Ceramics and glasses

Ceramics are renowned for their excellent wear properties, good resistance to degradation in corrosive environments, high modulus and hardness values and high melting points. Equally well known are their poor thermal and electrical conductivities and their reputation for being notch sensitive with low values of fracture toughness. Historically, as a consequence of low impact and tensile strengths combined with inherent brittleness, their use was limited. However, more recently, advances in manufacturing technology have meant that a group of what can be termed high performance engineering ceramics have emerged that can be used for a wide range of applications. Their high melting point has led to their use in engines and turbines at elevated temperatures. As a consequence of their improved toughness, they have been incorporated in the design of body armour. Their excellent wear resistance, high compressive strength properties, pleasing aesthetic appearance and proven biocompatibility have led to the development of a specific range of what are referred to bioceramics which are now used extensively in many different areas of medicine to augment or replace parts of the body. Alumina and zirconia are used to manufacture components of hip joint replacements; hydroxyapatite (HA) and glass ceramics are used as coatings on prosthetic stems; calcium phosphate based materials are used as porous scaffolds, spinal implants and bone grafts; composites of HA combined with a polymer are used to manufacture replacements for the bones of the inner ear – these are only a few examples of the wide range of applications of ceramics in medical engineering.