High-resolution electron microscopy of hydroxyapatite grown in dilute solutions

Area of Science:

• Crystallography
• Materials Science
• Biomineralization

Background:

• Hydroxyapatite (HA) is a key biomineral in bone and teeth.
• Understanding HA crystal growth is crucial for biomaterial development.
• Seeded crystal growth offers insights into nucleation and propagation.

Purpose of the Study:

• To investigate the microstructural changes during seeded hydroxyapatite crystal growth.
• To characterize the morphology and crystallographic nature of newly formed HA structures.
• To elucidate the mechanisms governing HA crystal growth in supersaturated solutions.

Main Methods:

• High-resolution electron microscopy (HREM) for detailed imaging.
• Transmission electron microscopy (TEM) to visualize lattice fringes.
• Scanning electron microscopy (SEM) to observe surface morphology.
• Optical diffraction analysis of HRTEM images.

Main Results:

• HA seed crystals exhibited hexagonal prism facets and distinct terminations.
• Projections with similar crystallographic orientation to the seed were observed on crystal ends after 5-hour growth.
• Step-like structures were identified on prism faces.
• Lattice fringes were continuous across projections, indicating coherent growth.

Conclusions:

• Seeded hydroxyapatite crystal growth involves the formation of projections on crystal ends.
• Distinct growth processes may occur on different crystal faces (ends vs. prisms).
• The observed growth mechanisms are consistent with the underlying seed crystal structure.