with regard to biomedical applications of titanium alloys: the Young's modulus, wear properties, notch fatigue strength, fatigue behaviour on relation to ageing treatment, improvement of fatigue strength, fatigue crack propagation resistance and ductility by the deformation-induced martensitic transformation of the unstable beta phase, and multifunctional deformation behaviours of titanium alloys.

Mechanical biocompatibilities of titanium alloys for biomedical applications.

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The adhesive strengths between sol-gel fabricated hydroxyapatite (HAp) films and Ti­29Nb­13Ta­4.6Zr alloy (TNTZ) were evaluated before and after immersion in Ringer’s solution at 310K for 7 d. The effect of the surface morphology of TNTZ on the adhesion of HAp films was also investigated. The fracture surfaces after adhesion tests were observed and fracture areas at the interface between HAp films and TNTZ were also evaluated before and after immersion in Ringer’s solution. No significant differences in the adhesive strengths between HAp films and TNTZ disks with mirror-polished and mechanically polished surfaces were found. The fracture area at the interface between HAp film and mirror-polished TNTZ disk increases after immersion in Ringer’s solution, whereas no fracture occurs at the interface between HAp film and mechanically polished TNTZ disk before and after immersion in Ringer’s solution. It is supposed that Ringer’s solution penetrates along the cracks that are formed in the HAp films during calcination and the regions with weak adhesion between HAp and TNTZ are connected during immersion in Ringer’s solution in the case of HAp films fabricated on mirror-polished TNTZ. From these results, it is found that a relatively rougher surface is effective in improving the adhesion of HAp films fabricated on TNTZ before and after immersion in Ringer’s solution. [doi:10.2320/matertrans.M2015223]

Evaluation of Adhesion of Hydroxyapatite Films Fabricated on Biomedical β-Type Titanium Alloy after Immersion in Ringer’s Solution

Welding is an important technology for using titanium alloy plates in aerospace applications. However, pores (welding defects) are introduced into the welded zone during welding, including during the melting process, leading to a decrease in the fatigue strength of the welded titanium alloy joint. Friction stir welding (FSW) seems to be effective for avoiding the deterioration of fatigue strength because it is difficult for pores to form in the welded zone during FSW, which does not include a melting process. Therefore, the microstructure and mechanical properties, including the fatigue properties, of an (α + β)-type titanium alloy, Ti-4.5Al-2.5Cr-1.2Fe-0.1C alloy (Ti-531C), subjected to FSW were investigated. In this study, FSW was conducted from both sides of the plates (double-sided FSW) to ensure that the samples were subjected to the same experimental conditions (plate thickness, specimen geometry, etc.) used in our previous study on laser-welded Ti-531C plates for comparison. No pores are observed on the fractured surfaces of Ti-531C subjected to double-sided FSW. Consequently, higher fatigue strength is obtained for Ti-531C subjected to double-sided FSW compared with the samples subjected to double-sided laser welding. However, an acicular secondary α phase and a grain-boundary α phase in the first welded zone are coarsened by heating in the second welded zone, leading to a difference in hardness in the direction of the loading axis for the fatigue test. As a result, the boundary between these two regions became a stress-concentration site that deteriorates the fatigue strength of Ti-531C subjected to double-sided FSW.

Microstructure and fatigue properties of double-sided friction stir welded Ti-4.5Al-2.5Cr-1.2Fe-0.1C alloy plate for aerospace applications

Effect of grain diameter on Young’s modulus and tensile properties was investigated using a representative titanium alloy with self-tunable Young’s modulus, Ti-12Cr alloy for use in spinal fixation devices. The grain diameter can be changed systematically by changing solution-treatment temperature. With increasing grain diameter, the changes in Young’s moduli of the alloys subjected to solution treatment are negligible. Additionally, with increasing grain diameter, the increases in Young’s modulus during deformation are almost same. It indicates that the deformation-induced ω phase transformation is not sensitive to the grain diameter. Further, the strengths of the alloys decrease slightly, while the ductility of the alloys decreases drastically as increases in grain diameter. Therefore, a small grain diameter is preferred for developing new titanium alloys with changeable Young’s modulus for use in spinal fixation devices.

Mechanical properties of Ti-12Cr alloy with self-tunable Young's modulus for use in spinal fixation devices

New titanium alloys have been developed for use in next-generation aircrafts by adding low-cost elements such as C, Fe, Al and Cr. Some of the newly developed alloys are Ti-4.5Al-2Mo-1.6V-0.5Fe-0.3Si-0.03C, referred to as KS Ti-9, and Ti-4.5Al-2.5Cr-1.2Fe-0.1C, referred to as KS Ti-531C. As opposed to the widely used Ti-6Al-4V (Ti64), KS Ti-9 can be rolled at much lower temperatures without employing pack-rolling, and the anisotropy in its mechanical strength is significant. Microstructural control process to reduce the anisotropy in the mechanical strength of KS Ti-9 has been investigated. Anisotropy controlling treatment (ACT) is found to be effective to reduce the anisotropy in the mechanical strength of KS Ti-9.

Microstructural Control and Mechanical Properties of Low-Cost Titanium Alloys for Next Generation Aircrafts

Young’s moduli of metallic biomaterials for implant devices such as artificial hip joints, bone plates, intramedullary rods, and rods for spinal fixation devices should be similar to that of cortical bone to prevent stress shielding [1].

Masaaki Nakai

Papers

Evaluation of Adhesion of Hydroxyapatite Films Fabricated on Biomedical β-Type Titanium Alloy after Immersion in Ringer’s Solution

Microstructure and fatigue properties of double-sided friction stir welded Ti-4.5Al-2.5Cr-1.2Fe-0.1C alloy plate for aerospace applications

Mechanical properties of Ti-12Cr alloy with self-tunable Young's modulus for use in spinal fixation devices

Microstructural Control and Mechanical Properties of Low-Cost Titanium Alloys for Next Generation Aircrafts

Low-Young’s-Modulus Materials for Biomedical Applications