M. V. Chaikina

Phase and elemental composition of silicon-containing hydroxyapatite-based coatings fabricated by RF-magnetron sputtering for medical implants

We studied by X-ray diffraction analysis, IR spectroscopy, and scanning electron microscopy (SEM) the phase composition and the structure of coatings based on silicon-containing hydroxyapatite (Si-HA) deposited by RF-magnetron sputtering. The sputtering target contained two phases (apatite and tricalcium phosphate) and was produced by the ceramic technology from a single-phase mechanically activated powder precursor. The structure of the coating deposited by sputtering from the two-phase target was single phase (hydroxyapatite) and textured in the (002) direction. During deposition, silicate anions partially replaced phosphate ions in the apatite lattice.

Studies of oxygen transport mechanism in electrolytes based on doped lanthanum silicate with apatite structure using techniques of oxygen isotopic heteroexchange and impedance spectroscopy

The work presents the results of studying the mechanism of oxygen transport for a new promising class of oxygen-containing electrolytes based on lanthanum silicate with an apatite structure using impedance spectroscopy and isotopic oxygen heteroexchange. At 1000 K, in the case of samples with an optimum composition including codoped Fe and Al, σ ∼ 3 × 10−3 to 10−2 S/cm and D* reaches ∼10−8 cm2/s, which is close to the values of YSZ and Ce0.9Gd0.1O2 − δ (GDC). Lower energies of conductivity activation and oxygen diffusion for doped apatites (∼0.5–0.8 eV instead of ∼1 eV for GDC) and also equivalence as regards exchange of all oxygen atoms within apatite agree with the model, in which oxygen mobility is determined by a nonlinear cooperative migration process of oxygen atoms with fast exchange between interstitial and regular sites.

Structure and properties of La- and Si-incorporated calcium phosphate coatings

The physical and chemical properties of calcium phosphate coatings deposited by means of the microarc oxidation method in electrolytes based on simultaneously La- and Si-substituted hydroxyapatite with various concentrations of the substituents (Ca10–xLax(PO4)6–y(SiO4)y(OH)2, x = y = 0.2 and 0.5) under different oxidation voltages from 150 to 350 V are investigated. It is shown that with increasing oxidation voltage the coating thickness and surface roughness increase linearly from 20 to 130 μm and from 2 to 8 μm, respectively. It is established that coatings deposited under voltages in the range 150–250 V have an amorphous structure and, as a consequence, a high rate of bioresorption. The increase in the process voltage to 300–350 leads to the formation of the crystalline phases CaHPO4 and β-Ca2P2O7 in coatings. With increasing voltage, the La concentration increases in coatings and the Si concentration remains almost unaltered. In this case, the maximum La and Si amounts in coatings are equal to 0.22 an...

Biocompatible nanostructured coatings based on calcium phosphates prepared by means of rf-magnetron sputtering deposition

The aim of this study was to prevent the problems associated with implants failure. Biocompatible nanostructured thin films of either Si- or Ag-containing non-stoichiometric hydroxyapatite (HA) were deposited by method of radio-frequency (rf) magnetron sputtering. Plates of Ti, Ti6Al4V and 316 L SS were used as substrates. The thin coatings were characterized by EDX, ESEM, XRD, IR spectroscopy, HRTEM, nanoindentation and scratch-test. HRTEM observations of the coatings showed a nanocrystalline structure mixed with amorphous regions. It was found that the morphology, structure and the preferred orientation of the films are greatly affected by the parameters of deposition (rf-power, substrate temperature and voltage bias). The as-deposited modified CaP-based coatings are dense, pore-free and their composition resembles that of the precursor target composition. The Si- and Ag- containing HA coatings had a hardness of 10-12 GPa. A low rf-power (30 W) resulted in amorphous or low crystalline CaP coating structure. An increase in rf-power (>; 200 W) induced the coating crystallization. The occurrence of the different structure types is described as function of the bias voltage and temperatures. The negative substrate bias allowed to vary the Ca/P ratio in the range of 1.53 to 4. In vitro biocompatibility assessments of the films using the MG63 osteoblast-like cells indicated excellent cell adherence and surface colonization. Si-containing rf-magnetron films promote osteogenic differentiation of human stromal stem cells in vitro. The coatings are prospective to be used in clinical practice: in stomatology or craniofacial medicine, where the leaching of toxic ions from the substrate is necessary or the initial material surface porosity for a further bone in growth should be preserved.

The influence of solid precursors nature on structural, textural and surface properties of framework zirconium phosphates synthesized via mechanochemical activation

Abstract The framework zirconium phosphates with incorporated La 3+ and NH 4 + cations were synthesized via mechanical activation of solids followed by the hydrothermal treatment. Their phase composition, local bulk structure, surface properties and microstructure appear to be defined both by the structure of amorphous zirconium phosphates formed via mechanical activation of solids depending on precursors acidity and reactivity and by the pH-dependent mechanism of subsequent crystallization during hydrothermal treatment.

