Viscoelastic characteristics of protein solutions and the micromechanics of their motion in porous carriers

The interactions of model proteins with porous matrices in biosensors are considered. The viscoelastic properties of casein and albumin were assessed by a dynamic method of a piezoquartz resonator by applying thin layers of the studied solutions to a piezocrystal. The experimental data on the viscoelastic characteristics of protein solutions of various concentrations were compared with the characteristics of their tangential motion in the porous carriers of cellulose nitrate. It was demonstrated that the parameters of dynamic viscosity correlated with the motion time of the protein solutions in the porous polymeric carrier.     

Fluid transport and mechanical properties of articular cartilage: a review

This review is aimed at unifying our understanding of cartilage viscoelastic properties in compression, in particular the role of compression-dependent permeability in controlling interstitial fluid flow and its contribution to the observed viscoelastic effects. During the previous decade, it was shown that compression causes the permeability of cartilage to drop in a functional manner described by k = ko exp (epsilon M) where ko and M were defined as intrinsic permeability parameters and epsilon is the dilatation of the solid matrix (epsilon = tr delta u). Since permeability is inversely related to the diffusive drag coefficient of relative fluid motion with respect to the porous solid matrix, the measured load-deformation response of the tissue must therefore also depend on the non-linearly permeable nature of the tissue. We have summarized in this review our understanding of this non-linear phenomenon. This understanding of these flow-dependent viscoelastic effects are put into the historical perspective of a comprehensive literature review of earlier attempts to model the compressive viscoelastic properties of articular cartilage.     

The viscoelastic properties of actin solutions

The viscoelastic properties in actin solutions were investigated by measuring their elastic modulus and viscous modulus using a rheometer. The polymerization/gelation process of actin solutions was accompanied by an increase of both parameters, indicating the formation of a protein network. High shear rotational motion destroyed this network which, however, would reanneal if left undisturbed. At 25 °C under low ionic strength conditions, the viscoelastic moduli of a Spudich-Watt globular (G) actin preparation increased with time, while G-actin, purified by gel filtration maintained low viscoelastic moduli. The rigidity of the filamentous (F) actin network in a solution of Spudich-Watt actin, measured by the elastic modulus, was somewhat lower than that of gel-filtration-purified actin at the same protein concentration. The crosslink density of these F-actin networks was estimated, using models from rubber elasticity theory. The calculated density was 1 crosslink/50 actin monomers for the purified actin and 1 crosslink/120 actin monomers for Spudich-Watt actin. The results are consistent with the idea that a small amount of regulatory factor(s), which could be removed by the gel filtration step, modulates the structure of an actin network.     

A new method for measuring viscoelasticity of liquids by means of fluorescence spectroscopy

The Brownian motion of a spherical particle in a generalized viscoelastic medium is discussed to obtain the complex viscosity coefficient from the photocurrent correlation function of fluorescent light radiated from the particle. This method makes it possible to measure the viscoelastic properties of a small amount of solution sample.     

The effect of blood viscoelasticity on pulsatile flow in stationary and axially moving tubes

An analytical solution for pulsatile flow of a generalized Maxwell fluid in straight rigid tubes, with and without axial vessel motion, has been used to calculate the effect of blood viscoelasticity on velocity profiles and shear stress in flows representative of those in the large arteries. Measured bulk flow rate Q waveforms were used as starting points in the calculations for the aorta and femoral arteries, from which axial pressure gradient ▿P waves were derived that would reproduce the starting Q waves for viscoelastic flow. The ▿P waves were then used to calculate velocity profiles for both viscoelastic and purely viscous flow. For the coronary artery, published ▿P and axial vessel acceleration waveforms were used in a similar procedure to determine the separate and combined influences of viscoelasticity and vessel motion.Differences in local velocities, comparing viscous flow to viscoelastic flow, were in all cases less than about 2% of the peak local velocity. Differences in peak wall shear stress were less than about 3%.In the coronary artery, wall shear stress differences between viscous and viscoelastic flow were small, regardless of whether axial vessel motion was included. The shape of the wall shear stress waveform and its difference, however, changed dramatically between the stationary and moving vessel cases. The peaks in wall shear stress difference corresponded with large temporal gradients in the combined driving force for the flow.     

