Effects of blood storage on rheology and damage in low-stress shear flow

Data are presented on the rheological and hemolytic behavior of whole human blood as it ages while stored at 4 degrees C (as in blood banking practice) up to 26 days. The viscometric properties of steady shear viscosity eta and oscillatory (complex) viscosity eta * = eta' - i eta" reported over ranges of shear rate gamma and radian frequency omega of 33 less than gamma less than 4130 s-1 and 1.5 less than omega less than 48 s -1; data on autologous plasma are given for reference. The Cox-Merz relation, eta (gamma) = [eta *(omega)] omega = gamma, is found to be a good approximation, with eta greater than or equal to [eta *], over the range studied. Release of hemoglobin (Hgb) and lactate dehydrogenase (LDH) into the plasma during shearing is tracked as a function of time for 30 min, and its sensitivity to gamma magnitude is measured. Bloods from four different donors are studied, with primary attention given to one (SSR). For all bloods, the release of both Hgb and LDH increases with storage age, but differences in such aging characteristics between different bloods can be substantial (even when rheological properties are identical). A post-shear incubation at 4 degrees C for one day shows no enhancement of plasma Hgb and LDH levels beyond those expected from normal aging after the shearing experience, demonstrating the absence of significant delayed-action effects as a consequence of shearing trauma.     

Extracellular microbial polysaccharides: Generalized power law for biopolysaccharide solutions

A generalized power low model, \documentclass{article}\pagestyle{empty}\begin{document}$ \eta \, = \,\eta _0 [1\, + \,(\dot \gamma /\gamma _0 )];{N - 1} $\end{document}, is shown to described satisfactorily the shear viscosity data for xanthan gum solutions from 0.18 g/L to nearly 4 g/L and low to intermediate shear rates. Since mixing, mass and heat transfer, residence time distributions, and power input for agitation and aeration all depend on shear viscosity, this equation provides a simple prediction of this important quantity over the shear rate ranges characteristic of fermentations.     

Numerical simulation on the biomechanical interactions of tooth/implant-supported system under various occlusal forces with rigid/non-rigid connections

The aim of this study was to analyze the biomechanics in an implant/tooth-supported system under different occlusal forces with rigid/non-rigid connectors by adopting a 3D non-linear finite element (FE) approach. A 3D FE model containing one Frialit-2 implant splinted to the mandibular second premolar was constructed. Contact elements (frictional surface) were used to simulate the realistic interface condition within the implant system and the sliding keyway stress-breaker function. The stress distributions in the splinting system and dissimilar mobility between natural tooth and implant with rigid and non-rigid connectors were observed for six loading types. The simulated results indicated that the lateral occlusal forces significantly increased the implant (sigma(I, max)), alveolar bone (sigma(AB, max)) and prosthesis (sigma(P, max)) stress values when compared with the axial occlusal forces. The sigma(I, max) and sigma(AB, max) values did not exhibit significant differences regardless of the connector type used. However, the sigma(P, max) values with a non-rigid connection increased more than two times those of the rigid connection. The sigma(I, max), sigma(AB, max) and sigma(P, max) stress values were significantly reduced in centric or lateral contact situations once the occlusal forces on the pontic were decreased. Moreover, the vertical-tooth-to-implant displacement ratios with a non-rigid connection were 23 and 9.9 times that for axial and lateral loads, respectively, applied on the premolar. However, the compensated non-rigid connector capabilities were not significant when occlusal forces acted on the complete prosthesis. The non-rigid connector (keyway device) only significantly exploited its function when the occlusal forces acted on a natural tooth. Minimizing the occlusal loading force on the pontic area through occlusal adjustment procedures to redistribute stress in the maximum intercuspation or lateral working position for an implant/tooth-supported prosthesis is recommended.     

