Leszek Kubisz

Comparison of three rheological models of shear flow behavior studied on blood samples from post-infarction patients

Quantitative analysis of blood viscosity was performed on the basis of mathematical models of non-Newtonian fluid shear flow behavior (Casson, Ree-Eyring and Quemada). A total of 100 blood samples were drawn from clinically stable survivors of myocardial infarction, treated with aspirin or acenocoumarol and controls to these drugs. Whole blood and plasma viscosity were measured at a broad range of shear rates using a rotary-oscillating viscometer Contraves LS40. Numerical analysis of the experimental data was carried out by means of linear (for Casson) and non-linear regression for the remaining models. In the evaluation of the results, both the fit quality and physical interpretation of the models’ parameters were considered. The Quemada model fitted most precisely with the experimental findings and, despite the controversies concerning the relationship between in vivo tissue perfusion and in vitro rheological measurements, seemed to be a valuable method enhancing investigation possibilities of cardiovascular patients. Our results suggest that aspirin does not affect blood rheological properties, while acenocoumarol may slightly alter red cell deformability and rouleaux formation.

Dielectric studies of proton transport in air-dried fully calcified and decalcified bone.

Measurements of dielectric properties of calcified and decalcified bone were made in the electric field frequency range of 10(1)-10(5) Hz and at temperatures from 22 to 250 degrees C. The temperature dependencies of the complex dielectric constant of bone revealed two main molecular processes. The first process corresponds to the loss of water in the temperature ranges 22-160 degrees C and 22-210 degrees C for calcified and decalcified bone, respectively. The second is associated with the decomposition of collagen in bone, but this occurs only for decalcified bone above 210 degrees C. Analysis of polarization and conduction mechanisms for bone in the alpha-dispersion region was explained in terms of dielectric relaxation time and activation energy.

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.

Dielectric relaxation of air-dried horn keratin.

Dielectric measurements as a function of temperature and frequency are reported for horn keratin. The measurements of dielectric constant epsilon and loss factor epsilon, in keratin, were made in an electric field. This was done in the frequency range 10(1)-10(5) Hz and at temperatures from 22 to 220 degrees C. The samples contained 8% water by mass at room temperature at a relative humidity of 40%. A remarkable dispersion observed in the range of lower frequencies was attributed to interfacial polarization. The temperature dependences of the dielectric constants of horn keratin revealed the occurrence of two main molecular processes. The first process corresponded to the removal of water in the temperature range 22-170 degrees C. The activation energy associated with the release of loosely and strongly bound water, was about 35 and 7 kcal/mol, respectively. The second process, above 170 degrees C, was related to the denaturation of the alpha-helical phase in keratin.

Electric properties of non-irradiated and gamma-irradiated bone

Abstract Dielectric spectroscopy has been applied to study the effect of water and γ-irradiation on bone. Measurements were performed in the electric field frequency range of 101–105 Hz and at temperatures from 22 to 240 °C. The bone samples contained about 3% water by mass at room temperature. The doses of γ-irradiation were 5, 50, 100, 300 and 1000 kGy. The influence of water and γ-irradiation on the permittivity and conductivity of bone is significant at temperatures above 100 °C. Results of this paper would suggest that γ-irradiation initiates two important processes: cross-linking for doses 5 and 50 kGy and main-chain degradation for higher doses. Analysis of polarisation and conduction mechanisms for bone was interpreted on the basis of proton transport.

The effect of γ-irradiation on the temperature dependence of D.C. electrical conductivity of dry bone

The effect of gamma-irradiation with doses from 10 to 500 kGy on the electrical conductivity (g) of dry bone was studied. Temperature measurement of electrical conductivity were made from 393 to 533 K. The dependence obtained indicates the increase in g with temperature. An increase in irradiation dose resulted in a decreased g value for each dose up to temperature 462 K. Temperature 462 K was interpreted as the temperature of collagen melting point in dry bone. Above 462 K, g values were dose independent. A dose of 500 kGy shifted the melting point to lower temperature. In addition, the activation energy for the charge conduction process was calculated. Obtained values for electrical conductivity and activation energy were typical for dielectrics and indicated degradation of the organic component of bone.

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.

Time-dependent changes in dynamic mechanical properties of irradiated bone

The increased use of allograft tissue for musculoskeletal repair has brought more focus to the safety of allogenic tissue and the efficacy of various sterilization techniques. The currently available literature contains few examples of studies on long-lasting strains of bones but no example for irradiated bones. In this study the bovine femurs from a 2-year-old animal were machine cut and irradiated with the doses of 10, 15, 25, 35, 45 and 50xa0kGy. The dynamic mechanical analysis was performed at 1xa0Hz at the room temperature in a 3-point bending configuration for 2880xa0minutes. The final values of E and E″ were dose independent but they were reached at different periods. For this reason, so called critical point was introduced for the further analysis. All the examined sample groups were characterized by statistically significant lower values of the critical point in comparison with the control samples (p<0.05) but the biggest differences were observed between the control samples and the samples irradiated with the doses of 10, 15 and 25xa0kGy. Current results and literature review suggest that the dose of 35xa0kGy is the optimal dose for ionizing radiation sterilization.