Csaba Balázsi

Development of nano-hydroxyapatite graft with silk fibroin scaffold as a new bone substitute.

PURPOSE This study involves a comparison between the bone regeneration of nano-hydroxyapatite (nHA), as derived from eggshells either with or without silk fibroin scaffolds, and the unfilled control in the rabbit calvarial bony defect model. MATERIALS AND METHODS Sixteen 4-month-old New Zealand white rabbits, with a mean weight of 2.8 kg (range, 2.5-3.0 kg), were used in this experiment. After the formation of bilateral parietal bony defects (diameter, 8.0 mm), either an nHA or an nHA+silk fibroin combination (nHA+silk) was grafted. The control was unfilled defect. The bone regeneration was evaluated by micro-computed tomography (μCT) and histomorphometric analyses at 4 and 8 weeks. RESULTS All measured variables of the μCT analysis were significantly higher in the grafted groups (nHA and nHA+silk) than in the unfilled control groups at both 4 and 8 weeks after operation (P < .05). On histomorphometric analysis, there was no significant difference between the groups at 4 weeks after operation. However, the nHA group exerted significantly higher bone regeneration (40.16% ± 8.27%) compared with the unfilled control group (25.66% ± 10.98%) or the nHA+silk group (16.62% ± 3.05%) (P < .05). CONCLUSION The nHA from eggshells exerted better bone formation than the unfilled control group on both μCT and histomorphometric analyses. Considering the rapid healing in bony defect and easy availability, the nHA from the eggshells could prove to be a good new bone substitute.

Nano-hydroxyapatite preparation from biogenic raw materials

Hydroxyapatite (HAp) was successfully produced from recycled eggshell, seashell and phosphoric acid. The phases obtained depended on the ratio of calcined eggshell/ seashell to phosphoric acid, the calcination temperature and the mechanochemical activation method (ball milling or attrition milling). The HAp structures were characterized by X-ray diffraction, scanning electron microsopy and infrared spectroscopy. Attrition milling was more effective than ball milling, yielding nanosize, homogenous and pure Hap.

Preparation and examination of multilayer graphene nanosheets by exfoliation of graphite in high efficient attritor mill

AbstractGraphene multilayers have been prepared by mechanical method based on milling graphite in high efficient attritor mill. The results showed that the best dispersion media is ethanol, and 10 hours of intensive milling proved to be the most efficient way to separate the graphite layers as it was shown by scanning electron microscopy and X-ray diffraction measurements.

Development of tungsten oxide hydrate phases during precipitation, room temperature ripening and hydrothermal treatment

Abstract Morphology and structure transformation of tungstic acid hydrate, H 2 WO 4 · n H 2 O precipitates, have been studied in aqueous phase with various levels of residual [Na + ] s at room temperature and at 120 °C in autoclave. Spindle-shaped morphology is characteristic for the washing product of the freshly prepared precipitates. Residual sodium is a persistent contaminant in H 2 WO 4 ·H 2 O. Sodium ion content in the solid phase has been found to control reaction route at hydrothermal treatment of tungstic acid hydrates. Morphological changes against [Na + ] s content at 120 °C are significant. Rectangular crystallites of WO 3 ·H 2 O, hexagonal platelets of WO 3 ·1/3H 2 O or their mixture can develop from the precursor spindle-shaped H 2 WO 4 ·H 2 O particles with various [Na + ] s at 120 °C. It is noteworthy that particles that ripened at room temperature display faces and axes seemingly corresponding to those of the crystallites developed in the hydrothermal process.

Synthesis and Sensing Properties to NH3 of Hexagonal WO3 Metastable Nanopowders

WO3 is an important kind of wide-bandgap semiconducting metal oxides, which has a very promising property in gas-detection behavior. It has several polymorphs with triclinic, monoclinic, orthorhombic structures being the stable forms of this oxide. However, by a method known as acid precipitation, new metastable open crystalline forms with hexagonal structure have been successfully synthesized. The nanopowders were characterized by SEM, TEM, and XRD, and their sensing response to reducing gases (NH3) was measured and compared to monoclinic WO3, showing a much better sensing property of the hexagonal WO3.

