Generated Shear Stress Research Articles

Truncated flame structures within a deposit of the Indian Ocean Tsunami: evidence of syn‐sedimentary deformation

AbstractThis study reveals the three‐dimensional morphology and syn‐sedimentary formation processes of a deformation structure termed ‘truncated flame structures’ which is found in a terrestrial tsunami deposit in southern Thailand that formed during the 2004 Indian Ocean Tsunami. The structure was found at the boundary between a lower fine‐grained layer and an upper coarse‐grained layer that are related to two runup events. In order to confirm the morphology of the structure, the authors excavated two trenches and an opencast pit. When viewed in a cross‐section oriented parallel to the direction of the runup current, the deformed boundary has an irregularly bulging profile, similar to that observed in flame structures. The protruding structures are inclined towards the downstream direction of the runup current, and are truncated horizontally along their upper surface by parallel laminations in the overlying layer. When viewed in a cross‐section oriented perpendicular to the current direction, it appears that parts of the upper layer descend into the lower layer as lobate masses. In places, these masses are completely detached from the main part of the upper layer, forming circular or elliptical shapes. The contact between the lower layer and the main part of the upper layer is a planar truncation surface. Opencast excavation of the contact surface revealed that the deformed structures have flat, sinuous horseshoe crests that open in a downstream direction. It is possible for the runup current to generate shear stress such that it deforms the boundary into a truncated flame structure. Moreover, the observations made in this study indicate the syn‐sedimentary development of the structure: deformation and truncation occurred simultaneously in association with the runup current that formed the upper layer. Truncated flame structures can be used as a criterion in identifying the syn‐sedimentary deformation of substrate: the structures are indicative of unidirectional flow with sufficiently high shear velocity to deform unconsolidated substrate. As in the present case, the truncated flame structures may be characteristic of tsunami events that involve strong unidirectional currents on land due to the extraordinarily long wave period of tsunamis, rather than other events such as storm surges or flooding.

Vascular device interaction with the endothelium

Cerebral stents and Intra Aortic Balloon Pumps (IABP) are examples of mechanical devices that are inserted into arteries to restore flows to clinically healthy states. The stent and the IABP ‘correct’ the arterial flow by static dilation and by cyclical occlusion respectively. As this presentation shows, these functions are effectively modelled by current engineering practice. As interventions however, by their very nature they involve physical contact between a non-biological structure and the sensitive endothelial surface. The possible damage to the endothelium is not currently well addressed and we also consider this issue. Cerebral stents generally have two primary clinical objectives: to mechanically dilate a stenosed artery and to have minimal detrimental impact upon local blood flow characteristics. These objectives are well served at the arterial scale as these devices are evidently effective in opening up diseased arteries and restoring vital flows. However, at the near-wall micro-scale the picture is less satisfactory, as thin stent wires apply stresses to the endothelium and glycocalyx and the local flow is disturbed rather than being ideally streamlined. This causes further interaction with this endothelium topography. Wall Shear Stress (WSS) is the measure commonly used to indicate the interaction between fluid and wall but it is a broad brush approach that loses fidelity close to the wall. We will present simulation results of blood flow through a stented cerebral saccular aneurysm under these limitations of WSS. The Intra Aortic Balloon Pump (IABP) is a widely used temporary cardiac assist device. The balloon is usually inserted from the iliac artery, advanced in the aorta until it reaches the desired position; with its base just above the renal bifurcation and the tip approximately 10cm away from the aortic valve. The balloon is inflated and deflated every(1:1), every other(1:2) or every second (1:3) cardiac cycle. Balloon inflation, which takes place during early diastole, causes an increase in the pressure of the aortic root which leads to an increase in coronary flow. Balloon deflation which takes place during late diastole achieves one of the main IABP therapeutic effects by reducing left ventricular afterload. Unavoidably, the balloon contacts the inner wall of the aorta with every inflation/deflation cycle. This repeated event and possible contact with atherosclerotic plaque have been reported to be responsible for balloon rupture. However, there has not been a methodical study to investigate the mechanical effects of balloon-wall interaction. For example, during inflation the balloon approaches the endothelium as it displaces a volume of blood proximally and distally. This squeezing process generates shear stresses, which hasn’t yet been quantified. Similarly, when the balloon moves away from the endothelium during deflation, it generates micro pressure differences that may impose stretching (pulling) stresses on the endothelium cells. Both of the above cases indicate that a very high spatial resolution is required in order to fully understand the process of interaction between device and endothelium, and to interpret the effects at the cellular level.

Hygienic design: Effect of hydrodynamics on the cleanability of a food processing line

AbstractHydrodynamic effect on the numbers of adhering Bacillus cereus spores before and after cleaning in place of part of a dairy processing line was investigated using nonintrusive flow characterization (local wall shear stresses and velocity profiles measurements). Geometrical changes, like gradual asymmetric pipe contractions and pipe expansions and bends, induce nonhomogeneous distribution of the initial and the residual soiling levels. Moreover, the recirculation zone resulting from the flow detachment after the expansion, allowed to explain the high level of adhered spores downstream of this geometrical change due to the generated shear stresses. The resistance to cleaning processes in the same zones is mainly governed by the adhesion strength of spores induced by the applied flow rate in the contamination step. Welding and gasket areas, located at different positions in the loop, constituted deposit spots for spores and remained difficult to clean despite high‐shear stress forces involved. © 2008 American Institute of Chemical Engineers AIChE J, 2008