Viscoelastic properties of solutions of ovine submaxillary mucin

The linear viscoelastic and rheological properties of high molecular weight ovine submaxillary mucin (OSM) solution have been investigated in terms of the Newtonian steady-flow viscosity [eta(gamma)], the complex oscillatory viscosity [eta*(omega)], and the storage and loss shear moduli [G'(omega) and G"(omega)]. It was observed that tau(gamma), eta*(omega), and G'(omega) are always higher when OSM is dissolved in 0.1M NaCl than when at the same concentration in 6M GdnHCl. This is consistent with previous observations that submaxillary mucins self-associate in 0.1M NaCl to form large aggregates, which are disrupted in 6M GdnHCl. As the OSM concentration increases, the appearance of a plateau shear modulus indicates the formation of a gel network in both solvents. The results suggest gelation involves specific intermolecular interactions, perhaps due to hydrophobic forces between interdigitated oligosaccharide side chains. The viscoelastic behavior of OSM solution at high concentration is thus similar to that reported in the literature for porcine gastric mucin (PGM). However, the OSM gels are mechanically weaker, having moduli that are an order of magnitude lower than those for PGM gels of comparable concentration. The oligosaccharide side chains of OSM consist of only 1-2 sugar units compared to 10-15 for PGM, but it appears that this is sufficient to allow for intermolecular interaction and the formation of weak gels.     

Viscoelastic and rheological properties of concentrated solutions of proteoglycan subunit and proteoglycan aggregate

The oscillatory and steady shear rheological properties of concentrated solutions of proteoglycan subunit (PGS) and aggregate (PGA) from bovine articular cartilage have been studied using a Rheometrics fluids spectrometer. At comparable concentrations in the physiological range tan delta increases from 0.5 to 1.0 for PGA as the oscillation frequency (omega) increases from 10(-1) to 10(2) rads/s, compared to a decrease from 40 to 5 for PGS. Thus PGA solutions exhibit predominantly elastic response whereas those of PGS exhibit primarily viscous behavior. PGA solutions show pronounced shear-thinning behavior at all shear rates (gamma) in the range 10(-2) less than gamma (s-1) less than 10(2), whereas PGS solutions exhibit predominantly Newtonian flow. For PGA, the small-strain complex viscosity eta* (omega) is substantially smaller than the steady-flow viscosity eta(gamma) at comparable values of omega and gamma. These observations indicate that the presence of proteoglycan aggregates leads to formation of a transient or weak-gel network. Since aggregation leads to a large increase in molecular hydrodynamic volume and hence in the relaxation times for macromolecular rotation, it appears that role of aggregate formation is to shift the linear viscoelastic response from the terminal viscous flow into the plateau elastomeric regime of relaxational behavior. Normal or pathological changes that produce a decrease in aggregation will result in a loss of elastomeric behavior of the proteoglycan matrix.     

Correlation between the association and the desmutagenicity of benzo(a)pyrene by hemin: comparison with hemoproteins, transient metals and amines

The mutagenicity of the potent carcinogen benzo(a)pyrene proved to be lost by binding with hemin and other tested compounds. The association constant (Kass) and the desmutation constant (Kmut) of benzo(a)pyrene and hemin were 8.5 x 10(4) M(-1) and 7.0 x 10(-4) M(-1), respectively. The correlation coefficient (gamma) of the association and the desmutation of benzo(a)pyrene and hemin was nearly 1, and the coefficient of regression of association on the desmutation, gamma (sigma ass/sigma mut), was 0.78. The correlation of other compounds, ferric chloride among transient metals, and 3,3'-diaminodipropylamine and p-phenylenediamine, were also almost 1 in both values, but their Kass an Kmut were must smaller than those of hemin: Kass:Kmut, 525 M(-1):520 M(-1) for ferric chloride, 2.2 x 10(3) M(-1):2.3 x 10(3) M(-1) for diaminodipropylamine and 175 M(-1):125 M(-1) for p-phenylenediamine. Good agreement of Kass and Kmut means that the desmutation of benzo(a)pyrene is caused by binding with tested materials.     

Thermal excitations of a bilipid membrane.

Propagating modes of vibration of a bilipid membrane have been detected with light beating spectroscopy. The dependence of omega on q is consistent with a model of a fluid film of surface tension sigma = 2.5 +/- 0.5 dyn cm-1 surrounded by a medium with rho = 1 g cm-3 and eta = 1.01 X 10(-2) P.     

Mapping of fluorescence anisotropy in living cells by ratio imaging. Application to cytoplasmic viscosity.

