S. Mielcarek

Changes in thermal and electrical properties of bone as a result of 1 MGy-dose γ-irradiation

Abstract Determination of temperature dependencies of electric conductivity and thermal properties by differential scanning calorimetry (DSC) allow to analyse the processes of charge and heat transport in the bone being a complex collagen–hydroxyapatite (HAP)–water system. Modification of the bone structure by high doses of γ-radiation changes the electrical and thermal properties of the bone. Electrical conductivity ( σ ) of the bone decreases with consecutive heating runs. The decrease in σ observed for irradiated samples was explained by the scission of the main chain of collagen macromolecule. Irradiation decreased the hydration level in the bone, its denaturation temperature and increased both enthalpy and entropy of the denaturation process.

High resolution Brillouin scattering studies of β-Gd2(MoO4)3; the bulk and surface phase transitions

We present here results of Brillouin scattering from bulk and surface phonons propagating in a well known ferroelectric–ferroelastic crystal β-Gd2(MoO4)3, in the temperature range covering the phase transition. Temperature dependences of the velocity of Rayleigh surface acoustic waves, propagating in a few planes of this crystal, have been calculated. The surface phonon velocities determined experimentally have been found to show a different character of temperature dependences, especially in the phase transition range.

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).

Atomic force microscopy and friction force microscopy studies of ferroelastic crystal surfaces

Abstract Topography and frictional properties of freshly cleaved surfaces of ferroelastic crystals: K 3 Na(SeO 4 ) 2 (KNSe), and NH 4 LiH 3 (SO 4 ) 4 (ALHS), and Gd 2 (MoO 4 ) 3 (GMO) were investigated by combined scanning and friction force microscopy (FFM) under ambient and UHV conditions. Atomic force microscopy (AFM) images revealed stepped surfaces with step heights corresponding to the multiplication height of crystal lattice constant fractions e.g., c /2 or c /4. A frictional contrast was observed between terraces which are separated by steps and between different domains of ferroelastic crystals. We suggest that the frictional contrast is due to different molecular orientations at different terraces and/or at different domains of a ferroelastic crystal, in the case of GMO, surface bends at the domain boundary with the angle estimated to be about 2.35°. It was also shown that the ALHS crystal surface can be modified (e.g., by changing the step profile and creation of the artificial bumps) by an AFM tip imaging with normal force above 100 nN.

Comparison of thermal properties of fish collagen and bovine collagen in the temperature range 298–670 K

The increased interest in fish collagen is a consequence of the risk of exposure to Creutzfeld-Jacob disease (CJD) and the bovine spongiform encephalopathy (BSE), whose occurrence is associated with prions carried by bovine collagen. Collagen is the main biopolymer in living organisms and the main component of the skin and bones. Until the discovery of the BSE, bovine collagen had been widely used. The BSE epidemic increased the interest in new sources of collagen such as fish skin collagen (FSC) and its properties. Although the thermal properties of collagen originating from mammals have been well described, less attention has been paid to the thermal properties of FSC. Denaturation temperature is a particularly important parameter, depending on the collagen origin and hydration level. In the reported experiment, the free water and bound water release processes along with thermal denaturation process were studied by means of the differential scanning calorimetry (DSC). Measurements were carried out using a DSC 7 instrument (Elmer-Perkin), in the temperature range 298-670K. The study material was FSC derived by acidic hydration method. The bovine Achilles tendon (BAT) collagen type I was used as the control material. The thermograms recorded revealed both, exothermic and endothermic peaks. For both materials, the peaks in the temperature range of 330-360K were assigned to the release of free water and bound water. The denaturation temperatures of FSC and BAT collagen were determined as 420K and 493K, respectively. Thermal decomposition process was observed at about 500K for FSC and at about 510K for BAT collagen. These results show that FSC is less resistant to high temperature than BAT collagen.

Band gap in hypersonic surface phononic lattice of nickel pillars

Brillouin light scattering was applied for investigation of surface wave propagation in phononic materials made of a silicon surface loaded with a nanostructure of nickel pillars. The results revealed the presence of phononic energy gap in the GHz range. The presence of such an energy gap was theoretically confirmed by the finite element method. The width of the energy gap was found to be related to the height of the pillars and was shown to be limited by the frequencies of the modes localized in the pillars. The modes were thoroughly analysed.

Elasto-optical effect in composite crystal based on urea

Behaviour of bulk phonons propagating in clathrate compounds based on thiourea has been studied by Brillouin spectroscopy for different polarizations of incident and scattered beams. Elasto-optical coefficients p12, p13, p44 and p31 have been determined for host–guest type crystals. Pressure dependence of the intensity of excitations propagating in a structure of the host–guest type has been studied by the non-invasive method of Brillouin spectroscopy.

One-dimensional modulation of the stripe in a surface phononic lattice: The effect on propagation of surface waves

Brillouin light scattering was applied for the investigation of surface waves propagation in phononic materials made of a silicon substrate loaded with a permalloy layer and a modulated nanostructure of aluminum stripes. The results revealed the impact of one-dimensional modulation of the surface phononic crystal on the propagation of surface acoustic waves along the modulated aluminum stripes. The dispersion relation was experimentally and theoretically investigated. The new modes propagating in the investigated structure are localized in the stripes and are defined.

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.

Pressure dependence of the elastic properties of composite host/guest type crystals

The elastic properties of host/guest type composite crystals, with urea as the host and an alkane as the guest, have been studied by Brillouin spectroscopy as a function of hydrostatic pressure. The effect of changing hydrostatic pressure in the range from 0 to 1400 bar on the propagation of acoustic phonons has been determined using three gases—helium, nitrogen and argon—as the pressure-exerting media.