Comparative study of hydroxyapatite from eggshells and synthetic hydroxyapatite for bone regeneration

OBJECTIVES The objective of this study was to evaluate the physical properties of synthetic hydroxyapatite (sHA) and hydroxyapatite from eggshells (eHA) by Fourier-transform infrared (FT-IR) and x-ray diffraction (XRD) and to compare the regenerative ability of the bone using sHA and eHA in a rabbit calvarial defect model. STUDY DESIGN FT-IR and XRD were used to compare the physical properties of sHA and eHA. sHA was purchased from Sigma, and eHA was kindly donated from the Hungarian academy of science. Sixteen New Zealand white rabbits were used for the animal study. After the formation of a bilateral parietal bony defect (diameter 8.0 mm), either sHA or eHA was grafted into the defect. The defect in the control was left unfilled. Bone regeneration was evaluated by histomorphometry at 4 and 8 weeks after the operation. RESULTS The peak broadening of the XRD experiments were in agreement with scanning electron microscope observation; the sHA had a smaller granule size than the eHA. The eHA had impurities phases of CaO (International Center for Diffraction Data (ICDD) 075-0264) and Ca(OH)(2) (ICDD 072-0156). Total new bone was 17.11 ± 10.24% in the control group, 28.81 ± 12.63% in sHA group, and 25.68 ± 10.89% in eHA group at 4 weeks after the operation. The difference was not statistically significant (P > .05). Total new bone at 8 weeks after the operation was 27.50 ± 10.89% in the control group, 38.62 ± 17.42% in sHA group, and 41.99 ± 8.44% in the eHA group. When comparing the sHA group to the control group, the difference was not statistically significant (P > .05). However, the eHA group was significantly different from the control group (P = .038). When comparing the eHA group to the sHA group, the difference was not statistically significant (P > .05). CONCLUSIONS Both types of HA showed higher bone formation than the unfilled control. However, eHA had significantly higher bone formation than the unfilled control at 8 weeks after operation.

Tribology Study of Silicon Nitride-Based Nanocomposites with Carbon Additions

Tribology tests were conducted on silicon nitride-based nanocomposites with various carbon additions to explore the effects of microstructure, the type and quantity of carbon additives and the preparation routes on the behavior. The nanocomposites consisted of Si3N4 and C in the proportions of 1 – 10 wt % carbon nanotube (CNT), or carbon black (CB), or graphite, or graphene. Specimens were produced by hot isostatic pressing. X-ray diffraction and scanning electron microscopy were used to reveal phase composition and microstructure. Unlubricated ball-on-disk tribology tests with silicon nitride counter face were carried out at room temperature in ambient atmosphere. Contact profilometer was used to profile the wear tracks. The friction coefficients of the pure Si3N4 and Si3N4 samples with 3% CNT varied between 0,77-0,81. Addition of 10% graphite and 3% CB to Si3N4 resulted in friction coefficients of 0,83 and 0,72 respectively. Si3N4 samples with 3% graphene showed distinctly lower friction levels of 0,52 and smaller scatter of the measured values. The wear track study revealed that high graphene content in the Si3N4 matrix caused relatively big wear particles and an uneven wear track.

Characterizing the global dispersion of carbon nanotubes in ceramic matrix nanocomposites

The dispersion of single-walled carbon nanotubes in silicon nitride ceramic matrices has been investigated by small angle neutron scattering experiments. In contrast to electron microscopy investigations of fracture surfaces, neutron scattering measurements provide information on the bulk dispersion of nanotubes within the matrix. The scattering intensities reveal a decay exponent characteristic to surface fractals, which indicates that the predominant part of nanotubes can be found in loose networks surrounding the grains of the polycrystalline matrix.

Structural and biocompatible characterization of TiC/a:C nanocomposite thin films.

In this work, sputtered TiC/amorphous C thin films have been developed in order to be applied as potential barrier coating for interfering of Ti ions from pure Ti or Ti alloy implants. Our experiments were based on magnetron sputtering method, because the vacuum deposition provides great flexibility for manipulating material chemistry and structure, leading to films and coatings with special properties. The films have been deposited on silicon (001) substrates with 300 nm thick oxidized silicon sublayer at 200 °C deposition temperature as model substrate. Transmission electron microscopy has been used for structural investigations. Thin films consisted of ~20 nm TiC columnar crystals embedded by 5 nm thin amorphous carbon matrix. MG63 osteoblast cells have been applied for in vitro study of TiC nanocomposites. The cell culture tests give strong evidence of thin films biocompatibility.

