Biocompatibility of hydroxyapatite ceramic: response of chondrocytes in a test system using low temperature scanning electron microscopy.

An investigation is described of R37W, one of a number of porous ceramics being developed for maxillofacial surgery and the restoration of periodontal bone defects. Sensitive and precise methods are needed to assess the biocompatibility of these new materials. Mammalian chondrocytes are known to form colonies on and within porous ceramics; therefore, the tissue formed has been evaluated to gauge the response of these proliferating mesenchymal cells to the hydroxyapatite. Cell colonies, grown on R37W, have been rapidly frozen at -210 degrees C (63K) in nitrogen slush and examined by low temperature scanning electron microscopy (SEM). This method enables unfixed, fully hydrated cells to be viewed in detail and demonstrates the three-dimensional surface structure of chondrocytes in a life-like state. Features such as complex pericellular fenestrations and papilliform surface processes are believed to indicate cell viability and normality: they are not detectable by the light microscopy and SEM of fixed, dehydrated preparations. This recently recognized fine structure, together with the determination of rates of increase of cell numbers and histochemical and immunological tests of cell synthetic and secretory behaviour, provides a new guide to biocompatibility. It is concluded that the low temperature SEM of chondrocytes grown on ceramics is a valuable addition to the procedures available for the testing of hard materials before their adoption in oral surgery.