Stress-sensitive tissue regeneration in viscoelastic biomaterials subjected to modulated tensile strain

This research contribution addresses the mechanochemistry of intra-tissue mass transfer for nutrients, oxygen, growth factors, and other essential ingredients that anchorage-dependent cells require for successful proliferation on biocompatible surfaces. The unsteady state reaction-diffusion equation (i.e., modified diffusion equation) is solved according to the von Kármán-Pohlhausen integral method of boundary layer analysis when nutrient consumption and tissue regeneration are stimulated by harmonically imposed stress. The mass balance with diffusion and stress-sensitive kinetics represents a rare example where the Damköhler and Deborah numbers appear together in an effort to simulate the development of mass transfer boundary layers in porous viscoelastic biomaterials. The Boltzmann superposition integral is employed to calculate time-dependent strain in terms of the real and imaginary components of dynamic compliance for viscoelastic solids that transmit harmonic excitation to anchorage-dependent cells. Rates of nutrient consumption under stress-free conditions are described by third-order kinetics which include local mass densities of nutrients, oxygen, and attached cells that maintain dynamic equilibrium with active protein sites in the porous matrix. Thinner nutrient mass transfer boundary layers are stabilized at shorter dimensionless diffusion times when the stress-free intra-tissue Damköhler number increases above its initial-condition-sensitive critical value. The critical stress-sensitive intra-tissue Damköhler number, above which it is necessary to consider the effect of harmonic strain on nutrient consumption and tissue regeneration, is proportional to the Deborah number and corresponds to a larger fraction of the stress-free intra-tissue Damköhler number in rigid biomaterials.     

Material characterization of porcine lenticular soluble proteins

The soluble proteins present in the ocular lens impart important optical and dynamic mechanical properties on the lens. The short-range order of crystallin proteins grants transparency to a very concentrated protein solution. This unique protein system directly enables proper visual function of the eye. These proteins were investigated in steady and oscillatory shear. Steady shear data were fitted with a modified Herschel-Bulkley yield stress model that allows for a Newtonian plateau at low shear rates. The Cox-Merz rule was used in conjunction with large amplitude oscillatory shear to give insight into the degradation of the fluid structure with increasing strain. The shear thinning viscoelastic behavior of these proteins gives rise to beneficial mechanical properties and results from the same short-range order granting optical transparency.     

Dynamic cell culture on porous biopolymer microcarriers in a spinner flask for bone tissue engineering: a feasibility study

Porous microspherical carriers have great promise for cell culture and tissue engineering. Dynamic cultures enable more uniform cell population and effective differentiation than static cultures. Here we applied dynamic spinner flask culture for the loading and multiplication of cells onto porous biopolymer microcarriers. The abilities of the microcarriers to populate cells and to induce osteogenic differentiation were examined and the feasibility of in vivo delivery of the constructs was addressed. Over time, the porous microcarriers enabled cell adhesion and expansion under proper dynamic culture conditions. Osteogenic markers were substantially expressed by the dynamic cell cultures. The cell-cultured microcarriers implanted in the mouse subcutaneous tissue for 4 weeks showed excellent tissue compatibility, with minimal inflammatory signs and significant induction of bone tissues. This first report on dynamic culture of porous biopolymer microcarriers providing an effective tool for bone tissue engineering.     

Hydromagnetic Flow and Heat Transfer over a Porous Oscillating Stretching Surface in a Viscoelastic Fluid with Porous Medium

An analysis is carried out to study the heat transfer in unsteady two-dimensional boundary layer flow of a magnetohydrodynamics (MHD) second grade fluid over a porous oscillating stretching surface embedded in porous medium. The flow is induced due to infinite elastic sheet which is stretched periodically. With the help of dimensionless variables, the governing flow equations are reduced to a system of non-linear partial differential equations. This system has been solved numerically using the finite difference scheme, in which a coordinate transformation is used to transform the semi-infinite physical space to a bounded computational domain. The influence of the involved parameters on the flow, the temperature distribution, the skin-friction coefficient and the local Nusselt number is shown and discussed in detail. The study reveals that an oscillatory sheet embedded in a fluid-saturated porous medium generates oscillatory motion in the fluid. The amplitude and phase of oscillations depends on the rheology of the fluid as well as on the other parameters coming through imposed boundary conditions, inclusion of body force term and permeability of the porous medium. It is found that amplitude of flow velocity increases with increasing viscoelastic and mass suction/injection parameters. However, it decreases with increasing the strength of the applied magnetic field. Moreover, the temperature of fluid is a decreasing function of viscoelastic parameter, mass suction/injection parameter and Prandtl number.     

