No abstract

No abstract

Designing materials having suitable mechanical properties and targeted degradation behavior is the key for the development of biodegradable materials for medical applications, including stents. A series of Fe-Mn alloys was developed with the objective to obtain mechanical properties similar to those of stainless steel 316L and degradation behavior more suited than pure iron. Four alloys with Mn content ranging between 20 and 35 wt % were compared in this study. Their microstructure, mechanical properties, magnetic properties as well as degradation behavior were carefully investigated. Results show that their microstructure is mainly composed of gamma phase with the appearance of epsilon phase in alloys having a lower Mn content. The yield strength and elongation of alloys was comprised between 234 MPa and 32% for Fe-35%Mn alloy to 421 MPa and 7.5% for the Fe-20%Mn alloy. All alloys show similar magnetic susceptibility ( approximately 1.8 x 10(-7) m(3)/kg) in the quenched condition. This magnetic susceptibility remains constant after plastic deformation for all the tested alloys except for the Fe-20%Mn alloy. The corrosion rate was higher than pure iron. Among the alloys studied in this work, the Fe-35%Mn alloy shows mechanical properties and degradation behavior closely approaching those required for biodegradable stents application.

Absorbable metals, metals that corrode in physiological environment, constitute a new class of biomaterials intended for temporary medical implant applications. The introduction of these metals has shifted the established paradigm of metal implants from preventing corrosion to its direct application. Interest toward absorbable metals has been growing in the past decade. This is proved by the rapid increase in scientific publication, progressive development of standards, and launching the first commercial products. Iron, magnesium, zinc, and their alloys are the current three absorbable metals families. Magnesium-based metals are the most progressing family with a large data set obtained from both basic and translational research. Iron-based metals are still facing a major challenge of low in vivo corrosion rate despite the significant efforts that have been put to overcome its weakness. Zinc-based metals are the new alternative absorbable metals with moderate corrosion rates that fall between those of iron and magnesium. This manuscript provides a brief review on the latest progress in the research and development of absorbable metals, the most important findings, the remaining challenges, and the perspective on the future direction.Graphical abstract

An Fe-35 wt-%Mn alloy, aimed to be used as a metallic degradable biomaterial for stent applications, was prepared via a powder metallurgy route. The effects of processing conditions on the microstructure, mechanical properties, magnetic susceptibility and corrosion behaviour were investigated and the results were compared to those of the SS316L alloy, a gold standard for stent applications. The Fe35Mn alloy was found to be essentially austenitic with fine MnO particles aligned along the rolling direction. The alloy is ductile with a strength approaching that of wrought SS316L. It exhibits antiferromagnetic behaviour and its magnetic susceptibility is not altered by plastic deformation, providing an excellent MRI compatibility. Its corrosion rate was evaluated in a modified Hank's solution, and found superior to that of pure iron (slow in vivo degradation rate). In conclusion, the mechanical, magnetic and corrosion characteristics of the Fe35Mn alloy are considered suitable for further development of a new class of degradable metallic biomaterials.

No abstract

Biomedical Engineering -From Theory to Applications 412 visible under X-ray imaging. Most of artificial implants are subjected to loads, either static or repetitive, and this condition requires an excellent combination of strength and ductility. This is the superior characteristic of metals over polymers and ceramics. Specific requirements of metals depend on the specific implant applications. Stents and stent grafts are implanted to open stenotic blood vessels; therefore, it requires plasticity for expansion and rigidity to maintain dilatation. For orthopaedic implants, metals are required to have excellent toughness, elasticity, rigidity, strength and resistance to fracture. For total joint replacement, metals are needed to be wear resistance; therefore debris formation from friction can be avoided. Dental restoration requires strong and rigid metals and even the shape memory effect for better results. In overall, the use of biomaterials in clinical practice should be approved by an authoritative body such as the FDA (United States Food and Drug Administration). The proposed biomaterial will be either granted Premarket Approval (PMA) if substantially equivalent to o n e u s e d b e f o r e F D A l e g i s l a t i o n o f 1 9 7 6 , o r h a s t o g o t h r o u g h a s e r i e s o f g u i d e d biocompatibility assessment. Common metals used for biomedical devicesUp to now, the three most used metals for implants are stainless steel, CoCr alloys and Ti alloys. The first stainless steel used for implants contains ~18wt% Cr and ~8wt% Ni makes it stronger than the steel and more resistant to corrosion. Further addition of molybdenum (Mo) has improved its corrosion resistance, known as type 316 stainless steel. Afterwards, the carbon (C) content has been reduced from 0.08 to 0.03 wt% which improved its corrosion resistance to chloride solution, and named as 316L. Titanium is featured by its light weight. Its density is only 4.5g/cm 3 compared to 7.9g/cm 3 for 316 stainless steel and 8.3g/cm 3 for cast CoCrMo alloys (Brandes and Brook, 1992). Ti and its alloys, i.e. Ti6Al4V are known for their excellent tensile strength and pitting corrosion resistance. Titanium alloyed with Ni, i.e. Nitinol, forms alloys having shape memory effect which makes them suitable in various applications such as dental restoration wiring. In dentistry, precious metals and alloys often used are Au, Ag, Pt and their alloys. They possess good castability, ductility and resistance to corrosion. Included into dental alloys are AuAgCu system, AuAgCu with the addition of Zn and Sn known as dental solder, and AuPtPd system used for porcelain-fused-to-metal for teeth repairs. CoCr alloys have been utilised for many decades in making artificial joints. They are generally known for their excellent wear resistance. Especially the wrought CoNiCrMo alloy has been used for making heavily loaded joints such as ankle implants (Figure 1). Other metals used for implants include tantalum (Ta), amorphous alloys and biodegradable metals. Tantalum which has excell...

Scaffolds have been utilized in tissue regeneration to facilitate the formation and maturation of new tissues or organs where a balance between temporary mechanical support and mass transport (degradation and cell growth) is ideally achieved. Polymers have been widely chosen as tissue scaffolding material having a good combination of biodegradability, biocompatibility, and porous structure. Metals that can degrade in physiological environment, namely, biodegradable metals, are proposed as potential materials for hard tissue scaffolding where biodegradable polymers are often considered as having poor mechanical properties. Biodegradable metal scaffolds have showed interesting mechanical property that was close to that of human bone with tailored degradation behaviour. The current promising fabrication technique for making scaffolds, such as computation-aided solid free-form method, can be easily applied to metals. With further optimization in topologically ordered porosity design exploiting material property and fabrication technique, porous biodegradable metals could be the potential materials for making hard tissue scaffolds.