Molecular Dynamics Exploration of Ordered-to-Disordered Surface Structures of Biomimetic Hydroxyapatite Nanoparticles

CQ Xie and ZY Xue and HJ Gu and CF Hu and ML Yang and X Wang and DG Xu, JOURNAL OF PHYSICAL CHEMISTRY C, 122, 6691-6703 (2018).

DOI: 10.1021/acs.jpcc.8b00178

Hydroxyapatite (HAP, Ca-10(PO4)(6)(OH)(2)) constitutes one of the main components in human bones and teeth. Investigations of the surface structures of HAP could help us to understand the interactions between the implant HAP-based biomaterials and their environment. We, in this work, systematically explored the surface structures of HAP based on two different force fields, Born-Mayer-Huggins (BMH) parameters and interface force fields (IFFs). Their different performances in constructing HAP ordered-to-disordered surface structures were compared and discussed. The annealed HAP (001), (010), (100), and (110) surface structures were obtained, and their thickness values of the disordered layers have been computed. The thicknesses have the same order of (001) < (010) < (100) < (110) even at different annealing temperatures by the two force fields. At the annealing temperature 1800 K, the theoretical prediction for the average disordered layer thickness values is 8.9 angstrom (BMH) and 10.3 angstrom (IFF), which are close to the experimental measurement of 10-20 angstrom. Further studies on the surface models of (010) and (100) with different ion-rich terminations show that the disordered layer thickness of the P-rich surface are systematically larger than that of the Ca-rich surfaces. In the surface structure analyses, total pair distribution functions, static structure factors, and the coordination numbers for Ca or P were performed. These analyses show that our present HAP surface models have obvious ordered- to-disordered topology. In the present molecular dynamics exploration on the surface structures of HAP, several new surface models with different terminations for HAP-based biomaterials have been suggested, which may be appropriate for further investigation of interactions between biomolecules and HAP material.

Return to Publications page