Journal of Dental Research, Vol 63, 1348-1354, Copyright © 1984 by International & American Associations for Dental Research Online Journals
High-resolution electron microscopy of hydroxyapatite grown in dilute solutions
T. Aoba, C. Yoshioka, T. Yagi and E. C. Moreno
High-resolution electron microscopy (HREM) was applied to the study of
seeded crystal growth of hydroxyapatite (HA) in supersaturated solutions.
The HA seed crystals were rod-shaped, elongated along the c-axis, and
showed smooth contours. The seed crystals exhibited hexagonal prism facets,
and one end was rhombohedrally terminated, whereas the opposite end was
blunt. Growth experiments were carried out at 37 degrees C, and solution
compositions were carefully selected to avoid the involvement of precursor
phases during the HA growth. After five-hour growth, the total amount of
precipitation was from 3 to 7% of the initial crystal mass added to the
solutions; examination of the crystals by HREM disclosed the formation of
projections on the end surfaces of the HA crystals. High-resolution TEM
clearly showed lattice fringes with predictable spacings over the entire
crystal specimen, including the formed projections. Analysis of selected
regions by optical diffraction of the HRTEM fringe negatives showed that
the nature and orientation of the projections were similar to those of the
underlying seed crystal. High-resolution SEM of the HA crystal after
five-hour growth disclosed step-like structures on the prism faces, as well
as the projections localized on the ends. These results strongly suggest
that more than one growth process may be involved, perhaps related to the
distinct faces of the HA seed crystals.
