ATOMIC-FORCE MICROSCOPIC DETERMINATION OF SUBSTRATE EFFECTS ON THE STRUCTURE OF DEPOSITED BIOMINERAL PHOSPHATES

Periodicity observed by atomic force microscopy on the surface of two biological crystals, hydroxyapatite (HA) and brushite (DCPD), has allo wed identification of crystal planes indicative of preferred orientati on on several substrates. From isolated HA crystal clusters, deposited on to a glass substrate, two crystal planes were identified. The [001 ] and [110] spacings of HA are in agreement with published values take n from crystallographic data. Measurements made on DCPD platelets, dep osited on to glass, yielded atomic spacings presumed to be those of th e [110] crystal plane. For both minerals, comparison of atomic-scale i maging showed differences between deposits on glass or freshly cleaved mica. Larger scale structure was also found to differ when the minera l deposits were compared on gold, glass and mica. A very ordered struc ture was found when HA was deposited on to a gold substrate that had b een modified with a monolayer of an alkane thiol. These observations s uggest that different substrates influence the final structure of the crystals as determined by atomic force microscopic surface characteriz ation.