Dielectric properties of the non-glycated and in vitro methylglyoxal-glycated cornea of the rabbit eye.

The dielectric properties of the non-glycated and in vitro methylglyoxal-glycated cornea of the rabbit eye were tested in the frequency range of 200 Hz to 100 kHz of the electric field and at temperatures of 25 to 140 °C. The denaturation temperature (Td) for the non-glycated cornea and the non-enzymatically glycated cornea are approximately 45 and 55 °C, respectively. The mechanism of proton conduction up to Td in a glycated cornea requires more energy, i.e. more than twice the activation energy (ΔH) than in non-glycated tissue. The dielectric spectra for both examined tissues showed the same characteristic frequency of about 7 kHz assigned to the orientation relaxation time of the polar side groups inside the corneal stroma. These results may be useful in the surgical treatment of the cornea using conductive keratoplasty and in tissue engineering for clinical applications to regenerate this tissue. The medical use of these physico-biological techniques is important because the human cornea protects all eye tissues from various environmental factors.

Dielectric response to thermal denaturation of lenses in healthy and diabetic rabbits.

The relative permittivity and conductivity of healthy and alloxane-induced diabetic rabbits lenses were measured over a frequency range of 500 Hz to 100 kHz in an electric field and at temperatures from 25 to 150 °C. The dielectric spectra for both tissues showed two separate relaxations with a characteristic frequency of around 4 and 25 kHz assigned to the cortical and nuclear zones, respectively. These two dispersions are due to the interfacial polarization at the surface of the α-crystallin molecules. The denaturation temperature for the non-diabetic lens and the diabetic lens is approximately 70 and 80 °C, respectively. Moreover, the relative permittivity and conductivity values are higher in the diabetic lens than in the non-diabetic tissue at the same temperature and frequency. Our dielectric studies provide a better understanding of the thermal stability of crystallin-water complexes in normal and diseased human lenses.

Dielectric properties of healthy and diabetic alloxan-induced lenses in rabbits.

The dielectric properties of the eye lens were studied for healthy and alloxane-induced diabetic rabbits in the frequency range from 500 Hz to 100 kHz electric field and temperatures from 25 to 50 °C. In the full temperature range, the average relative permittivity and dielectric loss values for a healthy lens are lower than those recorded for diabetic tissue. Dielectric relaxation of polar amino acids on the alpha-crystallin surface with a characteristic frequency of 7 kHz in the range of 25-50 °C for healthy and diabetic samples is accompanied by the activation energy of proton conductivity with an average values of 33 and 39 kJ mol-1, respectively. The permittivity decrement, which characterizes the size of the dielectric dispersion with a central relaxation time of 0.023 ms for a diabetic sample, is more than twice as high as for a healthy sample. Measurements on the rabbit eye lens were carried out at ambient temperature above and below the physiological range, since these conditions provide an appropriate pattern of dielectric behavior for the diagnosis of clinical dysfunction of the human lens.

The effect of different methods of cross-linking of collagen on its dielectric properties.

This paper reports on the effect of different methods of collagen cross-linking on its dielectric properties. In order to obtain collagen-hyaluronic acid (HA) scaffolds, collagen was first dehydrated by a combination of thermal and vacuum drying (DHT) and then treated with the chemical reagent carbodiimide (EDC/NHS) for final cross-linking. The measurements of the relative permittivity epsilon' and the dielectric loss epsilon'' for all materials were carried over the frequency range of 10 Hz-100 kHz and at temperatures from 22 to 260 degrees C. The results for these samples reveal distinct relaxation processes at low temperatures, below 140 degrees C and at higher temperatures as broad peak around 230 degrees C. The first and second relaxation are associated with changes in the secondary structure of collagen accompanied by the release of water and with the denaturation of dry collagen, respectively. The influence of cross-linking on the permittivity of collagen is significant over the entire temperature range.

Selecting the correct scaffold model for assessing of the dielectric response of collagen-based biomaterials.

