N. A. Zakharov

Dielectric characteristics of biocompatible Ca10(PO4)6(OH)2 ceramics

The temperature dependence of the dielectric permittivity and losses of biocompatible Ca10(PO4)6(OH)2 ceramics were studied in a temperature range from 20 to 500°C. An approach to the interpretation of anomalies (bending points) observed in the dielectric characteristics of the ceramic samples is proposed, which takes into account features of the crystal structure of calcium hydroxyapatite and the defects formed in the course of thermal treatments.

Gelatin-containing calcium hydroxyapatites: Synthesis and physicochemical characterization

The CaCl2-(NH4-)2HPO4-NH3-H2O-gelatin system was studied at 25°C using the solubility (residual concentrations) method. Stoichiometric nanocrystalline (11–15.4 nm) gelatin-containing calcium hydroxyapatites (HAs) were found to form. They were characterized by chemical analysis, thermal analysis, Xray powder diffraction, and IR spectroscopy.

The effect of graphene oxide (GO) on biomineralization and solubility of calcium hydroxyapatite (HA)

Interaction between GO and the counterpart of the bone tissue, calcium hydroxyapatite Ca10(PO4)6(OH)2 (HA), is modeled in the course of synthesis of nanosize composite materials (CMs) based on graphene oxide (GO) and biocompatible HA with a GO content of 0.1, 1.0, 2.0, and 5.0 wt % GO from aqueous solutions in the system of Ca(OH)2–H3PO4–GO–H2O under native conditions (37°C). The effect of CM composition on the size and morphology of HA nanocrystals (HA NCs) is determined using the methods of physico-chemical analysis (chemical, XRD, IRS, DTA, TDG, SEM, TEM). The solubility of HA NC CMs by Ca2+ ions in distilled water is determined under in vitro conditions, and the possible results of interaction between GO and native calcified tissues are analyzed.

The effect of carbon nanotubes on biomineralization and solubility of calcium hydroxyapatite Ca10(PO4)6(OH)2

Toxic characteristics of carbon nanotubes (CNTs) were estimated through the modeling of interaction between CNTs and the inorganic component of osseous tissue of mammals—calcium hydroxyapatite Ca10(PO4)6(OH)2 (HA)—under the conditions of biomimetic formation of HA/CNT composites containing 0.1, 1, and 5 wt % CNT. Synthesis products were identified using the methods of chemical analysis, XRD, DTG, DTA, IRS, SEM, TEM, and DE. The effect of nanotubes on crystallographic and morphological characteristics of nanocrystalline HA and solubility of HA/CNT composites was determined.

Synthesis and physicochemical characterization of nanocrystalline chitosan-containing calcium carbonate apatites

The CaCl2-(NH4)2HPO4-NH4HCO3-(C6H11NO4)n-H2O system at 25°C has been investigated by the solubility (Tananaev’s residual concentration) method and pH measurements. Coprecipitation conditions have been determined for nanocrystalline type A and B calcium carbonate apatites. Type A: Ca10(PO4)6(CO3)x(OH)2 − 2x · yC6H11NO4 · zH2O (x = 0.2, 0.5, 1.0; y = 0.1, 0.3, 0.5; z = 5.3−6.7); type B: Ca10[(PO4)5.7(CO3)0.45]CO3 · 0.3C6H11NO4 · 9H2O, and Ca10[(PO4)5.55(CO3)0.675]CO3 · 0.3C6H11NO4 · 9.2H2O. The solid phases have been characterized by chemical analysis, X-ray diffraction, thermogravimetric analysis, and IR spectroscopy.

Calcium hydroxylapatite/methylcellulose nanocomposite: Synthesis and properties

Organomineral nanocomposites (OMCs) of calcium hydroxylapatite Ca10(PO4)6(OH)2 (HA) and natural methylcellulose biopolymer [C6H7O2(OH)3 − x(OCH3)x]n (MC) were prepared by coprecipitation from aqueous solution in the Ca(OH)2-H3PO4-[C6H7O2(OH)3−x(OCH3)x]n-H2O system under biomimetic conditions (37°C). Synthesis products were identified by X-ray powder diffraction, IR spectroscopy, thermal analysis, scanning and transmission microscopy, and electron diffraction. The compositions and structural features of the OMCs and the crystallographic parameters, sizes, and morphology of HA nanoparticles in the OMCs were determined. The HA nanoparticles in the OMCs were found to interact with MC molecules to form agglomerates with sizes on the order of 150–200 nm.

