Ceramics may call to mind such objects as teapots and tile floors. There are many applications of technical interest, however, including such wide-ranging uses as supports for electronic devices and catalysts, separation membranes, cutting tools, components for use in high temperature corrosive environments such as engines, and, increasingly, biomedical applications.
Bioceramics can have structural functions as joint or tissue replacements, can be used as coatings to improve the biocompatibility of metal implants, and can function as resorbable lattices which provide temporary structures and a framework that is dissolved, replaced as the body rebuilds tissue. Some ceramics even feature drug-delivery capability.
Materials for surgical implants and medical devices must, before all else, be non-toxic. Bioceramics meet that test, and can be, in addition
- Bioinert, that is, not interactive with biological systems,
- Bioactive, durable materials that can undergo interfacial interactions with surrounding tissues,
- Biodegradable, soluble or resorbable (eventually replaced or incorporated into tissue).
The perfect material for medical applications would not only be biocompatible, but also have physical properties similar to those of the tissue being replaced or repaired. Ceramics, though they include good chemical and corrosion-resistant properties, are notoriously brittle. Researchers therefore have sought ways of combining desirable ceramics with other materials to tailor properties such as strength and elasticity to meet system requirements. Composites, functionally gradient materials, and coatings have been studied to optimize material choices.
Much work has been devoted to the interfacial reactions of biological systems with hydroxyapatite, a ceramic with chemical structure very similar to the hard structure of bone. Hydroxyapatite is used as a coating for metal surgical implants (most often made of titanium and its alloys, or stainless steels), and recent studies have examined the possibility of its use in composite form, in materials that combine polymers with ceramic or metal/ceramic combinations. Considerable research has been performed on methods of coating application and in-situ synthesis of apatites, and the implications for ceramic properties and microstructure.
Ceramics in a number of forms and compositions are currently in use or under consideration, with more in development. Alumina and zirconia are among the bioinert ceramics used for prosthetic devices. Bioactive glasses and machinable glass-ceramics are available under a number of trade names. Porous ceramics such as calcium phosphate-based materials are used for filling bone defects. The ability to control porosity and solubility of some ceramic materials offers the possibility of use as drug delivery systems. Glass microspheres have been employed as delivery systems for radioactive therapeutic agents, for example.
Material selection must also include consideration of the ease of forming into sometimes complex shapes, and with strict dimensional tolerances. Devices for use within the body must be able to withstand corrosion in a biological environment and endure use for years without undue wear (and without causing damage to surrounding tissues). Before insertion, they should be unchanged during storage, and must be sterilized without damage.
Materials scientists must keep in mind a multitude of properties and capabilities as they seek to develop the materials that will serve to improve the lives of patients.
The thermal and chemical stability of ceramics, high strength, wear resistance and durability all contribute to making ceramics good candidate materials for surgical implants.
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- CSA Ohio Office Assistant Manager
- Editor, Ceramics Abstracts, Engineered Materials Abstracts, and Metals Abstracts; additional duties relating to Materials Information files
- M.S. Chemistry, University of Pennsylvania, Philadelphia, PA
- B.A. Chemistry (magna cum laude), Dominican University, River Forest, IL