Fish collagen (Col) was cross-linked using two methods: dehydrothermal treatment (DHT) and 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) in the presence of N-hydroxy-succinimide (NHS). For the samples marked Col, Col-DHT and Col-EDC/NHS, dielectric properties were measured in the frequency range from 100 Hz to 100 kHz and temperatures from 25 to 145 °C. In the full temperature range, the average values of relative permittivity and dielectric losses for Col samples are lower than those recorded for Col-DHT and Col-EDC/NHS samples. The peak temperature of the dielectric parameters attributed to the denaturation temperature for Col, Col-DHT and Col-EDC/NHS, respectively, is about 75 °C, 83 °C and 89 °C. In addition, the values of these parameters are much higher in Col-EDC/NHS than in Col-DHT at the same temperature and frequency. The permittivity decrement and conductivity increment, respectively, for Col-EDC/NHS are about 62 and 32 times greater than those given by Col-DHT, which is a consequence of the EDC/NHS crosslinking action. Our electrical and dielectric studies of fish Col cross-linked by EDC/NHS or DHT provide deeper insight into the structure of collagen materials and help improve the synthesis of Col-based scaffolds for tissue engineering.

Dielectric relaxation of a protein-water system in atherosclerotic artery wall.

Measurements of the dielectric properties of healthy and atherosclerotic human artery tissues were made in the frequency range of 100 Hz-100 kHz and temperatures from 22 to 260 degrees C. The temperature dependencies of the dielectric parameters for healthy tissues reveal distinctively the temperature ranges corresponding to the release of water up to 200 degrees C and the decomposition processes of elastin and collagen, above this temperature. The influence of atherosclerosis on the dielectric properties of artery tissues is significant in the whole temperature range. The relative permittivity for atherosclerotic tissues at the same temperature is much lower than for the healthy tissues. This suggests, that the polarization in atherosclerotic tissues due to protons hopping between a smaller number of sites than in healthy tissues, as a results of the thermal degradation of collagen-water. The data obtained above 200 degrees C indicate that the atherosclerosis induces the higher physico-chemical changes in the collagen when compared to elastin.

Dielectric study of interaction of water with normal and osteoarthritis femoral condyle cartilage.

The main goal of this paper is the in vitro study of healthy and osteoarthritis (OA) human cartilage using the dielectric spectroscopy in the alpha-dispersion region of the electric field and in the temperatures from 25 to 140°C. The activation energy of conductivity needed to break the bonds formed by water in the extracellular matrix takes the average values of 61kJ/mol and 44kJ/mol for the control and OA cartilages, respectively. At 28°C, the small difference appears in the permittivity decrement between the control and OA cartilages, while the conductivity increment is about 2 times higher for the control tissue than that for the OA tissue. At 75°C, the conductivity increment for both of these samples is 8 times higher than their respective permittivity decrement. In addition, at 140°C the values of these both parameters for the OA tissue decrease by 8 times as compared to those recorded for the control sample. The relaxation frequency of about 10kHz is similar for both of these samples. The knowledge on dielectric properties of healthy and OA cartilage may prove relevant to tissue engineering focused on the repair of cartilage lesions via the layered structure designing.

Dielectric properties of the collagen-glycosaminoglycans scaffolds in the temperature range of thermal decomposition.

Dielectric spectroscopy has been applied to study the decomposition process of unmodified collagen and chondroitin sulfate (CS)- and hyaluronic acid (HA)-modified collagen. Measurements were performed over the frequency range from 10 Hz to 100 kHz and at temperatures from 22 to 260 degrees C. According to the Kramers-Kronig relationship a dispersion is apparent in both epsilon' and epsilon'' for the three materials below 140 degrees C and at higher temperatures as a broad peak around 220-230 degrees C, respectively. The values of epsilon' and epsilon'' at the same temperature for constant frequency are higher in HA-modified collagen than in the unmodified collagen. However, small differences are shown in these parameters between CS-modified collagen and unmodified collagen. The observed dispersion around 220-230 degrees C corresponds to the decomposition of unmodified and CS- and HA-modified collagen. Power-low responses are observed for the frequency dependence of ac conductivity for unmodified and modified collagen. The behaviour observed for temperature dependencies of the exponent n for the three materials is considered to be related to the proton polarization and conduction processes.

Dielectric properties of a protein-water system in selected animal tissues.

