Probing the surface structure of hydroxyapatite through its interaction with hydroxyl: a first-principles study.

Area of Science:

• Biomaterials Science
• Surface Chemistry
• Computational Materials Science

Background:

• Hydroxyapatite (HAp) is a critical biomaterial, but its surface interactions in physiological environments are not fully understood.
• Hydroxyl ions play a significant role in the HAp surface chemistry and its biological interactions.
• Accurate surface models are essential for predicting HAp behavior in biomedical applications.

Purpose of the Study:

• To investigate the interaction patterns between hydroxyl and different hydroxyapatite (HAp) facets.
• To determine the energetic favorability of hydroxyl adsorption on various HAp surfaces.
• To compare the suitability of hydroxyl-coated versus Ca-terminated surface models for HAp.

Main Methods:

• Periodical density functional theory (DFT) calculations were employed.
• The (100), (010), and (001) facets of HAp were studied.
• Comparative analysis of Ca-rich, PO4-rich, and mixed Ca-PO4-OH surfaces was performed.

Main Results:

• The formation of CaOH was energetically favored on the (100) and (001) facets, while Ca(OH)2 formation was favored on the (010) facet.
• Ca-OH interactions were found to be energetically stronger than Ca-water interactions.
• The influence of Ca-O bonding on OH stretching vibrations was analyzed.

Conclusions:

• Hydroxyl adsorption significantly modifies HAp surface properties.
• Hydroxyl-coated surface models provide a more accurate representation of HAp in physiological environments.
• This research refines surface models for HAp-based biomaterials, improving predictions of their activity and performance.