Katalin Balázsi

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.

Spark plasma sintering of Si3N4/multilayer graphene composites

Abstract Mulitlayer graphene reinforced silicon nitride composites were prepared by spark plasma sintering to investigate the effect of the graphene addition on mechanical properties. The composites contained multilayer graphene (MLG) in various (0, 1, 3 and 5 wt%) content. Significantly higher fracture toughness of 8.0 MPa m1/2 was obtained at 1% MLG content, however, on further increasing the graphene content the toughness did not increase, but dropped to the value of the monolithic silicon nitride. The maximum hardness of 18.8 MPa was also obtained at 1% MLG, while at higher MLG contents it gradually decreased. Graphical Abstract

Biopolymer-Hydroxyapatite Scaffolds for Advanced Prosthetics

Biocompatibility in research and development of advanced prosthetics is a current problem faced by medical researchers. A major challenge in tissue engineering is to find materials and processing techniques that allow them to produce extracellular matrices (ECM) mimicking scaffolds that promote cell growth and organization into a specific architecture, inducing cell differentiation and subsequent cell function. The ideal tissue repair material thus should consist of synthetic biomaterials, such as natural polymers mimicking the mechanical and biological functionality of the ECM. Cellulose acetate membranes were used as scaffolds for microvascular cell growth. Hydroxyapatite (HA) is a natural ceramic (responsible for strength and stability in the human skeletal system) operable as a biocomposite coating to improve the biocompatibility of implant substrates. In this work, HA was prepared from low cost natural calcium source — eggshells. Its structural properties were investigated by scanning (SEM), transmission (TEM) electron microscopies and Fourier Transformed Infrared spectroscopy (FT-IR). The composition analyses of HA were measured by the total reflection X-ray fluorescence spectrometer (TXRF) and by prompt gamma activation analysis (PGAA). Hydroxyapatite added biodegradable scaffolds have been prepared by electrospinning method to enhance biological functionality.

Comparative Study of hydroxyapatite prepared from seashells and eggshells as a bone graft material

The aims of this study were to determine the physical properties of hydroxyapatite from seashells (sHA) and from eggshells (eHA), to analyze elements within sHA and eHA, and to compare the bone regeneration ability between sHA and eHA in a rat parietal bone defect model. The sHA and eHA particles had a similar morphology in scanning electron microscope images. From the Fourier-transform infrared absorbance spectra and X-ray diffraction results, both types of hydroxyapatite (HA) had the characteristics of pure HA. Inductively coupled plasma atomic emission spectroscopy results suggested that the sHA had higher levels of sodium and strontium than the eHA, whereas the eHA had higher levels of magnesium than the sHA. In μ-CT results, the mean bone mineral density of the sHA was significantly higher than the control at 4 weeks after the operation (p = 0.012). The mean bone volume of the eHA was significantly higher than the control at 8 weeks after the operation (p = 0.012). In the histological images at 4 weeks after the operation, foreign body multinucleated giant cells were observed around the agglomerated sHA particles, while there were fewer inflammatory reactions around the agglomerated eHA particles. The eHA group showed better results in bone formation than did the sHA group in this study.

Highly wear-resistant and low-friction Si 3 N 4 composites by addition of graphene nanoplatelets approaching the 2D limit

Graphene nanoplatelets (GNPs) have emerged as one of the most promising filler materials for improving the tribological performance of ceramic composites due to their outstanding solid lubricant properties as well as mechanical and thermal stability. Yet, the addition of GNPs has so far enabled only a very limited improvement in the tribological properties of ceramics, particularly concerning the reduction of their friction coefficient. This is most likely due to the challenges of achieving a continuous lubricating and protecting tribo-film through a high GNP coverage of the exposed surfaces. Here we demonstrate that this can be achieved by efficiently increasing the exfoliation degree of GNPs down to the few-layer (FL) range. By employing FL-GNPs as filler material, the wear resistance of Si3N4 composites can be increased by more than twenty times, the friction coefficient reduced to nearly its half, while the other mechanical properties are also preserved or improved. Confocal Raman spectroscopy measurements revealed that at the origin of the spectacular improvement of the tribological properties is the formation of a continuous FL- GNP tribo-film, already at 5 wt% FL-GNP content.

