Metals for Biomedical Applications

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...

The Determination of Abrasion Resistance of Selected Biomaterials for the Friction Pairs in the Hip Joint Endoprosthesis

“…It belongs to the group of metallic biomaterials, which was adapted to be implanted in the human body at the earliest. The steel 316 LVM, regarded as a medical grade, is characterized by low impurities contents by means of a vacuum melting technology [6,13,14]. It has excellent resistance to both general and intergranular corrosion, and pitting and crevice corrosion.…”

“…Therefore the use of the new generation Ti13Nb13Zr titanium alloy, free of toxic elements, for the endoprosthesis components has been proposed [6].…”

Classifications, Surface Characterization and Standardization of Nanobiomaterials

“…Metallic biomaterial includes stainless steel (St 316L), cobalt-chromium-molybdenum based alloy (Co-Cr-Mo), titanium alloy (Ti), gold and platinum. The applications of metallic biomaterials are used in many fields such as: cardiovascular (stent, heart artificial valve), orthopedic like bone fixation (plate, screw pin), and in artificial joints and dentistry (orthodontic wire, filling) [11]. Ceramic biomaterials include: alumina (AL 2 O 3 ), zirconia (ZrO 2 ), carbon calcium aluminates (Ca (Al 2 O 4 )).…”

Effects of Admixed Titanium on Densification of 316L Stainless Steel Powder during Sintering

“…Frazad et al has suggested that cracks initiated due to pitting and crevice corrosion are responsible for failure of bio-medical implants [7]. Corrosion of bio-medical implants can be minimized by improving the densification and developing the nano passive film of chromium oxide layer on 316L SS powder [8]. Powder metallurgy (PM) is one approach to fabricate denser and cost effective bio-implants required.…”