Papers by Author: Dmitrijs Jakovlevs

Abstract: The objective of this work is to synthesize pure and Mg-substituted hydroxyapatite (HAp) powders with different MgO content in synthesis media (in the wide range of 0.1-10.0 wt% in respect to Ca), and to study the influence of Mg²⁺ ions substitution on the physicochemical properties of HAp materials. In this work HAp and magnesium-substituted hydroxyapatite (Mg-HAp) were synthesized by modified wet chemical precipitation of homogenous suspension of Mg(OH)₂/Ca(OH)₂ and H₃PO₄ solution. Systematic investigation on as-synthesized and sintered Mg-HAp and HAp samples shows that the incorporation of MgO promotes decomposition of HAp to β-tricalcium phosphate (β-TCP) and significantly modified its microstructure. The effect and evidence of incorporation of Mg²⁺ ions into HAp structure is discussed.

Abstract: Modification of surface morphology and composition of niobophosphate glass and glass-ceramic in the system P₂O₅-CaO-Nb₂O₅-Na₂O was investigated. Amorphous, partly crystalline and crystalline samples were prepared in shape of pellet with diameter 10 mm. Samples were treated in 1 and 5 days in citric acid at 37°C and 3h in boiling HCl. Surface morphology before and after treatment was investigated by scanning electron microscopy (SEM), phase composition by X-ray powder diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX). Glass sample was smooth, after treatment in citric acid it had cracks and pit-holes on the surface. Partly crystalline sample was smooth and contained inclusions of crystalline Ca₃(PO₄)₂ and Ca₂P₂O₇. Platy crystals of Ca₃(PO₄)₂ dissolved first, than bulky Ca₂P₂O₇. Crystalline samples contained Na₄Nb₈P₄O₃₂ and calcium phosphate phases; surface was rough before and after treatment. EDX showed that amount of phosphorous is proportional to amount of calcium and inversely proportional to amount of sodium and niobium in glass-ceramic samples.

Abstract: In this work three different preparation techniques of biphasic calcium phosphate (BCP) bioceramics (consisting of both hydroxyapatite (HAp) and β-tricalcium phosphate (TCP)) are compared: sintering of synthetic calcium-deficient apatites (CDAs) (intimate mixture of HAp and TCP - SBCP), sintering of mechanical mixture of synthetic HAp and apatitic tricalcium phosphate (Ap-TCP) - MBCP and sintering of mechanical mixture of synthetic HAp and calcium metaphosphate glass (CMG) - GBCP. Two different HAp/TCP phase ratios were investigated: 20/80 and 60/40. Phase composition, microstructure, sintering properties and microporosity of obtained BCP bioceramics were investigated. The open porosity of prepared BCP bioceramics is strongly influenced by phase composition and preparation technique. BCP bioceramics SBCP and MBCP have homogeneous microstructure, whereas GBCP has inhomogeneous inclusions of dense TCP. High content of hydroxyapatite (HAp) phase in MBCP and SBCP correlates with high microporosity.