Mechanical Behavior of Bioactive TiC Nanocomposite Thin Films

Carbon-based nanocomposite thin films have large application potential because they possess unique mechanical properties, especially high hardness, high elasticity, and a low widely adjustable friction coefficient. In this work, relatively easy preparation of the nanocomposite Ti and C system with good mechanical properties and bioactivity was showed. Formation of physical and mechanical processes, relationship between the evolving structure and other properties of TiC films were studied. The films were deposited on oxidized silicon substrates by dc magnetron sputtering of Ti and C targets in argon and nitrogen at different temperatures between 25°C and 800°C. The composite films consisted of metallic nanocrystalls embedded in a carbon matrix. Highest hardness ~ 18 GPa and reduced modulus of elasticity ~ 205 GPa were obtained when the crystalline nanoparticles were separated by 2-3 nm thin carbon matrix consisting of amorphous and graphite-like carbon phases. In these films the H/E ratio in the both cases is ~ 0,1. Bioactivity studies were carried out on human osteoblast-like cell line MG-63. The number of initially adhering cells on day 7 after seeding was significantly higher on the TiC surface than on the control culture dishes. Good biocompatibility and bioadhesion of these surfaces are attained by a favourable combination of surface roughness and chemistry.

Biogenic Nanosized Hydroxyapatite for Tissue Engineering Applications

Hydroxyapatite (HAp) as resorbable porous bioceramics use as bone defect filling materials due to its remarkable biocompatibility and close chemical similarity to biological apatite present in bone tissues. One of perspective, non-expensive and environmental friendly material for hydroxyapatite preparation is eggshell. In this work, a simply method of HAp producing by mechanochemical activation from eggshells and the bone regeneration of HAp applied as bone tissue material were studied.

Structural and mechanical properties of milled si3n4/cnts composites by spark plasma sintering method

Multiwall carbon nanotubes were dispersed with a concentration of 3wt% in silicon nitride ceramic host. A high efficiency attritor mill has been used for an effective dispersion of the filler phase in the matrix. In this work we have developed a spark plasma sintering process (SPS) suitable to consolidate and tailor the microstructure of CNT-reinforced silicon nitride-based ceramic composites. Mechanical measurements, micro-indentation investigations of the hardness and fracture toughness have been performed. Scanning electron microscopy has been involved in order to reveal the microstructure of the resulting composites.

The Effect of Neutron Irradiation on the Mechanical Properties of Advanced Silicon Nitride Nanocomposites

There is a continuous need to develop structural and functional components to sustain fusion plasma under the very severe environment such as intense radiation or high temperature in fusion reactors. The reference Si3N4 and novel Si3N4 based nanocomposites with carbon nanotube, graphene or carbon black additions were irradiated in a controlled-temperature irradiation rig inside the Budapest Research Reaktor (BRR) at a temperature of 270 °C. In the irradiation channel of BRR the 1,5×1013 n/cm2 fluence can be reached in 700 hours. The effect of the neutron radiation on the mechanical properties of Si3N4 based nanocomposites with different carbon additives was investigated. In the case of 3-point bending test graphene and carbon nanotube added samples showed an increase in strength ~100-300 MPa after irradiation. 4-point bending strength measurements resulted in a significant increase of strength in the case of reference samples ~200-400 MPa and carbon nanotube added composites ~200-300 MPa after irradiation. Other samples showed no change in strength after irradiation.

Characterization and adhesion strength of porous electrosprayed polymer–hydroxyapatite composite coatings

The current study was initiated in order to evaluate the adhesion strength of thin and porous hydroxyapatite (Hap) coatings on titanium (Ti) substrates deposited by the low temperature electrospray...