酶固定化的新型载体──PF凝胶应用研究

用对苯二酚和甲醛在酸催化下制得新一类凝胶,此凝胶价廉,易于制备,多孔、无毒、亲水性强;能选择性吸附多糖,而用于多糖与低聚糖及单糖的分离;可作为载体对多种酶及蛋白质给予固定,与蛋白质的最大结合量为558mg/g,固定糖化酶时的活力回收达84%;此固化酶对淀粉的转化率达93%,当加入一定量的间苯二酚,可得改性的PF凝胶,其性能又有提高,可见PF凝胶为新型的酶的固定化优良载体.     

Viscoelastic transition and yield strain of the folded protein

For proteins, the mechanical properties of the folded state are directly related to function, which generally entails conformational motion. Through sub-Angstrom resolution measurements of the AC mechanical susceptibility of a globular protein we describe a new fundamental materials property of the folded state. For increasing amplitude of the forcing, there is a reversible transition from elastic to viscoelastic response. At fixed frequency, the amplitude of the deformation is piecewise linear in the force, with different slopes in the elastic and viscoelastic regimes. Effectively, the protein softens beyond a yield point defined by this transition. We propose that ligand induced conformational changes generally operate in this viscoelastic regime, and that this is a universal property of the folded state.     

Porous silicon biosensor for detection of viruses

There is a growing need for virus sensors with improved sensitivity and dynamic range, for applications including disease diagnosis, pharmaceutical research, agriculture and homeland security. We report here a new method for improving the sensitivity for detection of the bacteriophage virus MS2 using thin films of nanoporous silicon. Porous silicon is an easily fabricated material that has extremely high surface area to volume ratio, making it an ideal platform for surface based sensors. We have developed and evaluated two different methods for covalent bioconjugation of antibodies inside of porous silicon films, and we show that the pore penetration and binding efficiency depend on the wettability of the porous surface. The resulting films were used to selectively capture dye-labeled MS2 viruses from solution, and a viral concentration as low as 2 x 10(7) plaque-forming units per mL (pfu/mL) was detectable by measuring the fluorescence from the exposed porous silicon film. The system exhibits sensitivity and dynamic range similar to the Luminex liquid array-based assay while outperforming protein micro-array methods.     

Optimal Homotopy Asymptotic Method for Flow and Heat Transfer of a Viscoelastic Fluid in an Axisymmetric Channel with a Porous Wall

In this article, an approximate analytical solution of flow and heat transfer for a viscoelastic fluid in an axisymmetric channel with porous wall is presented. The solution is obtained through the use of a powerful method known as Optimal Homotopy Asymptotic Method (OHAM). We obtained the approximate analytical solution for dimensionless velocity and temperature for various parameters. The influence and effect of different parameters on dimensionless velocity, temperature, friction factor, and rate of heat transfer are presented graphically. We also compared our solution with those obtained by other methods and it is found that OHAM solution is better than the other methods considered. This shows that OHAM is reliable for use to solve strongly nonlinear problems in heat transfer phenomena.     

Determining the effect of hydration upon the properties of ligaments using pseudo Gaussian stress stimuli

The level of tissue hydration is known to effect viscoelastic material properties. However, prior studies have not fully investigated the effect of hydration on dynamic behavior nor compared the results of transient and dynamic behavior. The material properties of medial collateral rat knee ligaments were studied in relation to hydration, using (sequentially) 0.3 osmolar artificial interstitial fluid (AIF), solutions of AIF plus sucrose with osmolarity 1.05, 1.80 or 2.55, and then AIF. In each solution, the complex compliance was determined as a function of frequency, and the creep response was measured. Complex compliance was determined from a constitutive model created by applying a 0.4+/-0.2 MPa pseudo Gaussian (PGN) stress stimulus to the ligament. Dehydration caused a reduction in cross-sectional area that was linearly related to the osmolarity of the solution. Reductions of up to 52% were observed and were reversible upon rehydration. Dehydration caused a reduction in the creep rate that was not immediately recovered upon rehydration. The storage compliance was reduced by up to 50% with dehydration; these changes were reversed upon rehydration. The loss compliance and phase angle were not affected by dehydration. Transient and dynamic experiments examine different viscoelastic characteristics and both types of tests appear to be necessary to fully characterize the effects of hydration.     