Steady-state and time-resolved fluorescence properties of probes incorporated into living cells give information about the microenvironment near the probe. We have extended studies of spatially averaged fluorescence anisotropy (r) by using an epifluorescence microscope, equipped with excitation and emission polarizers and an image analysis system, to map r of nonoriented fluorophores incorporated into cultured cells. With this imaging system, r for reflected light or glycogen scattering solutions was greater than 0.98. Measurement of r over the range 0.01-0.35 for fluorophores in bulk solution and in thin capillary tubes placed side-by-side gave values equivalent to r measured by cuvette fluorometry. Cytoplasmic viscosity (eta) in Madin-Darby canine kidney (MDCK) cells and Swiss 3T3 fibroblasts was examined from anisotropy images and time-resolved fluorescence decay of the cytoplasmic probes 2,7-bis-carboxyethyl-5 (and 6)-carboxy-fluorescein (BCECF) and indo-1. Nanosecond lifetimes and anisotropy decay were measured using a pulsed light source and gated detector interfaced to the epifluorescence microscope. Anisotropy images of BCECF in MDCK cells revealed two distinct regions of r: one from the cytoplasm (r = 0.144 +/- 0.008) and a second appearing at late times from the interstitial region (r = 0.08 +/- 0.03), representing BCECF trapped beneath the tight junctions. Anisotropy values, taken together with intracellular life-times and the calibration between r and eta/tau f for water/glycerol mixtures, gave eta values of 10-13 cP at 23 degrees C. These values assume little fluorophore binding to intracellular components and are therefore upper limits to cytoplasmic viscosity. These data establish a new methodology to map anisotropy in intact cells to examine the role of fluidity in cellular physiology.     

The tuberous sclerosis gene products hamartin and tuberin are multifunctional proteins with a wide spectrum of interacting partners

Mutations in the tumor suppressor genes TSC1 and TSC2, encoding hamartin and tuberin, respectively, cause the tumor syndrome tuberous sclerosis with similar phenotypes. Until now, over 50 proteins have been demonstrated to interact with hamartin and/or tuberin. Besides tuberin, the proteins DOCK7, ezrin/radixin/moesin, FIP200, IKKbeta, Melted, Merlin, NADE(p75NTR), NF-L, Plk1 and TBC7 have been found to interact with hamartin. Whereas Plk1 and TBC7 have been demonstrated not to bind to tuberin, for all the other hamartin-interacting proteins the question, whether they can also bind to tuberin, has not been studied. Tuberin interacts with 14-3-3 beta,epsilon,gamma,eta,sigma,tau,zeta, Akt, AMPK, CaM, CRB3/PATJ, cyclin A, cyclins D1, D2, D3, Dsh, ERalpha, Erk, FoxO1, HERC1, HPV16 E6, HSCP-70, HSP70-1, MK2, NEK1, p27KIP1, Pam, PC1, PP2Ac, Rabaptin-5, Rheb, RxRalpha/VDR and SMAD2/3. 14-3-3 beta,epsilon,gamma,eta,sigma,tau,zeta, Akt, Dsh, FoxO1, HERC1, p27KIP1 and PP2Ac are known not to bind to hamartin. For the other tuberin-interacting proteins this question remains elusive. The proteins axin, Cdk1, cyclin B1, GADD34, GSK3, mTOR and RSK1 have been found to co-immunoprecipitate with both, hamartin and tuberin. The kinases Cdk1 and IKKbeta phosphorylate hamartin, Erk, Akt, MK2, AMPK and RSK1 phosphorylate tuberin, and GSK3 phosphorylates both, hamartin and tuberin. This detailed summary of protein interactions allows new insights into their relevance for the wide variety of different functions of hamartin and tuberin.     

Distensibility characteristics of caval veins and empirical exponential formulae

The stress-strain curves of the vena cava have been measured of vena cava superior, and the intrathoracic and abdominal portions of vena cava inferior excised from dogs. The stress sigma is expressed by the exponential function of the strain gamma as follows: sigma = sigma 0[exp (gamma/gamma 0) - 1] in the longitudinal direction, and sigma = sigma 1[exp(gamma/gamma 1) - 1] + sigma 2 [exp(gamma/gamma 2) - 1] in the circumferential one for all the three kinds of veins. The constants sigma 0, gamma 0, sigma 1, gamma 1, sigma 2 and gamma 2 are determined by a nonlinear least squares method.     

Solution properties of the galactomannans extracted from the seeds of Caesalpinia pulcherrima and Cassia javanica: comparison with locust bean gum.

