ABSTRACT
Despite recent advances in our knowledge of the chemistry, structure and short range order of the calcium-phosphate crystals of apatite in the mineralized tissues of vertebrates, there still remain a number of critical important characteristics which need to be explored, not only for the sake of a clearer understanding of the intimate nature of the inorganic crystals per se, but also to help elucidate the biological functions of the crystals. These commonly accepted functions have now been extended to include mineral-cell interactions, either directly or via the binding of specific protein components through the mineral crystallites and the interaction of such mineral-bound proteins with the surrounding cells; for example, the role of mineral-bound osteocalcin in recruiting and facilitating differentiation of mononuclear cells to osteoclasts and their participation in bone resorption. 1 Further progress especially in the elucidation of the fine structure and short range order of the bone crystals has been seriously limited, however, by the fact that the inorganic crystals are anatomically intimately related at the ultrastructural level to the major organic constituents of the extracellular matrix, viz., their location within the collagen fibrils of bone, dentin, cementum, and within the protein rich “tubules” of enamel. 2 Moreover, it is very likely that there are strong chemical bonds formed between the mineral crystallites, collagen and other protein components of the organic matrix, as well. The organization at the ultrastructural level of the major organic matrix components and the inorganic crystals, not only prevents a direct visualization of individual crystals necessary to determine the size and shape of the crystals and any changes in these parameters with maturation and aging, for example, but seriously interferes with techniques such as Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) used to explore the fine, short range order of the crystals. The purpose of this research progress was to develop methods to isolate the crystals of bone and other mineralized tissues essentially free of organic constituents without altering the 332chemical composition or structure of the crystals, and to disperse the crystals so that they can be examined visually by high resolution transmission electron microscopy and by electron diffraction and microprobe analyses.
