Bulk bioactive ceramics

Relatively inert ceramics elicit minimal tissue response and lead to a thin layer of fibrous tissue immediately adjacent to the surface. Surface-active ceramics are partially soluble, resulting in ion-exchange and the potential to lead to a direct chemical bond with bone. Bulk bioactive ceramics are fiilly resorbable, have much greater solubility fiian surface-active ceramics, and may ultimately be replaced by an equivalent volume of regenerated tissue. The relative level of bioactivity mediates the thickness of Ae interfacial zone between the biomaterial surface and host tissue (Fig. 13.1). There are, however, no standardized measures of reactivity, but the most common are pH changes, ion solubility, tissue reaction, and any number of assays that assess some parameter of cell function. 

If a nearly inert material is implanted into the body it initiates a protective response that leads to encapsulation by a nonadherent fibrous coating about 1 i.m thick. Over time this leads to complete isolation of the implant. A similar response occurs when metals and polymers are implanted. In the case of bioactive ceramics a bond forms across the implant-tissue interface that mimics the bodies natural repair process. Bioactive ceramics such as HA can be used in bulk form or as part of a composite or as a coating. Resorbable bioceramics, such as tricalcium phosphate (TCP), actually dissolve in the body and are replaced by the surrounding tissue. It is an important requirement, of course, that the... 

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