An experimental-computer modeling study of inorganic phosphates surface adsorption on hydroxyapatite particles

Area of Science:

• Materials Science
• Surface Chemistry
• Computational Chemistry

Background:

• Hydroxyapatite (HAp) is a key biomaterial, and understanding its surface interactions with phosphate species is crucial for applications in bone regeneration and biomaterials.
• Phosphate-based compounds are relevant in biological systems and industrial processes, necessitating detailed studies of their adsorption behavior on mineral surfaces.

Purpose of the Study:

• To investigate the adsorption mechanisms of orthophosphate, pyrophosphate, triphosphate, and trisphosphonate on hydroxyapatite surfaces.
• To compare experimental spectroscopic data with quantum mechanical calculations to elucidate adsorption preferences and energetics.
• To understand the influence of HAp surface crystallography and phosphate structure on adsorption.

Main Methods:

• Experimental adsorption studies using Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS).
• Preparation and characterization of crystalline HAp and amorphous calcium phosphate particles.
• Density functional theory (DFT) calculations on HAp (100) and (001) surfaces using slab models.

Main Results:

• Phosphate adsorption is energetically favored on both HAp surfaces, consistent with HAp growth mechanisms.
• Triphosphate adsorption is easier than pyrophosphate adsorption due to its flexibility, overcoming electrostatic limitations.
• Trisphosphonate is predicted to adsorb exclusively on the HAp (001) surface.
• Experimental results align with DFT predictions, indicating that prepared HAp particles predominantly expose the (100) surface.

Conclusions:

• The study provides a comprehensive understanding of phosphate species adsorption on HAp, integrating experimental and theoretical approaches.
• The findings highlight the importance of surface geometry and molecular flexibility in determining adsorption behavior.
• Experimental conditions favoring the (100) HAp surface explain the observed adsorption patterns for pyrophosphate, triphosphate, and trisphosphonate.