Miroslav Miljković

Synthesis and properties of hydroxyapatite/poly-L-lactide composite biomaterials.

Calcium hydroxyapatite (HAp) and poly-L-lactide (PLLA) were synthesized chemically. The obtained HAp was of high purity and, after special thermal treatment, of high crystallinity as well. Synthesis of PLLA was performed using L-lactide as a monomer and nontoxic initiator. In this way a polymer of large molar weight (about 400,000) was obtained. The HAp and PLLA obtained were used as constituents of the HAp/PLLA composite biomaterial, a potential material for implants. The composite was obtained by mixing completely dissolved PLLA with granules of HAp. The composite was compacted by cold and hot pressing at pressures of 49.0-490.5 MPa and temperatures of 20-184 degrees C. The material obtained at optimum process parameters had a density of 99.6% and compressive strength of 93.2 MPa.

Dielectric and Ferroelectric Properties of BaTi1-xSnxO3 Multilayered Ceramics

Multilayered BaTi1-xSnxO3 (BTS) ceramics with different Ti/Sn ratios were produced by pressing and sintering at 1420 oC for 2 hours. X-ray diffractometry, scanning electron microscopy and energy dispersive spectroscopy were used for structural, microstructural and elemental analysis, respectively. The dielectric and ferroelectric behavior of sintered samples was studied, too. It is found that in ingredient materials, with increasing Sn content, the tetragonality decreases; Curie temperature moves towards room temperature, while the maximum of the dielectric constant increases, and also, they becomes less hysteretic. It is noticed that multilayered BTS ceramics with different Ti/Sn contents have a broad transition temperature and show a relatively high dielectric constant in a wide temperature range. It is shown that dielectric properties of these materials may be modified by a combination of different BTS powders as well as layers number.

Microstructure Evolution and Dielectric Properties of Nb/Mn and Dy/Mn Doped Barium Titanate Ceramics

Nb/Mn and Dy/Mn codoped BaTiO3 specimens, prepared by conventional solid-state procedure, were investigated regarding their microstructural and dielectric properties. The powders were doped with Nb2O5 and Dy2O3 with an amount of 0.1, 0.5 and 1.0 at% of dopants ions. The MnO content of 0.05 at% Mn was the same in both types of samples. The specimens were sintered in air at 1320 and 1350 °C for two hours. Microstructural and compositional studies were done by SEM equipped with EDS. In low doped BaTiO3 the grain size is around 1-3 μm, while in ceramics with high dopant content (1.0 at%) the grain size distribution was in the range of 3-10 μm. High dielectric constant is associated with small-grained microstructure, being 5000 for Dy-doped and 6500 for Nb-doped BaTiO3 sintered at 1350 °C. The specimens with low dopant content demonstrate the Curie-Weiss behavior in a paraelectric regime. A nearly flat permittivity response with temperature was obtained for specimens with 0.5 and 1.0 at% Dy content. Loss tangents were in the range of 0.03 - 0.32.

Hydrothermally processed 1D hydroxyapatite: Mechanism of formation and biocompatibility studies

Recent developments in bone tissue engineering have led to an increased interest in one-dimensional (1D) hydroxyapatite (HA) nano- and micro-structures such as wires, ribbons and tubes. They have been proposed for use as cell substrates, reinforcing phases in composites and carriers for biologically active substances. Here we demonstrate the synthesis of 1D HA structures using an optimized, urea-assisted, high-yield hydrothermal batch process. The one-pot process, yielding HA structures composed of bundles of ribbons and wires, was typified by the simultaneous occurrence of a multitude of intermediate reactions, failing to meet the uniformity criteria over particle morphology and size. To overcome these issues, the preparation procedure was divided to two stages: dicalcium phosphate platelets synthesized in the first step were used as a precursor for the synthesis of 1D HA in the second stage. Despite the elongated particle morphologies, both the precursor and the final product exhibited excellent biocompatibility and caused no reduction of viability when tested against osteoblastic MC3T3-E1 cells in 2D culture up to the concentration of 2.6mg/cm(2). X-ray powder diffraction combined with a range of electron microscopies and laser diffraction analyses was used to elucidate the formation mechanism and the microstructure of the final particles. The two-step synthesis involved a more direct transformation of DCP to 1D HA with the average diameter of 37nm and the aspect ratio exceeding 100:1. The comparison of crystalline domain sizes along different crystallographic directions showed no signs of significant anisotropy, while indicating that individual nanowires are ordered in bundles in the b crystallographic direction of the P63/m space group of HA. Intermediate processes, e.g., dehydration of dicalcium phosphate, are critical for the formation of 1D HA alongside other key aspects of this phase transformation, it must be investigated in more detail in the continuous design of smart HA micro- and nano-structures with advanced therapeutic potentials.

Apatite formation on nanomaterial calcium phosphate/poly-dL-lactide-co-glycolide in simulated body fluid

Simulated body fluid (SBF) is an artificial fluid which has ionic composition and ionic concentration similar to human blood plasma. Purpose This paper compares the interaction between the nanomaterial containing calcium phosphate/poly-DL-lactide-co-glycolide (N-CP/PLGA) and SBF, in order to investigate whether and to what extent inorganic ionic composition of human blood plasma leads to the aforementioned changes in the material. Methods N-CP/PLGA was incubated for 1, 2, 3, and 5 weeks in SBF. The surface of the material was analyzed on SEM-EDS and FTIR spectrometer, while SBF was subjected to pH and electrical conductivity measurement. Results Our results indicate that dissolution of the polymer component of the material N-CP/PLGA and precipitation of the material similar to hydroxyapatite on its surface are based on the morphologic changes seen in this material. Conclusions The mechanism of the apatite formation on the bioceramic surface was intensively studied and was considered crucial in designing the new biomaterials. The results obtained in this work indicate that N-CP/PLGA may be a good candidate for application to bone regeneration.