Synthesis and Physicochemical Study of Chitosan-Containing Calcium Hydroxylapatites

The CaCl2-(NH4)2HPO4-(C6H11NO4)n-NH3-H2O system at 25°C was studied by the solubility (Tananaev’s residual concentrations) technique and pH measurements. The parameters providing for the coprecipitation of nanocrystalline (12.5–18.7 nm) calcium and chitosan hydroxylapatites were found. Calcium-deficient chitosan hydroxylapatites Ca9.8(PO4)6(OH)1.6 · xC6H11NO4 · yH2O, where x = 0.075 or 0.37 and y = 5.8 or 6.2, and stoichiometric calcium hydroxylapatites Ca10(PO4)6(OH)2 · xC6H11NO4 · yH2O, where x = 0.075, 0.1, 0.2, 0.37, 0.5, or 0.75 and y = 5.7–7.5, were synthesized. Solid phases were characterized by chemical analysis, X-ray powder diffraction, thermogravimetric analysis, and IR spectroscopy.

Synthesis and physicochemical characterization of nanocomposites of calcium hydroxylapatite-chitosan-multiwall carbon nanotubes

The synthesis and physicochemical characterization of nanocomposites of calcium hydroxylapatite-chitosan-multiwall carbon nanotubes (CNTs) was performed. The CaCl2-(NH4)2HPO4-(C6H11NO4)n-CNT-NH3-H2O system was studied by the solubility (Tananaev’s residual concentration) method and pH measurements at 25°C. Conditions for the joint precipitation of nanocrystalline calcium hydroxylapatite, chitosan, and multiwall CNTs were found. Nanocomposites with the general formula Ca10(PO4)6(OH)2 · x(C6H11NO4) · yCNT · zH2O, where x = 0.1, 0.2, and 0.5; y = 0.5, 2.0, 4.0, and 5.0; and z = 5.9–7.9. The solid phases were characterized by chemical, thermogravimetric, and X-ray diffraction analysis and IR spectroscopy.

Calcium hydroxyapatite in hydroxyapatite/graphene oxide/collagen nanohybrids

Interactions between calcium and phosphorus salts, graphene oxide (GO), and collagen (COL) in aqueous solutions have been studied in the CaCl2–(NH4)2HPO4–NH3–H2O–GO–COL system (25°C) using the solubility (residual concentrations) method and pH measurements. Syntheses were shown to yield composites comprising nanocrystalline calcium hydroxyapatite Ca10(PO4)6(OH)2) (HA), GO, and COL of empirical formula Ca10(PO4)6(OH)2 · xGO · yH2O · zCOL (x = 0.5, 1.0, or 2.0; y = 6.5–7.7; z = 3 or 5 wt %). Some physicochemical characteristics of synthesis products and the effects of the composite formulation on the crystallographic characteristics, sizes, and morphology of nanocrystalline hydroxyapatite (NCHA) were determined and some composition–structure–dispersion–property relationships in the HA/GO/COL composites have been analyzed using chemical analysis, X-ray powder diffraction, IR spectroscopy, thermogravimetry (TGA), differential scanning calorimetry (DSC), and electron microscopy.

Synthesis and physicochemical characteristics of calcium hydroxyapatite/multiwall carbon nanotubes/collagen nanocomposites

Calcium hydroxyapatite/multiwall carbon nanotubes/collagen nanocomposites were synthesized and subjected to physicochemical analysis. The system CaCl2-(NH4)2HPO4-multiwall carbon nanotubes-NH3-H2O-collagen was investigated at 25°C by the solubility method (Tananaev’s residual concentration method) and by pH measurements. Chemical, X-ray powder diffraction, and thermogravimetric analyses and IR spectroscopy showed that, in the system CaCl2-(NH4)2HPO4-multiwall carbon nanotubes-NH3-H2O-collagen under chosen synthesis conditions, nanocomposites comprising nanocrystalline calcium hydroxyapatite (NCHA), multiwall carbon nanotubes (CNT), and collagen form with the composition Ca10(PO4)6(OH)2 · xCNT · yH2O · z collagen, where x = 1–5; y = 5.5–7.7, and z = 3, 5, and 10 wt %. The obtained nanocomposites are the products of the coprecipitation of CNT, collagen, and NCHA, which forms in the system by the interaction of CaCl2 and (NH4)2HPO4.