Increasing A-type CO₃²⁻ Substitution Decreases the Modulus of Apatite Nanocrystals

Authors

Stephanie Wong, Oak Ridge National Laboratory
Abigail Eaton, University of Arkansas, Fayetteville
Christina Krywka, CIRIMAT, University of Toulouse
Arun Nair, Air Force Institute of TechnologyFollow
Christophe Drouet
Alix Deymier, University of Connecticut Health Center, Farmington

Document Type

Article

Publication Date

3-1-2025

Abstract

Biological apatite mineral is highly substituted with carbonate (CO₃²⁻). CO₃²⁻ can exchange for either phosphate, known as B-type, or hydroxyl groups, known as A-type. Although the former has been extensively studied, A-type CO₃²⁻ substituted apatites are poorly understood. Therefore, A-type CO₃²⁻ apatites with biologically relevant levels of CO32− (1.7–5.8 wt%) were prepared and characterized. The addition of A-type CO₃²⁻ into the apatite structure caused the predicted expansion of the a-axis and contraction of the c-axis in the unit cell. This was accompanied by a significant modification in the atomic order, especially along the a-axis plane, and crystallite size. A combination of in situ loading with synchrotron X-ray Diffraction and Density Functional Theory showed that increasing A-type CO₃²⁻ substitutions also reduced the bulk and elastic moduli of the crystals. These results show that although A-type CO₃²⁻ may inhibit lattice changes caused by B-type CO32−, A-type CO₃²⁻ enhances the reduction in crystal order and mineral stiffness. These results help us to identify the possible contributions of A-type CO₃²⁻ substitutions in biological apatites that contain both A- and B-type CO₃²⁻. In addition, this implies that the stiffness of bioapatite may change with increasing A-type CO₃²⁻ substitutions, potentially altering the fracture mechanics of calcified tissues and biomaterials.

Comments

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Plain-text title form: Increasing A-type CO32− substitution decreases the modulus of apatite nanocrystals

DOI

10.1016/j.jmbbm.2025.106962

Source Publication

Journal of the Mechanical Behavior of Biomedical Materials

Recommended Citation

Wong, S., Eaton, A., Krywka, C., Nair, A., Drouet, C., & Deymier, A. (2025). Increasing A-type CO32− substitution decreases the modulus of apatite nanocrystals. Journal of the Mechanical Behavior of Biomedical Materials, 166, 106962. https://doi.org/10.1016/j.jmbbm.2025.106962