Bioinert ceramics

As discussed in Section 10.2, bioinert materials do not release any toxic constituents, but neither do they show any positive interaction with living tissue. As a response of the body to these materials, a nonadherent capsule of connective tissue is usually formed around the bioinert material that, in the case of bone remodeling, manifests itself by a shape-mediated contact osteogenesis. Hence, only compressive forces will be transmitted through the bone-material interface ( bony on-growth ). 

Extremely pure, fine-grained alumina polycrystals have been used for about 35 years for the femoral heads of hip endoprostheses (Boutin, 1972, 1981). Today, there exists a large variety of chnical options to combine femoral heads and acetabular cups. In Germany, these medical products are marketed under the brandname BIOLOX and BIOLOX forte by CeramTec AG (formerly Feld-miihle) (Clarke and WiUmann, 1994 Willmann, 2002). In 2000, the German market volume of ceramic femoral heads amounted to about DM 30 million this corresponded to 90000 units, 90% of which were made from alumina. 

This latest trend in load-bearing materials for arthroplastic applications involves the development of highly fracture-resistant alumina/zirconia composites, as an alternative choice to alumina and zirconia monolithic ceramics. Composite materials are designed from both chemical and microstructural viewpoints in order to prevent environmental degradation and fracture events in vivo. Based on the experimental determination of an activation energy value for an environmentally driven tetragonal to monoclinic transformation, the long-term in vivo environmental resistance of prostheses made from these composite materials can be predicted (Chevalier et al., 2009). 

For about 40 years, chemically very pure, extremely fine-grained polycrystalline alumina ceramics have been used to fashion femoral heads of hip endoprostheses (Boutin, 1972,1981). 

Bioceramic Coatings for Medical Implants Trends and Techniques, First Edition. 

In the past, some concern has been voiced that long-term alumina-bearing implants could lead to elevated concentration of aluminium in the body (Lewandowska-Szumiel and Komender, 1990). Such enhanced aluminium levels are considered to be an aetiological agent in dialysis osteomalacia, encephalopathy and some forms of anaemia (Alfrey, 1984 Parkinson, Ward and Kerr, 1981). However, since to date there are no clinical reports on the upper safety levels of aluminium in human bone the effect of even minute quantities of aluminium released from alumina femoral heads needs further investigation. 

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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... 

In this chapter, we will attempt to trace briefly the long and sometimes anfractuous history of important bioceramics including coatings. Emphasis will be put on the bioinert ceramics alumina and zirconia, as well as on bioactive, that is osseo-conductive calcium phosphates. 

Femoral ball heads of hip endoprostheses made from bioinert ceramics such as alumina or zirconia have to sustain high mechanical stresses, resorp-tion/corrosion by aggressive body fluid and abrasive wear over the lifetime of the implant in the human body of 15-20years. Some important properties of ceramic femoral ball heads are listed in Table 2.3 (Willmann, 1995). Mechanical properties of alumina and zirconia are discussed in Chapter 4.1. 

In contrast to bioinert ceramics osseoconductive ceramics show a positive interaction with living tissue including chemical bonding to the bone along the... 

A limited number of contributions dealing with HVSF-sprayed alumina coatings exist. While these contributions appear to have no direct bearing to bioceramic coatings, alumina is considered a bioinert ceramic and, in the future, applications may arise for such coatings in the biomedical realm. 

Nonabsorbable or Relatively Bioinert Bioceramics. 39-2 Relatively Bioinert Ceramics Alumina (AI2O3) Zirconia (Zr02) Carbons... 

Relatively bioinert ceramics maintain their physical and mechanical properties while in the host. They resist corrosion and wear and have aU the properties listed for bioceramics in Table 39.1. Examples of relatively bioinert ceramics are dense and porous aluminum oxides, zirconia ceramics, and single phase calcium aluminates (Table 39.2). Relatively bioinert ceramics are typically used as structural-support... 

Bioceramics Bioinert ceramics Bioinert (is not rejected), biocompatible Replacement/repair of teeth, coatings, root pins, crowns... 

A strong interest in the use of ceramics for biomedical engineering applications developed in the late 1960 s. Used initially as alternatives to metallic materials in order to increase the biocompatibility of implants, bioceramics have become a diverse class of biomaterials presently including three basic types relatively bioinert ceramics maintain their physical and mechanical properties in the host and form a fibrous tissue of variable thickness surface reactive bioceramics which form a direct chemical bonds with the host and bioresorbable ceramics that are dissolved with the time and the surrounding tissue replaces it. 

Bioinert Relatively bioinert ceramics maintain their physical and mechanical properties while in the host. They are those stable bioceramics that do not react appreciably when they are implanted in the body. The implant does not form a bond with bone. Alumina (a-Al203) is a typical example of ceramic bioinert. Other examples, as we see next, are the zirconia ceramics (Zr02) and pirolitics carbon ceramics. 

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