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Hydroxyapatite: Mechanism of formation and properties

Hydroxyapatite: Mechanism of formation and properties Hydroxyapatite (HA) was prepared by stirring amorphous calcium phosphate (ACP), which contained occluded Cl− as a tracer ion, in distilled water buffered to pH 7.4 by tris-HCl at 25, 37, 60, 80 and 100°. HA made in this manner contained from less than 1% (25°) to 11% (100°) of the amount originally occluded in the precursor ACP. These results suggest that the principal mechanism of conversion is a series of solution- mediated rate processes that enable ions to move away from the dissolving ACP before the onset of HA nucleation.In situ ACP rearrangement does not provide for ion escape and is probably not involved in the conversion. The infrared spectra of high specific surface HA prepared at 25° and 37° showed no OH stretching or OH librational bands, while the lower specific surface HA (60°, 80°, 100°) displayed sharp bands of these vibrational modes. This effect is attributed to hydrogen bonding of structural OH groups on the surface on HA crystals with the strongly adsorbed water monolayer present on HA. As in other systems, hydrogen bond formation probably smears out the OH absorption bands so that only OH groups in the crystal interior yield sharp, unperturbed OH bands. As the HA specific surface decreases, the smearing effect becomes minimal due to a concomitant decrease in the percentage of surface-located OH groups. This may explain the observed absence of OH vibrational modes in the infrared spectrum of bone mineral, since bone apatite has a specific surface comparable to that of HA synthesized at 25° and 37°. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Calcified Tissue International Springer Journals

Hydroxyapatite: Mechanism of formation and properties

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References (25)

Publisher
Springer Journals
Copyright
Copyright © 1973 by Springer-Verlag
Subject
Life Sciences; Biochemistry, general; Endocrinology; Orthopedics; Cell Biology
ISSN
0171-967X
eISSN
1432-0827
DOI
10.1007/BF02015413
Publisher site
See Article on Publisher Site

Abstract

Hydroxyapatite (HA) was prepared by stirring amorphous calcium phosphate (ACP), which contained occluded Cl− as a tracer ion, in distilled water buffered to pH 7.4 by tris-HCl at 25, 37, 60, 80 and 100°. HA made in this manner contained from less than 1% (25°) to 11% (100°) of the amount originally occluded in the precursor ACP. These results suggest that the principal mechanism of conversion is a series of solution- mediated rate processes that enable ions to move away from the dissolving ACP before the onset of HA nucleation.In situ ACP rearrangement does not provide for ion escape and is probably not involved in the conversion. The infrared spectra of high specific surface HA prepared at 25° and 37° showed no OH stretching or OH librational bands, while the lower specific surface HA (60°, 80°, 100°) displayed sharp bands of these vibrational modes. This effect is attributed to hydrogen bonding of structural OH groups on the surface on HA crystals with the strongly adsorbed water monolayer present on HA. As in other systems, hydrogen bond formation probably smears out the OH absorption bands so that only OH groups in the crystal interior yield sharp, unperturbed OH bands. As the HA specific surface decreases, the smearing effect becomes minimal due to a concomitant decrease in the percentage of surface-located OH groups. This may explain the observed absence of OH vibrational modes in the infrared spectrum of bone mineral, since bone apatite has a specific surface comparable to that of HA synthesized at 25° and 37°.

Journal

Calcified Tissue International – Springer Journals

Published: Jul 14, 2005

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