Dielectric spectroscopy has been applied to study aspects of the organization of water in selected animal tissues (tendon, bone and horn). The measurements of the relative permittivity epsilon' and the dielectric loss epsilon'' were carried over the frequency range of 10-100 kHz and at temperatures from 22 to 240 degrees C. The water content was 10% for bone and horn, and 22% for tendon by mass at room temperature at a relative humidity of 70%. The temperature dependencies of epsilon' and epsilon'' reveal distinctively the temperature ranges corresponding to the release of water in temperatures up to about 200 degrees C for all tissues and the melting of the crystalline structure only for tendon and horn, above this temperature. The frequency dependencies of epsilon' and epsilon'' show a remarkable dispersion in the low-frequency at selected temperatures up to 200 degrees C for all tissues due to the release of the loosely and strongly bound water. The results were discussed in terms of the interfacial (Maxwell-Wagner) polarization and polarization mechanism involving hopping charge carriers interacting with the bound water molecules. The information on the effect of temperature, water content and frequency of the electromagnetic field on the dielectric behaviour of the tissues studied is of importance in the design and construction of medical diagnostic or therapeutic instruments based on the use of electric signals.

Dielectric relaxation of normothermic and hypothermic rat corneas.

This paper aims at the presentation of the results of in vitro research on the dielectric properties of the cornea specimen collected from the rats subjected to in vivo hypothermia. The average values of the relative permittivity and dielectric loss are about 40% higher for the hypothermic cornea than those for the normothermic tissue at the same water content of 12% for both samples and at 25°C. Whereas, at 50°C this effect of increase in the dielectric properties of the hypothermic cornea when compared to the normothermic one is observed clearly only in the relative permittivity of about 19%. In the temperature range of 25-50°C, the activation energy of conductivity associated with the release of loosely bound water takes the average values of 45kJ/mol and 30kJ/mol for the normothermic and hypothermic corneas, respectively. The study provided information on dielectric polarization and conductance mechanisms in the cornea which may be helpful in interpreting clinical results of human cornea examination, currently obtained by means of such electrodiagnostic methods as conductive keratoplasty, electroretinography or electrooculography.

Temperature variation of the relaxation time of alpha-dispersion for gamma-irradiated collagen.

The effect of gamma irradiation, with doses from 10(2) to 10(3) kGy, on the dielectric relaxation time of solid-state collagen was studied. Temperature measurements of the relaxation time were made over a range of frequency of the electric field from 10(1) to 10(5) Hz and at temperatures from 298 to 480 K. The samples contained 0.06 g H2O/g dry collagen. The dependencies obtained indicate that values for the relaxation time decrease with increasing temperature for all samples of collagen. In addition, an increase in the irradiation dose resulted in a decreased relaxation time for collagen at each temperature studied. These changes can be interpreted on the basis of proton conduction processes. Such effects occurring in a heterogeneous medium such as a collagen-water system are caused by the localized jumping of free protons between neighbouring sites. In the system of irradiated collagen studied, the sites are formed by structural water molecules, the products of its radiolysis and also by elements of the damaged first-order structure of the collagen macromolecule.

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.

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.

Analysis of the dielectric properties of keratin in the alpha-dispersion electric field region.

The dielectric method has been applied to study the relaxation mechanisms of non-irradiated and gamma-irradiated keratin-water systems in the electric field frequency range of 10(1)-10(5) Hz and at temperatures from 22 to 190 degrees C. Measurements were performed for keratin samples containing 3% water by mass at room temperature. The doses of gamma-irradiation were 5, 50 and 200 kGy. The influence of water and gamma-irradiation on the dielectric behaviour of keratin was negligible up to 120 degrees C but significant in the temperature range of 140-190 degrees C. In the first temperature range, the motion of polar side chains was characterised by a low activation energy of 11 kJ mol(-1), while longer relaxation times varied from 418 to 155 ms. In the range 140-190 degrees C, the release of the strongly bound water in keratin samples irradiated with doses of 0-50 kGy was evidenced by the high value of the activation energy of 84 kJ mol(-1) and shorter relaxation times varying from 43 to 3 ms. The value of the activation energy decreased to 55 kJ mol(-1) for keratin samples irradiated with 200 kGy as a result of degradation of the hydrogen bond between the water and polar groups of the main chain of the macromolecule. The results presented may be useful in bio-electrical impedance analysis, for physiological and clinical research. The method applied in vivo should permit detection of changes in the stratum corneum induced by water, ionising radiation, cosmetics and diseases such as fibromyalagia or diabetic foot ulcers.

Dielectric properties of hypothermic rat artery.