The galactomannans from the seeds of Caesalpinia pulcherrima and Cassia javanica were extracted from the milled seeds in water at room temperature. Both products, as well as a commercial sample of locust bean gum (LBG), were purified by precipitation in isopropyl alcohol. The intrinsic viscosity determined for LBG, [eta] = 15.2 dl/g, was slightly higher than those for the other two galactomannans. The dependence of the specific viscosity at zero shear rate on the coil overlap parameter, C[eta], revealed a similar behaviour for the three galactomannans. A master curve was obtained with a critical concentration, C*, at C*[eta] = 3.3. The slope of the curve in the concentrated regime is higher than the values in the range of 3.9-6.6, obtained for the generalized behaviour of several random coil polysaccharides. Dynamic experiments showed that, at the concentrations studied, the behaviour of the galactomannans was typical of systems with predominant entanglement networks in the region between the terminal and plateau zones of frequency response. The correlation between dynamic and steady shear properties (Cox Merz rule) was satisfactory for the three galactomannans.     

Role of hydrogen bonding in red cell aggregation.

The role of hydrogen bonding in red cell aggregation induced by dextran was studied with the use of urea, an inhibitor for hydrogen bonding. In order to avoid hemolysis of red cells by the high concentration of urea, the studies were performed on human red cells hardened in glutaraldehyde. The degree of red cell aggregation at Hct = 45% was estimated by the use of a coaxial cylinder viscometer. The viscometric aggregation index (VAI) was calculated from viscosity values at shear rates of 52 sec-1 (eta H) and 0.05 sec-1 (eta L); VAI = (eta L - eta H)/eta H. Red cells with surface charge intact and with charge removal by neuraminidase treatment were studied. Urea at high concentrations, e.g., 6 M, significantly inhibited red cell aggregation induced by dextran. These findings indicate that hydrogen bonding plays an important role in dextran-induced red cell aggregation. An understanding of the nature of the forces involved in red cell aggregation serves to establish the physicochemical principles of cell-to-cell interactions induced by macromolecules.     

Surfactant-spreading and surface-compression disturbance on a thin viscous film

Spreading of a new surfactant in the presence of a pre-existing surfactant distribution is investigated both experimentally and theoretically for a thin viscous substrate. The experiments are designed to provide a better understanding of the fundamental interfacial and fluid dynamics for spreading of surfactants instilled into the lung. Quantitative measurements of spreading rates were conducted using a fluorescent new surfactant that was excited by argon laser light as it spread on an air-glycerin interface in a petri dish. It is found that pre-existing surfactant impedes surfactant spreading. However, fluorescent microspheres used as surface markers show that pre-existing surfactant facilitates the propagation of a surface-compression disturbance, which travels faster than the leading edge of the new surfactant. The experimental results compare well with the theory developed using lubrication approximations. An effective diffusivity of the thin film system is found to be Deff = (E*gamma)/(mu/H), which indicates that the surface-compression disturbance propagates faster for larger background surfactant concentration, gamma, larger constant slope of the sigma*-gamma* relation, -E*, and smaller viscous resistance, mu/H. Note that sigma* and gamma* are the dimensional surface tension and concentration, respectively, mu is fluid viscosity, and H is the unperturbed film thickness.     

Effects of viscoelasticity of cytoplasm on the complex viscosity of red blood cell suspensions

To consider the effects of the viscoelasticity of cytoplasm on the relaxation phenomenon of red blood cell suspensions, we calculate the complex intrinsic viscosity [eta*] = lim(eta* - eta)/eta c of the disperse system of spherical c----0 cells as a function of the frequency, where eta* is the complex viscosity in suspensions, eta the medium viscosity and c the volume concentration of the cells. The cell consists of a viscoelastic membrane and a viscoelastic cytoplasm. The viscoelasticity of the membrane is described by the Voigt model, while the viscoelasticity of the cytoplasmic region is described either by the Maxwell model or by the Voigt model. The interfacial tension is taken into account on both the interfaces of the membrane. The results of [eta*] are compared with the ones in the case in which the cytoplasmic region is purely viscous liquid.     

Identification of different isoforms of 14-3-3 protein family in human dermal and epidermal layers

