Magnesium and its alloys as orthopedic biomaterials: a review.

http://www.uniroma2.it/didattica/tbs2/deposito/Manufacture,_characterisation_and_application_of_cellular_metals_and_metal_foams.pdf

Manufacture, characterisation and application of cellular metals and metal foams

Titanium and titanium alloys are widely used in biomedical devices and components, especially as hard tissue replacements as well as in cardiac and cardiovascular applications, because of their desirable properties, such as relatively low modulus, good fatigue strength, formability, machinability, corrosion resistance, and biocompatibility. However, titanium and its alloys cannot meet all of the clinical requirements. Therefore, in order to improve the biological, chemical, and mechanical properties, surface modification is often performed. This article reviews the various surface modification technologies pertaining to titanium and titanium alloys including mechanical treatment, thermal spraying, sol–gel, chemical and electrochemical treatment, and ion implantation from the perspective of biomedical engineering. Recent work has shown that the wear resistance, corrosion resistance, and biological properties of titanium and titanium alloys can be improved selectively using the appropriate surface treatment techniques while the desirable bulk attributes of the materials are retained. The proper surface treatment expands the use of titanium and titanium alloys in the biomedical fields. Some of the recent applications are also discussed in this paper.

/pdf/surface-modification-of-titanium-titanium-alloys-and-related-176rvxu9wp.pdf

Surface modification of titanium, titanium alloys, and related materials for biomedical applications

Protective coatings on magnesium and its alloys — a critical review

The use of electric current to activate the consolidation and reaction-sintering of materials is reviewed with special emphasis of the spark plasma sintering method. The method has been used extensively over the past decade with results showing clear benefits over conventional methods. The review critically examines the important features of this method and their individual roles in the observed enhancement of the consolidation process and the properties of the resulting materials.

/pdf/1000-at-1000-the-effect-of-electric-field-and-pressure-on-vmcyq57hsf.pdf

1000 at 1000: The effect of electric field and pressure on the synthesis and consolidation of materials: a review of the spark plasma sintering method.

Processing of biocompatible porous Ti and Mg

Compressibility of porous magnesium foam: dependency on porosity and pore size

Pure titanium and some of its alloys are currently considered as the most attractive metallic materials for biomedical applications due to their excellent mechanical properties, corrosion resistance, and biocompatibility. It has been demonstrated that titanium and titanium alloys are well accepted by human tissues as compared to other metals such as SUS316L stainless steel and Co–Cr–Mo type alloy. In the present study, highly porous titanium foams with porosities ≤80% are produced by using a novel powder metallurgical process, which includes the adding of the selected spacers into the starting powders. The optimal process parameters are investigated. The porous titanium foams are characterized by using optical microscopy and scanning electron microscopy. The distribution of the pore size is measured by quantitative image analyses. The mechanical properties are investigated by compressive tests. This open-cellular titanium foams, with the pore size of 200–500 μm are expected to be a very promising biomaterial candidates for bone implants because its porous structure permits the ingrowths of new-bone tissues and the transport of body fluids.

Processing and mechanical properties of autogenous titanium implant materials

Titanium foams fabricated by a new powder metallurgical process have bimodal pore distribution architecture (i.e., macropores and micropores), mimicking natural bone. The mechanical properties of the titanium foam with low relative densities of approximately 0.20-0.30 are close to those of human cancellous bone. Also, mechanical properties of the titanium foams with high relative densities of approximately 0.50-0.65 are close to those of human cortical bone. Furthermore, titanium foams exhibit good ability to form a bonelike apatite layer throughout the foams after pretreatment with a simple thermochemical process and then immersion in a simulated body fluid. The present study illustrates the feasibility of using the titanium foams as implant materials in bone tissue engineering applications, highlighting their excellent biomechanical properties and bioactivity.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400062087

Novel titanium foam for bone tissue engineering

Magnesium and magnesium alloys are being increasingly used in varied areas of industry due to their low densities from 1.75 to 1.85 g/cm 3 and high specific strength. These very light materials are particularly suitable for weight-saving constructions in aircraft industry, vehicle production, and portable electric devices. However, for many applications, magnesium and its alloys are inferior in corrosion and wear resistance due to their high reactivity and low hardness (HV60–80). In general, the hardness improvement by bulk alloying with other elements requires high quantities of additives. It may cause an increase in cost and density of alloys. Thus, surface treatments are frequently applied to practical applications as circumstances demand. As the surface hardening process, dry processes such as anodizing, plating, and PVD (physical vapor deposition) are frequently adopted on the mechanical parts and structural magnesium alloys [1]. In general, however, thin films produced by these processes are insufficient in machine parts used under harsh conditions. For example, vapor coatings by PVD are too thin to endure being under large stress. Plating has a problem that adherence strength of coating is so weak that there is possibility of peeling off. The stiffening layers of hundreds of microns are necessary so that wear and abrasion resistance are improved sufficiently. On the other hand, diffusion coating process is one of the promising methods of surface treatment since its adherence strength is high and it does not need any expensive equipment like PVD and CVD (chemical vapor deposition) [2–9]. In this research, in order to obtain a surface coating layer over hundreds-micron, diffusion coating was carried out on the AZ91D magnesium alloy. As a result, Al-Mg intermetallic compound layer of 750 μm was formed by a heat treatment o f 1 h in aluminum powder. The aluminum powder whose purity was 99.5% and whose particle diameter was 100 μm was used for the source of diffusion element. Furthermore, zirconia powder was mixed with aluminum powder so that sintering of aluminum powder was avoided. Magnesium specimens (AZ91D alloy), in form of 15 mm × 10 mm× 5 mm plate, were cut out from a cast ingot that had been performed a solid solution treatment at 420◦C for 20 h. Both the mixed powder of aluminum and AZ91D specimens were put into an alumina crucible together. The crucible was settled in a ceramic tube, and heating elements outside the tube heated the tube and the crucible. To avoid oxidation of specimens and powder in the crucible, pure argon gas (purity 99.995%) was flowed through the tube during the heat treatment. The heat treatment for diffusion coating was carried out at 450 ◦C for 1 h. The specimens were cooled down until 100 ◦C in the furnace, and were taken out to the air. After the processing, the surface of the specimen was analyzed by X-ray diffractometer to identify formed intermetallic compounds. The cross sections were observed with SEM (scanning electron microscope) and a composition analysis by EPMA (electron probe X-ray micro analyzer) was carried out. Furthermore, hardness distributions of depth

Koji Shimojima

Papers

Processing of biocompatible porous Ti and Mg

Compressibility of porous magnesium foam: dependency on porosity and pore size

Processing and mechanical properties of autogenous titanium implant materials

Novel titanium foam for bone tissue engineering

Surface treatment of AZ91D magnesium alloy by aluminum diffusion coating