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Updated: Jan 2, 2026
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Rapid Mix Preparation of Bioinspired Nanoscale Hydroxyapatite for Biomedical Applications
Published on: February 23, 2017
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Preparation and Solubility of Hydroxyapatite.
E C Moreno1, T M Gregory1, W E Brown1
1Institute for Basic Standards, National Bureau of Standards, Washington, D.C. 20234.
Summary
Heating synthetic hydroxyapatite (HA) in air or steam affects its solubility. Air-heated HA exhibits higher solubility, impacting its behavior in aqueous systems and potential applications.
Area of Science:
- Materials Science
- Geochemistry
- Biomineralization
Background:
- Hydroxyapatite (HA), Ca5OH(PO4)3, is a key biomaterial and mineral.
- Understanding HA solubility is crucial for applications in bone regeneration, dental materials, and environmental science.
- Thermal treatment can alter HA's physical and chemical properties, influencing its dissolution behavior.
Purpose of the Study:
- To investigate the effect of air and steam heating at 1,000 °C on the solubility of synthetic hydroxyapatite.
- To determine the solubility isotherms and activity products of HA samples treated under different atmospheres.
- To analyze the implications of altered solubility on the precipitation of HA and related calcium phosphates.
Main Methods:
- Synthesis and full characterization of synthetic hydroxyapatite (HA) using x-ray, infrared, petrographic, and chemical analyses.
- Heating HA samples at 1,000 °C in air and steam atmospheres.
- Determination of solubility isotherms in the Ca(OH)2-H3PO4-H2O system (pH 5-7) by equilibrating solids with dilute phosphoric acid solutions.
- Calculation of activity products using least squares adjustment, considering electroneutrality, constant activity product, and stoichiometric dissolution, with allowance for ion pairs [CaHPO4]0 and [CaH2PO4]+.
Main Results:
- Both air- and steam-heated HA samples dissolved stoichiometrically.
- The activity product for steam-heated HA was 3.73 ± 0.5 × 10^-58, while for air-heated HA it was 2.51 ± 0.4 × 10^-55.
- Air-heated HA exhibited significantly higher solubility compared to steam-heated HA.
- The singular points of HA solubility isotherms with brushite (CaHPO4·2H2O) and dicalcium phosphate (CaHPO4) occurred at a pH one unit higher for air-heated HA.
Conclusions:
- Thermal treatment atmosphere (air vs. steam) critically influences hydroxyapatite solubility.
- The increased solubility of air-heated HA is attributed to potential changes in heat of formation (partial dehydration) or fine subdivision (disproportionation).
- These findings provide insights into the conditions governing HA precipitation and dissolution, relevant for biomaterial design and geochemical processes.
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