We have previously demonstrated a high level of stratifin, also known as 14-3-3 sigma in differentiated keratinocyte cell lysate and conditioned medium (CM). In this study, we asked the question of whether other 14-3-3 isoforms are expressed in human dermal fibroblasts, keratinocytes, intact dermal and epidermal layers of skin. In order to address this question, total proteins extracted from cultured cells or skin layers were subjected to western blot analysis using seven different primary antibodies specific to well-known mammalian isoforms, beta, gamma, epsilon, eta, sigma, tau, and zeta of 14-3-3 protein family. The autoradiograms corresponding to each isoform were then quantified and compared. The results revealed the presence of very high levels of all seven isoforms in cultured keratinocyte and conditioned medium. With the exception of tau isoform, other 14-3-3 isoforms were also present in intact epidermal layer of normal skin. The profile of 14-3-3 proteins in whole skin was similar to that of epidermis. In contrast, only gamma 14-3-3 isoform, was present in dermal layer obtained from the same skin sample. On the other hand, cultured fibroblasts express a high level of beta, epsilon, gamma and eta and a low level of zeta and tau, but not sigma isoform. However, the levels of 14-3-3 epsilon, gamma and eta were barely detectable in fibroblast conditioned medium. Further, we also used immunohistochemical staining to identify the 14-3-3 isoform expressing cells in human skin sections. The finding revealed different expression profile for each of these isoforms mainly in differentiated keratinocytes located within the layer of lucidum. However, fibroblasts located within the dermal layer did not show any detectable levels of these proteins. In conclusion, all members of 14-3-3 proteins are expressed by cells of epidermal but not dermal layer of skins and that these proteins are mainly expressed by differentiated keratinocytes.     

Structural studies of agar-gelatin complex coacervates by small angle neutron scattering, rheology and differential scanning calorimetry

Agar-gelatin complex coacervates are studied by small angle neutron scattering (SANS), rheology (in both flow and temperature scan modes) and differential scanning calorimetry (DSC) in order to probe the microscopic structure of this dense protein-polysaccharide-rich phase. DSC and isochronal temperature sweep (rheology) experiments yielded a characteristic temperature at approximately 35+/-2 degrees C. Rheology data revealed a second characteristic temperature at approximately 75+/-5 degrees C which was absent in DSC thermograms. In the flow mode, shear viscosity (eta) was found to scale with (Carreau model) applied shear rate (gamma ) as: eta(gamma ) approximately (gamma )(-k) with k=1.2+/-0.2 indicating non-Newtonian and shear-thinning features independent of ionic strength. The static structure factor S(q) deduced from SANS data in the low wave vector (0.018 A(-1)相似文献   

Surface forces in lungs. II. Microstructural mechanics and lung stability

Recent lung microstructural models describing interactions between alveolar surface tension (gamma) and forces in structural elements of the alveolar duct predict that the component of lung recoil pressure due to gamma (P gamma) is proportional to gamma/V1/3, where V is the total lung volume. This relation is tested against experimental data obtained from pressure-volume measurements of excised rabbit lungs with different constant values of gamma. It is found that for values of gamma less than approximately 18 dyn/cm the data generally agree with the model predictions. With higher values of gamma, a mismatch between the data and predictions first occurs at low and high volumes and then spreads over the entire volume range. The mismatch at the lower volumes coincides with the appearance of nonuniformities of lung expansion. The nonuniformities are characterized by a coexistence of under- and overexpanded regions of the parenchyma referred to as a mixture of phases. These nonuniformities, as well as a pressure-volume curve with a shape similar to the shape of measured curves, are predicted from an analysis of lung stability. Results of this work indicate that if the lung expands uniformly, P gamma proportional to gamma/V1/3 is a good approximation over a wide range of volumes. The stability analysis indicates that the equilibrium configurations of the lung parenchyma when gamma is independent of interfacial area and elevated above normal values are nonuniform states of expansion, characterizable as a mixture of phases. This result confirms that a dependence of gamma on surface area is normally required to achieve stable, uniform states of lung expansion.     

Toxoplasma gondii: effect of infection on expression of 14-3-3 proteins in human epithelial cells

14-3-3 Proteins are expressed in most eukaryotes organisms and play varied and crucial roles in a wide range of regulatory processes. In mammalian cells, seven 14-3-3 isoforms have been identified. However, it is not known what effect infection has on 14-3-3 isoform expression. In this study human colonic carcinoma cell lines were infected with Toxoplasma gondii for 24h and expression of 14-3-3 proteins was determined by RT-PCR. HT-29 cells only expressed 3 out of the 7 isoforms while 5 and all 7 isoforms were found in HCT-116 and Caco-2 cells, respectively. Infection had little or no effect in the expression of 14-3-3gamma, epsilon, sigma, and xi; but in HCT-116 cells induced expression of 14-3-3eta and sigma, while 14-3-3beta, eta, and xi were induced in HT-29 cells. If 14-3-3 proteins are involved in cell survival and/or prevention of parasite replication, longer incubation times may be required as no differences in percentage of infection were found among the cell lines at 24h post-infection.