The dynamic mechanical, dielectric, and melting behavior of reconstituted collagen

Effect of water on the molecular mobility of elastin

Purified and hydrated elastin is studied by both thermal and dielectric techniques to have insight into the chain dynamics of this protein. By differential scanning calorimetry, the glassy behavior of elastin is highlighted; the glass transition temperature (T(g)) of elastin is found to be widely dependent on hydration, falling from 200 degrees C in the dehydrated state to 30 degrees C for 30% hydration. A limit of T(g) at around 0 degrees C is found when crystallizable water is present in the system, that is, when the formation of ice prevents motions of some 10 nm along the polypeptidic chains. The technique of thermally stimulated currents, carried out in the -180 to 0 degrees C temperature range, is useful to detect localized motions. In this case, too, the localized motions vary considerably according to hydration: a first relaxation mode is observed at -145 degrees C and it is associated with the reorientation of crystallizable water in ice I; a second relaxation mode, more complex and cooperative, occurs at around -80 degrees C and could be attributed to the complex constituted by the dipolar groups of the polypeptidic chain and noncrystallizable water, behaving as a glassy system.

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

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 gamma-radiation changes the electrical and thermal properties of the bone. Electrical conductivity (sigma) of the bone decreases with consecutive heating runs. The decrease in sigma 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.

Temporary Changes in the dc ElectricalConductivity of MX (3-Chloro-4(Dichloromethyl)-5-Hydroxy-2(5H)-Furanone) Treated Collagen

The influence of MX(3-Chloro-4(Dichloromethyl)-5-Hydroxy-2(5H)- Furanone), a stronglymutagenic compound, on the temperature dependence of the dcelectrical conductivity of collagen as a function of time was studied.Collagen was immersed in MX solution, next dried and pressed intotablets. The MX concentration was measured by HPLC analysis.The reduction of MX concentration to 10% of the initial value wasobserved in the presence of collagen in the solution, whereas in thecontrol solution concentration of MX decreased to 70% of the initialvalue. Measurements of electrical conductivity were performed for thetemperature range 295-453K and activation energies for the chargeconduction process were calculated. Within the temperature range295-340K, the presence of MX decreased electrical conductivity ofcollagen. Calculated activation energies were typical for dry proteins.Within the temperature range 295-320K activation energy decreasedwith time, probably due to the stronger interactions in thecollagen-water-MX system. For temperatures between 320-410 and430-450K the activation energy was not time dependent and theapplication of MX did not change the structure of the collagenmacromolecule. The temporary changes occurring at the lowertemperatures being due solely to changes in the collagen-waterinteractions.

Dielectric characterization of collagen, elastin, and aortic valves in the low temperature range

The low temperature dielectric relaxation of porcine aortic valves and its main macromolecular proteins. i.e. elastin and collagen, have been investigated in the dry state and at low levels of hydration by thermally stimulated currents spectrometry, with an equivalent frequency of 10(-3) Hz. Two secondary relaxation modes, labeled gamma and beta with increasing temperature, are found for the three materials. Since the gamma-mode is independent upon hydration while the beta-mode is strongly plasticized by water, these relaxation modes have been attributed to localized motions of the polypeptidic chains containing apolar and polar residues, respectively. The deconvolution of the beta-mode by fractional polarization gives the experimental distribution of the dielectric relaxation times of the three materials, and allows us to deduce the activation parameters of each elementary process. These analyses shows the existence of compensation phenomena between the activation parameters, implying cooperative mechanisms. The occurrence of these phenomena with their characteristic parameters are used to specify the origin of the localized relaxation modes in collagen and elastin, and to assign the specific role of each protein in the aortic valves.

The effect of gamma-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.

Stress-strain curve and Young's modulus of a collagen molecule as determined by the X-ray diffraction technique

The purpose of the work described in this paper was to make a stress-strain curve for a collagen molecule and estimate Young's modulus of a molecule along the molecular axis. X-ray diffractometry was performed on bovine Achilles tendon in order to measure strain in the collagen molecule along the molecular axis as a response to a macroscopically applied force. By geometrical calculations and experiments, cross-sectional areas of a molecule and molecules in a tendon collagen fiber were determined. The applied force was translated to the stress and the stress-strain curve of the collagen molecule was constructed, which was found to be almost linear. Young's modulus of the molecule was determined to be slightly smaller than when determined by dynamic mechanical methods. The difference was considered to suggest the existence of a viscoelastic component within the molecule as well as the difference in the mechanical properties of collagen in different tissues. The expected viscoelasticity was speculated to be related to the hydrogen bond network in the collagen molecule.

Viscoelastic and thermal properties of collagen/poly(vinyl alcohol) blends

Blends of poly(vinyl alcohol) (PVA) with collagen and gelatin, prepared from aqueous solution by solvent casting, were investigated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). After conditioning at 51% relative humidity, collagen and PVA show nearly coincident glass transition temperatures (Tg approximately 35 degrees C), while gelatin has a higher Tg (approximately 70 degrees C). Gelatin/PVA blends show two invariant Tgs, whose temperature and associated specific heat increment clearly indicate the coexistence of two amorphous phases composed of the pure components. Owing to similarity of the Tgs of collagen and PVA after humidity conditioning, DSC offers no indication on miscibility of collagen/PVA blends. In DMTA experiments, where absorbed water freely evaporates from the samples during the thermal scan, PVA shows a glass transition relaxation at about 50 degrees C, while both gelatin and collagen display an intense glass transition in the vicinity of 230 degrees C. The DMTA spectra of collagen/PVA and gelatin/PVA blends show two invariant glass transition relaxations at about 50 and 230 degrees C. Absence of any Tg shift with composition demonstrates that the blend components are immiscible. However, blends of PVA with collagen and gelatin form optically clear films with good mechanical properties over the whole range of compositions. It is found that at T > Tg (PVA) the elastic modulus (E') of the blends strongly increases with increasing content of the biopolymer. In the case of collagen/PVA blends, experimental E' values agree with the predictions of a simple two-phase composite model with phases connected in parallel. It is concluded that, though thermodynamically immiscible with both native and denatured collagen, PVA forms mechanically compatible blends with collagen and gelatin.

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.

Influence of cadmium on the chain dynamics of collagen in rat tail tendon

The molecular mobility of the chain dynamics of collagen was investigated by the thermally stimulated creep method on rat tail tendon after oral administration of cadmium (8 mg.kg-1.day-1) for six weeks. The high resolving power of the technique shows two manifestations of the pseudolathyrogen effect of cadmium: the polar side-chains of collagen, mobile in the immature specimen, which are cross-linked and so immobile in the mature specimen, remain mobile in the cadmium-treated mature specimen. There is also a subsequent decrease in the number of water molecules linked by two hydrogen atoms bound to the tropocollagen molecules. Probably these molecular modifications inhibit mineralization of the organic matrix and so osteogenesis.

Analysis of the effects of pH and tensile deformation on the small-deformation modulus of calf skin

A dynamic technique was used to measure the elastic modulus of the reticular dermis of calf skin at a small (0.1%), non-perturbing oscillating deformation. The elastic modulus increases by over an order of magnitude when the tissue is stretched by only 10% before the measurement is made. The results are interpreted by a stochastic model of fiber orientation that includes the orientation of fibers and their straightening out from slack configurations into the load-bearing structure. An equation is derived that accurately describes the course of the modulus-extension curve over a range of pH from 3 to 11, and allows the calculations of the properties and configurations of the slack fibers. One of these is the Young's modulus of a fiber, which agrees well with the previous determinations in neutral medium.