The microstructure and properties of framework zirconium phosphates based nanocomposites : catalysts of alkane isomerization

Abstract Nanocomposites based upon framework zirconium phosphates with supported WO3, MoO3 and Pt nanoparticles were synthesized via the incipient wetness impregnation of high-surface-area mesoporous phosphate samples with water solutions of corresponding salts followed by drying and calcination. The structure and surface properties of nanocomposites were studied by using combination of structural and spectral methods. Due to a strong interaction between supports and supported species, the structure of the latter differs considerably from that of the bulk phases. Surface acid centers typical for zirconium phosphates disappear suggesting their participation in bonding nanoparticles of promoters. Instead, new types of strong acid sites associated with tungsten oxide clusters emerge. The effect of these promoters on performance of zirconium phosphates in the reaction of pentane and hexane isomerization is considered.

Solid-state NMR and computational insights into the crystal structure of silicocarnotite-based bioceramic materials synthesized mechanochemically

In this work, we report the results of a detailed structural study of a promising bioceramic material silicocarnotite Ca5(PO4)2SiO4 (SC) synthesized from mechanochemically treated nanosized silicon-substituted hydroxyapatite by annealing at 1000°C. This novel synthetic approach represents an attractive and efficient route towards large-scale manufacturing of the silicocarnotite-based bioceramics. A combination of solid-state nuclear magnetic resonance (NMR), powder X-ray crystallography and density function theory (DFT) calculations has been implemented to characterize the phase composition of the prepared composite materials and to gain insight into the crystal structure of silicocarnotite. The phase composition analysis based on the multinuclear solid-state NMR has been found in agreement with X-ray powder diffraction indicating the minority phases of CaO (5-6wt%) and residual silicon-apatite (7-8wt%), while the rest of the material being a fairly crystalline silicocarnotite phase (86-88wt%). A combination of computational (CASTEP) and experimental methods was used to address the anionic site disorder in the silicocarnotite crystal structure. Distorted [OPO3] pyramids have appeared as an important structural motif in the SC crystal structure. The ratio between regular [PO4] and distorted [OPO3] tetrahedra is found between 2:1 and 3:1 based on XRD experiments and CASTEP calculations. The natural abundance 43Ca magic angle spinning NMR spectra of silicocarnotite are reported for the first time.

Lanthanum–silicate–substituted apatite synthesized by fast mechanochemical method: Characterization of powders and biocoatings produced by micro–arc oxidation

Lanthanum-silicate substituted apatite with equal concentrations of the substituents in the range of 0.2-6.0 mol were produced by a fast method - mechanochemical synthesis. This method makes it possible to synthesize a nanosized single-phase product by activating reaction mixtures containing CaHPO4, CaO, La(OH)3 and SiO2·H2O for 25-30 min in AGO-2 and AGO-3 planetary mills. The structure of the apatites was investigated by the FTIR and XRD methods. It was found that the synthesized samples with substituent concentrations up to 2 mol are substituted oxy-hydroxyapatites, at higher concentrations, they are substituted oxyapatites. The mechanochemically synthesized apatite with a substituent concentration of 0.5 mol was used for depositing biocoatings on titanium substrates by the micro-arc oxidation method. The structure of the coatings is mainly amorphous. In vitro biological tests demonstrated high biocompatibility of the coatings and the absence of cytotoxic action on mesenchymal stem cells.

Mechanochemical Synthesis of Sr-Substituted Hydroxyapatite

We demonstrate that a nanoparticulate Sr-substituted carbonate hydroxyapatite can be prepared by fast mechanochemical synthesis, without further annealing of the material. The synthesis process takes 30 min and yields single-phase products. We have obtained a series of Ca10–xSrx(PO4)6(OH)2 samples with x = 0–2.

Lanthanum-silicon-substituted hydroxyapatite: Mechanochemical synthesis and prospects for medical applications

The paper presents the results of mechanochemical synthesis of hydroxyapatite (HAP) with simultaneous substitutions of lanthanum (La3+) for calcium ions and silicate ((SiO4)4−-group) for the phosphate group with the substituent concentrations in the range 0.2–2.0 mol per HAP mol. The use of Si-substituted HAP as a coating material promotes accelerated osteosynthesis and osteointegration of implants into the bone tissue. The replacement of calcium ions by La3+ in the HAP structure plays an antimicrobial role preventing inflammatory processes. Annealing-induced variations in the lattice parameters of synthesized samples indicate the substituent incorporation into the HAP structure. It is known that complex compounds with lanthanides are used for cancer chemotherapy. In particular, La plays a key role in the course of treatment of injured defects of bone tissue. In addition, La-substituted HAP can be used for filling bone defects and coating implants in postoperational areas affected by bone cancer.