324: Understanding hydroxyapatite at the atomic scale: Implications for biomaterial design

Abstract: Hydroxyapatite (HAp, Ca10(PO4)6(OH)2, the principal inorganic component of bone, has been used as a model for bio-inspired interfaces that dynamically adapt to their chemical environment, exhibiting spontaneous protonation, hydration-driven reconstruction, and facet-specific reorganization in response to pH and ionic composition. These adaptive surface behaviors are central to biomineralization, dissolution, and biointerface formation, yet the atomic-scale mechanisms governing them remain incompletely understood, limiting the rational design of biomaterials and bone-targeted drug delivery systems with controlled interfacial properties. Plane-wave density functional theory (DFT) calculations, implemented in Quantum Espresso, are applied here to investigate how chemical environment, hydration state, protonation, and carbonate substitution, govern the structural and electronic properties of stoichiometric HAp surfaces. Facet identity emerges as a critical design variable where the basal (001) surface undergoes molecular H2O adsorption, while the prismatic (010) surface drives spontaneous dissociation and reconstruction, demonstrating how surface topology encodes distinct adaptive responses to identical stimuli. Carbonate substitution (CO32- for PO43-) further introduces configurational flexibility and ion mobility within apatitic channels, modulating interfacial reactivity beyond what stoichiometric models predict. Surface and adsorption energies for H2O and biologically relevant anions (CO32-, HCO3-, HPO42-, H2PO4 -) are computed alongside electrostatic potential maps to elucidate how carbonate incorporation and Ca2+ vacancies enhance or attenuate binding at each facet. In this work, we employ a molecular-scale computational framework to further the understanding of atomic-level mechanisms underlying emergent, environment-dependent interfacial phenomena in bio-inspired apatitic systems.