Ultrastructure of the Mineralized Tissue/Calcium Phosphate Interface in Vitro

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Abstract
An in vitro rat bone marrow cell (RBMC) system was used to examine the structure of the interface established between calcium phosphates (Ca-P) and mineralized tissue. The Ca-P used, varied either in chemical structure or crystallinity. Therefore, not only the influence of chemical composition, but also the effect of degradation of Ca-P ceramics could be studied. The interfaces were examined with scanning and transmission electron microscopy (SEM and TEM).SEM showed that deposition of mineralized extracellular matrix on the different materials examined varied both in time and morphology. Mineralization started with the formation of afibrillar globules with which collagen fibres became integrated. With TEM, three distinctly different interfacial structural arrangements were observed which were dependent on the presence or absence of an electron dense layer and/or an amorphous zone. The former was considered to be at least partially caused by protein adsorption, which would precede biological mineralization events, whereas the latter was considered to represent partial degradation of the ceramic surfaces.The results of this study showed that interfacial reactions were not only influenced by the chemical structure, but also by the crystallinity of Ca-P ceramics. Thus, characterisation of Ca-P implant materials is of critical importance in achieving a better understanding of the phenomena that occur at the bone-biomaterial interface.