The temperature and frequency dependencies of the dielectric parameters for the rat artery are used to analyse effects of hypothermia on this tissue. Measurements were performed over the frequency range 500 Hz to 100 kHz and at temperatures from 19 to 60°C. The artery samples contained about 12% water by mass at room temperature at a relative humidity of 70%. The frequency dependencies of the loss tangent for the control, mild hypothermic and moderate hypothermic artery exhibit two peaks at 2 kHz and 35 kHz in the α-dispersion region. The results were discussed in terms of the distribution of relaxation frequencies and the activation energy for the conduction and polarization mechanisms particularly in the elastin-water and collagen-water systems. The knowledge about dielectric behavior of the hypothermic rat artery in vitro is important due to clinical application of local and systemic hypothermia.

Dielectric phenomena associated with the keratin-glucose interactions of nail plate.

In this study, we analyzed the effect of water and frequency on the dielectric properties of the nail plate in healthy individuals and in diabetic patients. The temperature dependencies of the loss tangent for both healthy and diabetic nail represent the relation between the electrical energy lost and stored in keratin-glucose-water complexes of this tissue. The differences between these materials concern the temperature ranges in which there appears the decomposition of loosely bound water. The effect of glycation on the loss tangent of the wet and the dry nail is supported by higher values of this parameter than in those describing the healthy samples in the whole temperature range and above 100°C, respectively. In addition, glycation lead to distinct increase in the dielectric relaxation decrement in permittivity and dielectric loss between the frequency of 500 Hz and 100 kHz for the wet and the dry nail. The results of this study indicate that the dielectric spectroscopy may be useful in observing the decomposition of water in the diabetic nail plate.

Implications of the alpha dispersion for studies on interaction of tobacco smoke--corneal tissue.

In this work, we have carried out a dielectric study to determine the effect of tobacco smoke on the rat corneal function. Measurements were performed over the frequency range of 500 Hz-100 kHz in air and at the temperature of 35°C. The frequency dependencies of the loss tangent for both healthy and smoky cornea exhibit two peaks with different width occurring as a narrow at 2 kHz and a broad at around 16 kHz. The distribution parameter α at 2 kHz has a value of about 0.3, which increases to 0.6 at 16 kHz. The magnitude of the permittivity decrement at 2 and 16 kHz is about two and four times higher, respectively, for the smoky cornea than that for the healthy one. These dielectric studies indicate that the present method is useful in detection of the effect of tobacco smoke exposure on the corneal behavior.

Diabetes mellitus effect on rat corneal dielectric properties.

In the course of the study, we carried out a dielectric examination to determine the effect of diabetes mellitus on the rat corneal function. Measurements were performed over the frequency range of 500 Hz-100 kHz in air and at the temperatures from 25 to 150°C. The frequency dependencies of the loss tangent for the healthy and the diabetic cornea exhibit two peaks at 2 kHz and 16 kHz in the α-dispersion region. The amplitude of these both peaks is smaller for the diabetic cornea than that for the healthy one. The temperature dependencies of the loss tangent for the healthy and the diabetic cornea reveal ß-relaxation in the range of 30-70°C and 50-90°C, respectively. The present study exhibits that the dielectric spectroscopy is useful in detection of the effect of diabetes mellitus on the corneal molecular behavior.

Dielectric studies of the paracetamol-lenticular tissue interactions.

This paper reports on the effect of paracetamol on the dielectric behavior of the rabbit lens. Measurements were performed over the frequency range of 100 Hz-100 kHz in air and at the temperature of 35°C. The frequency dependencies of the relative permittivity and dielectric loss for the control and paracetamol-control lenses are described in terms of a power-low, Debye and Cole-Cole relations. The effect of paracetamol on the dielectric properties of the lens is visible in the lower values of the relative permittivity than those for the control sample at the same frequency. In addition, the relaxations around 18 and 46 kHz for the paracetamol-control lens are shifted to lower frequencies compared with the control lens. The results of this work indicate that the present method is useful in detection of the lens toxicity elicited by overdoses of paracetamol in animal.

Molecular interactions in human nail plate analysed by dielectric spectroscopy.

The influence of diabetes mellitus on dielectric properties of the human fingernail was measured in vitro in the alpha-dispersion region. The frequency dependencies of the permittivity and conductivity for the healthy and the diabetic nail plate revealed three separate relaxations, which were similar for both materials. Significant differences were observed in the values of permittivity at the same frequency between the healthy and the diabetic nails with low water content of about 0% and 3%. Results of this paper suggest that hyperglycemia alters the first-order structure of the nail keratin macromolecule.