Computational study of hydroxyapatite structures, properties and defects

Компьютерные Исследования Наноструктур Гидроксиапатита, Их Особенности И Свойства

“…Naturally, HAP is a mineral form of calcium apatite with the formula Ca5(PO4)3(OH), but it is often written as Ca10(PO4)6(OH)2 to denote that the crystal unit cell comprises two molecular units. The specific feature of HAP is that the OH − ions form inner channels along the c axis with various random OH-dipoles orientations under different external conditions, which allow the transfer of protons along this axis under special conditions (such as temperature heating and applied electric field with necessary critical values) [28][29][30][31][32]35]. Usually HAP has 2 main different forms of nano-crystalline structures (in hexagonal P63/m and monoclinic P21/b space group structures) and amorphous structure.…”

“…Both the phases are periodically repeated in space and form an ideal crystallographic structure for the whole of the crystal with exact positions for each atom. It is important to note that for such ideal crystallographic structures the relation of atoms Ca and P must correspond strictly to the correct stoichiometry, with a ratio of Ca/P of 1.67 [1,5,35]. In a real mineral there could be many deviations from such ideal structures, including such defects as various vacancies, interstitials and replacements of several atoms [32,35].…”

“…It is also useful for creating of new HAP nanostructures having wide biomedical applications [13][14][15][16][17][18][19]. The results of these studies [7,9,11,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] allow us to clarify possible mechanisms of structural changes and electrical properties of HAP in the bulk crystal and on the crystal surface (electrical potential, charges and polarization). And this, in turn, will allow one to improve the efficiency of HAP interactions with the living bone cells (osteoblasts, osteoclasts, etc.)…”

“…Studies have shown that the creation of such surface charges (or HAP polarization) increases the adhesion of the osteoblasts cells and enhances their reproduction and growth. According to [34][35][36][37][38], it is especially noticeable for the negatively charged surfaces of HAP.…”

“…Beyond HAP crystal bulk model, a special HAP model of the layered slab supercells units, which includes vacuum spaces between the layered slabs forming HAP surface, are considered and analysed too [5]. More computational details are described in [22,24,26,27,[30][31][32][33][34][35]67] and in sections below.…”