Alumina implant material

Isotropic carbon is obtained by the pyrolysis of a hydrocarbon, usually methane, at high temperature (1200-1500°C) in a fluidized bed on a graphite substrate.Under these conditions, a turbostratic structure is obtained which is characterized by very little ordering and an essentially random orientation of small crystallites. In contrast to graphite which is highly anisotropic, such a structure has isotropic properties (see Ch. 7). Isotropic carbon is completely inert biologically. Its properties are compared to alumina, another common implant material, in Table 17.8. Notable is its high strain to failure. 

Implant materials for coating. Prosthetic materials coated with HAp include titanium, Ti-6A1-4V, stainless steel, Co-Cr-Mo, and alumina (Jiang and Shi 1998). These materials are roughened by grit blasting for a mechanical interlock between the melted component of the particle and the substrate. The Ti-6A1-4V and Cr-Co-Mo alloys are the most common. Ideally, the elastic modulus and co-efficient of thermal expansion of the substrate and the coating material will be matched to minimize any residual stresses at the interface. Hydroxylapatite (E = 100 GPa and a = 12 x 10 °C (Perdok et al. 1987)) is... 

An important requirement for any implant material is how long it will last. Because of the nature of failure of ceramic components it is not possible to provide a specific and definite lifetime for each individual implant. Rather we have to express failme in terms of probabilities. Figure 16.27 is an applied stress versus probability of time to failure (SPT) diagram for medical grade alumina. It shows that for a 30-year survival period with failure of no more than 1 in 100 components the maximum tensile stress that can be applied is limited to <200MPa. If stresses of... 

There are many other applications of alumina as an implant material including knee prostheses, ankle joints, elbows, shoulders, wrists, and fingers. 

Friction studies were carried out with a hip-joint simulator by Scholes et al. They compared the friction behavior between a number of implant materials using both carboxy methyl cellulose (CMC) solutions and biological fluids as lubricants. They found that friction coefficient for alumina/alumina was higher for biological fluids than for CMC, and attributed this to the inhibition of fluid-film formation by a protein film on the surfaces. For metal/ metal joints, the friction coefficients were lower in biological fluids, leading to the conclusion that the formation of a protein film assisted boundary lubrication. 

The adsorption of albumin, the most abundant protein in synovial fluid, on implant materials was studied in detail by means of XPS and I -labeUed albumin. These techniques showed the formation of a monolayer of albumin on alumina but multilayered islands of protein on the CoCrMo surface. No PE transfer was observed in AFM images of the surface of CoCrMo after tribological tests when an albumin solution was used as the lubricant. However, contrary to the studies described earlier, the addition of albumin to a solution of Hank s balanced salt solution caused a dramatic drop in the friction coefficient for UHMWPE sliding against CoCrMo. ... 

Li, P., Ohtsuki, C., Kokubo, T., Nakanishi, K, Soga, N. and de Groot, K (1994) The role ofhydrated silica, titania and alumina in inducing apatite on implants. Journal of Biomedical Materials Research, 28, 7-15. 

Considerable development has occurred on sintered ceramics as bone substitutes. Sintered ceramics, such as alumina-based ones, are uru eactive materials as compared to CBPCs. CBPCs, because they are chemically synthesized, should perform much better as biomaterials. Sintered ceramics are fabricated by heat treatment, which makes it difficult to manipulate their microstructure, size, and shape as compared to CBPCs. Sintered ceramics may be implanted in place but cannot be used as an adhesive that will set in situ and form a joint, or as a material to fill cavities of complicated shapes. CBPCs, on the other hand, are formed out of a paste by chemical reaction and thus have distinct advantages, such as easy delivery of the CBPC paste that fills cavities. Because CBPCs expand during hardening, albeit slightly, they take the shape of those cavities. Furthermore, some CBPCs may be resorbed by the body, due to their high solubility in the biological environment, which can be useful in some applications. CBPCs are more easily manufactured and have a relatively low cost compared to sintered ceramics such as alumina and zirconia. Of the dental cements reviewed in Chapter 2 and Ref. [1], plaster of paris and zinc phosphate... 

Alumina is a well-known bioinert ceramic material which can be used in total hip prosthesis and dental implants since it exhibits good biocompatibility, strength, and excellent corrosion resistance.70,71 The application of alumina has some limitations due to poor fracture toughness. The incorporation of ductile phase may lead to the... 

Porous anodic alumina is a very promising material for nanoelectronics. The injection of different types of impurities inside an alumina matrix can substantially improve its electrophysical properties. It is very important to study the local environment (chemical bonds, electronic structure, etc.) of injected atoms for understanding physical principles of the electronic elements formation. A number of techniques can be used to determine a chemical state of atoms in near surface layers. The most informative and precise technique is X-ray photoelectron spectroscopy. At the same time, Auger electron spectroscopy (AES) is also used for a chemical analysis [1] and can be even applicable for an analysis of dielectrics. The chemical state analysis of Ti and Cu atoms implanted into anodic aliunina films was carried out in this work by means of AES. 

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