The influence of residual sodium on the formation and reductive decomposition of hexagonal tungsten oxide

The metastable hexagonal form of tungsten trioxide (h-WO3) has recently been attracting much interest [1]. The synthesis routes of h-WO3 involve the dehydration of tungstic oxide hydrates, WO3 · nH2O (n= 0.3 [2, 3]; n= 0.9 [4]) or the oxidation of ammonium tungsten bronze [5–7], or ion-exchanging templating ions from hexagonal bronze [8]. Regarding the role and effect of possible residual chemical impurities, considerable uncertainty has remained. In this laboratory, we have prepared the oxide–hydrate precursor, WO3 · 1/3H2O by the route Na2WO4 · 2H2O→ H2WO4 ·H2O → WO3 · 1/3H2O [2, 9, 10]. According to a previous report, the formation of WO3 · 1/3H2O requires the presence of sodium in the reaction system, resulting in sodium incorporation in the WO3 · 1/3H2O phase [11]. This work focuses on the kinetic influence of sodium on the transformation/dehydration of WO3 · 1/3H2O into h-WO3 and on the hydrogen reduction of h-WO3 into elemental tungsten. The dehydration experiments of WO3 · 1/3H2O (of varying sodium contents) into h-WO3 were carried out either at isothermal conditions (300 ◦C, 15, 30 and 90 min, N2–O2 (80–20%) atmosphere) or in thermal gravimetry equipment (Mettler, Registrierender Vakuum-Thermoanalyzer, H2 (5N) ambient) where oxygen loss from the oxide during H2 reduction was also followed. X-ray powder patterns were recorded (at room temperature in a Guinier focusing camera using CuKα radiation, λ = 0.154051 nm) after each isothermal heat treatment and thermal analysis. The positions of the reflection lines on the film were determined by computer-controlled densitometric analysis [12]. Lattice parameters were obtained from the least-squares refinement of the d values of 23–26 reflections in the range 13◦ < 22 < 30◦. The calculated cell parameters for h-WO3 (JCPDS card 33-1387) samples obtained by dehydration of WO3 · 1/3H2O with [Na]= 163– 3420 ppm are collected in Table I. Morphology and grain size of h-WO3 and elemental tungsten were studied by scanning electron microscopy (SEM; Jeol 25). Transparent samples for transmission electron microscopy (TEM; Philips CM 20, operating at 200 kV) were prepared by depositing dispersed crystallites onto a holder, or by ion milling [14, 15]. TEM investigations reveal streaks in the diffraction pattern of h-WO3 (Fig. 1) showing the presence of stacking faults in the lattice. Second phases, precipitates or preferred sites for the allocation of sodium (Na+, Na2O) other than in the hexagonal channel (as suggested in [16]) have not been found; all samples of varying sodium contents, however, have been examined. Sodium concentration of the WO3 · 1/3H2O samples was found to influence the time of heat treatment needed for the dehydration/phase transformation as is demonstrated on XRD spectra and thermogravimetric (TG) plots. Details of the XRD spectra of samples isothermally heated for varying times show the “shift” of the 0 0 4 reflection of the orthorhombic WO3 · 1/3H2O to the position of the 0 0 2 reflection peak of h-WO3 (Fig. 2). This shift, indicating the dehydration of samples, is observed to be faster for the sample with 3400 ppm of sodium than that of samples with 160 and 1050 ppm. In the XRD patterns of the intermediate samples, temporary new peaks also appeared, which cannot be identified either among WO3 · 1/3H2O or h-WO3 peaks. TG curves of the dehydration of WO3 · 1/3H2O samples are plotted in Fig. 3a. In accordance with the observations at isothermal treatment shown in Fig. 2, the influence of the sodium content in the solid phase was also observed on the rate of dehydration. The WO3 · 1/3H2O sample with 160 ppm of sodium dehydrates with the minimal velocity. The dehydration velocity of the samples with 1000 and 3400 ppm of sodium increases with increasing sodium content. Samples with intermediate levels of sodium, 495 and 740 ppm, however, exhibit a greater dehydration velocity than samples with