SEM-EDX Analysis of Bio-Oss® Granules After Incubation In Cell Culture Medium

The aim of this study was to analyze changes in the surface and chemical composition of Bio-Oss® granules after incubation in cell culture medium. Appropriate amount of Bio-Oss® material was incubated in Dulbecco’s Modified Eagle’s Medium (DMEM) at 37 °C for 3 days. After that, granules were dried, coated with gold and analyzed using scanning electron microscope (SEM) equipped with EDX (JEOL, JSM 5300). SEM analysis revealed that the surface of Bio-Oss® particles looks less grainy after incubation in DMEM. The impression is that an incubation in DMEM made erosion of cam bumps or that larger and wider reefs compared to the material before incubation are made by depositing of new material. Semi-quantitative analysis of calcium and phosphorous content in Bio-Oss® before and after incubation in DMEM was determined by EDX spectroscopy and results show that concentration of calcium and phosphorous ions increases after incubation in DMEM.

Sintering Behaviour and Microstructure Development in Electroconductive Si3N4-TiN Composites

The Si3N4-TiN composites offer the unique combination of thermal, mechanical and electroconductive properties making them suitable for wide range of engineering application. The use of the appropriate amount of TiN, which is dispersed in Si3N4 matrix, enables to achieve tailored electrical conductivity of composites, from high insulating to electroconductive ceramics. The use of TiN, ranging from 35 to 50%, together with appropriate sintering aids, resulted not only in fully dense compacts but also in compacts with a resistivity less than 10−1 Ωm as well. The addition of TiN has a marked effect in obtaining the uniform microstructure and improves also the mechanical properties such as the fracture toughness and flexural strength of composites as compared with those of the monolithic Si3N4 (Bellosi et al., 1992; Gogotsi, 1994; Boskovic et al., 1994; Choi et al, 1995). The electrical resistivity of Si3N4-TiN composites depends primarily on the amount of TiN content, but due to the percolation phenomenon and the probability of forming a conductive network, the conductivity depends in a great extent on the starting powders size and on the microstructure formed during the liquid phase sintering as stated by (1989), (1991) and (1991).

Properties of LiMn2O4 Powders Obtained by Ultrasonic Spray Pyrolysis

LiMn2O4 powders were synthesized by ultrasonic spray pyrolysis. By varying the cooling conditions, two samples of powders were obtained: quenched in water (Q) and spontaneously cooled to room temperature (SC). The crystal structure of the as-prepared powders was revealed by X-ray powder diffraction. Structure refinements confirm that SC sample crystallizes in Fd3m space group, while Q sample crystallizes in I4l/amd space group. Particle morphology was determined by scanning electron microscopy. Electrochemical intercalation and deintercalation were examined in galvanostatic regime.

Fractals and BaTiO3-Ceramic Microstructure Analysis

The complex grainy structure of BaTiO3 is difficult to describe by using traditional analytical or geometrical methods. Here, an attempt is made to establish new mathematical models based on both Euclidean and fractal geometrical methods. The first uses ellipsoidal approximations for barium-titanate grains describing the contact area as surface patches with an ellipsoidal boundary. The fractal method offers a better approach in describing the irregular and wavy surface of such contact zones and therefore, it defines aspects that are complementary to those defined by Euclidean methods. Electric, ferroelectric and opto-electric properties of BaTi03 are influenced strongly by the fractal dimension of the intergranular contact surfaces. This parameter is measured in a laboratory environment using SEM micrographs with different magnifications. The BaTiO3 samples examined have been sintered using different sintering pressures and temperatures. Then, the fractal dimension is calculated from a log-log diagram, and the grain contours are constructed using Iterated Function Systems connected with fractal interpolation.

The Sintering Temperature and the Ho2O3 Concentration Influence on BaTiO3-Ceramics Microstructure Fractal Nature

A new correlation between microstructure and doped BaTiO3-ceramics properties is developed based on fractal geometry. The BaTiO3-based materials structure can be controlled by using different sintering temperatures and additive concentrations. In this paper, Ho2O3-doped BaTiO3-ceramics microstructure properties have been investigated. The dopant concentration ratio is from 0.01 to 1 wt% of Ho2O3. The sintering has been done by using three different temperatures (1320, 1350, and 1380 °C). BaTiO3 microstructure and compositional studies were investigated by SEM (scanning electron microscope) equipped with EDS analysis. By using the fractal objects theory, the reconstruction of microstructure configurations such as grains contour shapes and the nature of intergranular contacts has been approximately established. Using fractal tools in studying BaTiO3-ceramics microstructure has a great significance for future components technology developments, materials function integrations, and miniaturization. The complementary statistical approach contributes to the investigation of BaTiO3-ceramic grains distribution and nature of intergrain contacts, which brings a major shift in the field of electronic components and alternative energy sources.