Piotr Biskupski

Radiation sterilized bone response to dynamic loading.

Allogeneic bone grafts are used on a large scale in surgeries. To avoid the risk of infectious diseases, allografts should be radiation-sterilized. So far, no international consensus has been achieved regarding the optimal radiation dose. Many authors suggest that bone sterilization deteriorates bone mechanical properties. However, no data on the influence of ionizing radiation on bone dynamic mechanical properties are available. Bovine femurs from 2-year old animal were machine cut and irradiated with the doses 10, 15, 25, 35, 45 and 50 kGy. Dynamic mechanical analysis was performed at 1-10 Hz at the temperature range of 0-350 °C in 3-point bending configuration. No statistically significant differences in storage modulus were observed. However, there were significant decreased values of loss modulus between the samples irradiated with doses of 10 (↓14.3%), 15, 45 and 50 kGy (↓33.2%) and controls. It was stated that increased irradiation dose decreases the temperature where collagen denaturation process starts and increases the temperature where the collagen denaturation process finishes. It was shown that activation energy of denaturation process is significantly higher for the samples irradiated with the dose of 50 kGy (615 kJ/mol) in comparison with control samples and irradiation with other doses (100-135 kJ/mol).

Dielectric dispersion in [N(C2H5)4]2ZnCl4 single crystal

Abstract Temperature dependence of the complex dielectric permittivity of [N(C2H5)4]2ZnCl4 crystal was measured in the frequency range 300 Hz ÷ MHz. Jump-wise changes in the real and imaginary components of ε* were observed for the three crystallographic directions at the phase transition temperature. The dielectric dispersion clearly apparent in the high-temperature phase, rapidly disappears at the phase transition. The anomalous changes in the dielectric permittivity are related to vibrations of the tetraethylammonium ion. The activation energy of these vibrations amounts to 40 kJ/mol.

Segmental dynamics in poly(vinylidene fluoride) studied by dielectric, mechanical and nuclear magnetic resonance spectroscopies

The dynamics of segmental motions in semicrystalline poly(vinylidene fluoride) has been studied by means of dielectric and mechanical spectroscopies and nuclear magnetic resonance method. The relaxation data, obtained from different techniques, over a wide temperature and frequency range, have been analyzed in terms of main-chain segmental motion, described by phenomenological Havriliak–Negami function. The results indicate that the correlations between local conformational transitions in the amorphous phase are intermediate. Good agreement between the experimental and calculated data offers a contribution to the understanding of molecular dynamics in the glassy state of the polymer.

The influence of low temperatures on dynamic mechanical properties of animal bone

The influence of low temperatures on dynamic mechanical properties of animal bone Different preservation methods are currently used in bone banks, even though their effects on allograft quality are not fully understood. Freezing is one of the most popular methods of preservation in tissue banking. Yet, there is not a lot of data on dynamic mechanical properties of frozen bone. Material used in this study was femoral bones from adult bovine that were machine cut and frozen to the temperature 140°C. Both elastic modulus and loss modulus were measured at 1, 3, 5, 10, and 20 Hz in the temperature range of 30-200°C. Differences between frozen and control samples were observed. The frequency increase always led to the increase in elastic modulus values and decrease in loss modulus values. Freezing reduced the elastic modulus values of about 25% and the loss modulus values of about 45% when measured at 20°C.

STM/STS investigation of carbon nanotubes deposited on Bi2Te3 surface

This paper reports our scanning tunneling microscopy and spectroscopy (STM/STS) study of double-walled and multi-walled carbon nanotubes (CNTs) of different diameter deposited on Bi2Te3 (narrow gap semiconductor). The approximate diameter of the studied double-walled and multi-walled CNTs was 2 nm and 8 nm, respectively. Crystalline Bi2Te3 was used as a substrate to enhance the contrast between the CNTs and the substrate in the STS measurements performed to examine peculiarities of CNT morphology, such as junctions, ends or structural defects, in terms of their electronic structure.

Structure of TEA2ZnCl4 crystal surfaces studied by AFM

The surface of the TEA2ZnCl4 crystal has been studied by the atomic force microscope for the fresh (as-obtained) samples and for the samples cooled below = 223.2 K at a rate of 10° min−1. The images obtained have revealed strong cracking of the crystal surface. For the (110) surface the cracks were perpendicular to the cleavage planes, whereas the (001) surface was completely changed. The changes lead to the brightening of the crystal samples and may suggest the ferroelastic deformation in microregions. No classical ferroelastic domain structure has been observed in the low-temperature phase.

STS INVESTIGATIONS OF METALLIC NANOSTRUCTURES DEPOSITED ON Bi2Te3

Bi2Te3 has attracted attention due to its potential applications in the microfabrication of integrated thermoelectric devices. It is also interesting to study the metallization process of this compound. Metallic nanostructures were deposited by means of an electron gun evaporator in ultra high vacuum (UHV) conditions (10-8 Pa) on the freshly cleaved 0001 surface of the crystal Bi2Te3. Measurements were conducted using the commercially available Omicron UHV scanning tunneling microscope (STM). Scanning tunneling spectroscopy (STS) measurements were performed using current imaging tunneling spectroscopy (CITS), and subsequent calculation of the dI/dV maps. Metallic characteristics were observed on nickel islands since early stages of the growth. CITS and dI/dV maps showed distinct contrast between the substrate and metallic islands. Similar contrast was not observed in the case of titanium, most probably due to an intercalation process. Occurring of such a process was confirmed by the appearance of the superlattice structure.