First-Principles Study of Structure, Vibrational, and Elastic Properties of Stoichiometric and Calcium-Deficient Hydroxyapatite

Abstract

Hydroxyapatite (HAp), a primary constituent of human bone, is usually nonstoichiometric with varying Ca/P molar ratios, with the well-known fact that Ca deficiency can cause marked reductions in its mechanical properties. To gain insights into the mechanism of this degradation, we employ first-principles calculations based on density functional theory and determine the effects of Ca deficiency on structure, vibrational, and elastic properties of HAp. Our simulation results confirm a considerable reduction in the elastic constants of HAp due to Ca deficiency, which was experimentally reported earlier. Stress-induced transformation of the Cadeficient defected structure into a metastable state upon the application of stress could be a reason for this. Local structural stability of HAp and Ca-deficient HAp structures is assessed with full phonon dispersion studies. Further, specific signatures in the computed vibrational spectra for Ca deficiency in HAp can be utilized in experimental characterization of different types of defected HAp.

Physical and biological characteristics of nanohydroxyapatite and bioactive glasses used for bone tissue engineering

“…It should be mentioned that calcium phosphate compounds with Ca/P ratio of < 1:1 are not suitable for Reprinted with permission from Ref. [12]. Copyright © 2014 American Chemical Society.…”

“…The study included needle-shaped (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) , the stronger the toxicity (Figure 8) [80]. Most of the cytotoxicity was attributed to apoptosis rather than necrosis.…”

Second‐order elastic constants of hexagonal hydroxylapatite (P63) fromab initioquantum mechanics: Comparison between DFT functionals and basis sets

“…Albeit the unit cell parameters and internal geometry of hydroxylapatite were systematically described in previous theoretical works, here we present a detailed comparison between the results obtained by different quantum mechanical approaches. It is well‐known that many bulk properties, such as the SOECs or vibrational spectra, strongly depends on the geometry of the unit cell, which in turn depends on the computational framework employed.…”

“…These results could be also of much help for experimental researcher interested in the mechanical properties of OHAp. There are some theoretical work in literature that report this physical quantity related to hydroxylapatite, but it was obtained only by plane wave basis sets and without any treatment of van der Waals interactions. Here, we intended to extend the knowledge about the SOECs including data calculated using by GTO.…”

Estudo, caracterização e propriedades de ortofosfatos multifuncionais

“…Ou seja, com os processos de difusão de matéria, a diferença entre o comprimento e a largura das partículas diminui, evidenciando uma preferência da densificação nos planos {100}. [86,87,197,201,203], além do modelo de banda larga [121]. A estrutura eletrônica da HA perfeita e sem defeitos é constituída por níveis de energia provenientes dos clusters de [PO4] (banda de valência) e Ca (banda de condução) e com energia de gap similar aos apontados para amostras com caráter isolante.…”