Viscoelastic properties and dynamics of porcine gastric mucin

Gastric mucin is a glycoprotein known to undergo a pH-dependent sol-gel transition that is crucial to the protective function of the gastric mucus layer in mammalian stomachs. We present microscope-based dynamic light scattering data on porcine gastric mucin at pH 6 (solution) and pH 2 (gel) with and without the presence of tracer particles. The data provide a measurement of the microscale viscosity and the shear elastic modulus as well as an estimate of the mesh size of the gel formed at pH 2. We observe that the microscale viscosity in the gel is about 100-fold lower than its macroscopic viscosity, suggesting that large pores open up in the gel reducing frictional effects. The data presented here help to characterize physiologically relevant viscoelastic properties of an important biological macromolecule and may also serve to shed light on diffusive motion of small particles in the complex heterogeneous environment of a polymer gel network.     

Test of a novel transparent floating carrier by recombinant cho cells expressing sIL6 receptor protein

We describe a carrier with some unusual properties.“Cellrafts” increase yields from adherent cells in conventional static T150 flasks, by floating multilayer strips of transparent film at the oxygen-rich surface of unstirred medium. This new technique allowed microscopic inspection of cell growth inside the carriers during bulk culture. Individual carriers could be picked out for subculture of selected colonies. A novel surface treatment by hypochlorite/uv allowed recycling of used carriers. Cellrafts' open-deck structure facilitated trypsinization with90% release as viable single cells from bulk carriers. Macro size (10mm by 1 mm) enables retention in flask by a coarse sieve insert in its neck, facilitating separation of product cells or media. Residual cells in carriers regenerated repeated harvests without need for reseeding. Carriers were tested with shear-sensitive CHO clones expressing soluble human IL6 receptor (sIL6R). Control was monolayer bulk culture on trays. Floating multilayer cultures remained viable longer than monolayers, had higher cellular activity of protein expression, and were less serum dependent (resembling cells on porous carriers). Purity and anti-sIL6R binding were identical to control product. Cellrafts were also tested in a small spinner vessel, but for litre batches this proved less convenient than in T-flasks. Though yields are low compared to well established porous carrier technology (spinner or packed bed) static transparent carriers might provide transitional scaleup from normal cytogenetics laboratory culture. This revised version was published online in August 2006 with corrections to the Cover Date.     

A computational model for dynamic analysis of the human gait

Biomechanical models are important tools in the study of human motion. This work proposes a computational model to analyse the dynamics of lower limb motion using a kinematic chain to represent the body segments and rotational joints linked by viscoelastic elements. The model uses anthropometric parameters, ground reaction forces and joint Cardan angles from subjects to analyse lower limb motion during the gait. The model allows evaluating these data in each body plane. Six healthy subjects walked on a treadmill to record the kinematic and kinetic data. In addition, anthropometric parameters were recorded to construct the model. The viscoelastic parameter values were fitted for the model joints (hip, knee and ankle). The proposed model demonstrated that manipulating the viscoelastic parameters between the body segments could fit the amplitudes and frequencies of motion. The data collected in this work have viscoelastic parameter values that follow a normal distribution, indicating that these values are directly related to the gait pattern. To validate the model, we used the values of the joint angles to perform a comparison between the model results and previously published data. The model results show a same pattern and range of values found in the literature for the human gait motion.     

Network structure of curdlan in DMSO and mixture of DMSO and water

The viscoelastic property of curdlan solution in dimethyl sulfoxide (DMSO) was investigated. We discuss the difference in the viscoelastic properties of curdlan solution in DMSO and that in 0.1 N NaOH aqueous solution. The viscoelastic function for curdlan solution in 0.1 N NaOH aqueous solution showed the Newtonian flow at the concentration of curdlan as high as 10 wt %. On the other hand, the Newtonian flow was observed in the concentrations below 7 wt % for curdlan solution in DMSO, and the plateau region appeared beyond this concentration. It was revealed by small angle x-ray diffraction measurements that the difference in the mechanical property would be originated from the difference in the network structure. The overlapping concentration c* was calculated on the basis of the mean field theory, and disagreement between theoretical prediction and experimental result was shown. We clarified that the above disagreement can be explained by the polydispersity of the curdlan sample, assuming adequate distribution functions. The static structure of the gel prepared by adding water to curdlan solution in DMSO was investigated. It was clarified by the dynamic viscoelasticity measurement that the cross-linking density increases with increasing the water content.