Comparison of PI‐SWERL with dust emission measurements from a straight‐line field wind tunnel

The Portable In situ Wind ERosion Lab (PI‐SWERL) was developed to measure dust emissions from soil surfaces. This small, portable unit can test the emissivity of soils in areas that are difficult to access with a field wind tunnel, and can complete a larger number of tests in less time. The PI‐SWERL consists of a cylindrical enclosure containing an annular flat blade that rotates at different speeds, which generates shear stress upon the surface. The shear stress generated by PI‐SWERL results in the entrainment of particles including dust. PI‐SWERL was developed to provide an index of dust emission potential comparable to the field wind tunnel. The PI‐SWERL dust emission results were compared against those obtained from a ∼12 m long, 1 m wide, 0.75 m high straight line suction‐type portable field wind tunnel by conducting collocated tests at 32 distinct field settings and soil conditions in the Mojave Desert of southern California. Clay‐ to sand‐rich soils that displayed a range of crusting, gravel cover, and disturbance were tested. The correspondence between dust emissions (mg m−2 s−1) for the two instruments is nearly 1:1 on most surfaces. Deviation between the two instruments was noted for densely packed gravel surfaces. For rough surfaces a correction can be applied to the PI‐SWERL that results in comparable dust emission data to the wind tunnel. PI‐SWERL can be used to complement research efforts in aeolian geomorphology aimed to quantify spatial and temporal patterns of dust emissions as well as air quality research related to dust emissions.

Neogene sedimentary deformation in the Chilean forearc and implications for Andean basin development, seismicity and uplift

Neogene sediments in the northern Chilean forearc display a wide range of near syndepositional structures. Analysis of the origin and distribution of these structures in space and time offers new insights into the development of the forearc basins. The structures are described in detail and show many features associated with soft-sediment deformation, pseudo-diapirism and slope failure. Synsedimentary deformation reached a peak in the Late Miocene to Early Pliocene while the sediments were saturated in a largely plastic state, and many of the structures were probably triggered by seismic shock. Late-stage tilting of the forearc generated shear stresses in the sediments leading to slumping and sliding. Base-level revision and drainage incision led to sediment bypass and cessation of lacustrine sedimentation that was not necessarily linked to climate change. Compaction and dewatering of the basins caused transition of the sediments from a plastic to a brittle state. The age and distribution of structures associated with seismicity appears to correlate with increasing subduction erosion and westward drift of South America but not with basin subsidence, shortening rates or plate convergence. This suggests that upper crustal deformation is at least partly decoupled from plate movement.

The Cumulative and Sublethal Effects of Turbulence on Erythrocytes in a Stirred-Tank Model

Mechanical forces generated by prosthetic heart devices (artificial valves, artificial hearts, ventricular assist devices) have been known to cause damage and destruction of erythrocytes. Turbulent flow within such devices generates shear stresses and can induce cell damage. Current models of cell damage rate utilize only the power input per unit mass as a modeling parameter. A stirred-tank reactor provides for a more extensive characterization of turbulence through eddy scale calculations. Through a simplified model, turbulence can be characterized by evaluating the Kolmogorov microscale. Our analysis of erythrocyte rupture in a stirred tank reactor suggests that parameters such as eddy wavelength and eddy velocity may better characterize and model the turbulent damage. Further, hemolysis of red blood cells by turbulent effects has been shown to have a fixed rate for constant levels of power input. Damage inflicted on the remaining, intact erythrocytes (sublethal damage) was evaluated by exposure to turbulence followed by osmotic fragility (OF) testing. Logistic models were fit to the OF data indicating a significant osmotic sensitivity in the sublethal damaged population between control and turbulence-exposed cells (chi(2) test; p < 0.001). This susceptibility indicates a significant cell population more susceptible to destruction as a result of turbulent exposure. This work has therefore helped identify optimization parameters for evaluating cell damage potential when engineering cardiovascular prosthetic devices.

NO‐mediated regulation of NAD(P)H oxidase by laminar shear stress in human endothelial cells

The flowing blood generates shear stress at the endothelial cell surface. In endothelial cells, NAD(P)H oxidase complexes have been identified as major sources of superoxide anion (.O(2)(-)) formation. In this study, we analysed the effect of laminar shear stress on .O(2)(-) formation by cytochrome c reduction assay and on NAD(P)H oxidase subunit expression by standard calibrated competitive reverse transcription-polymerase chain reaction and Western blot in human endothelial cells. Primary cultures of human umbilical vein endothelial cells were exposed to laminar shear stress in a cone-and-plate viscometer for up to 24 h. Short-term application of shear stress transiently induced .O(2)(-) formation. This was inhibited by NAD(P)H oxidase inhibitor gp91ds-tat, but NAD(P)H oxidase subunit expression was unchanged. Long-term arterial laminar shear stress (30 dyne cm(-2), 24 h) down-regulated .O(2)(-) formation, and mRNA and protein expression of NAD(P)H oxidase subunits Nox2/gp91(phox) and p47(phox). In parallel, endothelial NO formation and eNOS, but not Cu/Zn SOD, protein expression was increased. Down-regulation of .O(2)(-) formation, gp91(phox) and p47(phox) expression by long-term laminar shear stress was blocked by l-NAME. NO donor DETA-NO down-regulates .O(2)(-) formation, gp91(phox) and p47(phox) expression in static cultures. In conclusion, our data suggest a transient activation of .O(2)(-) formation by short-term shear stress, followed by a down-regulation of endothelial NAD(P)H oxidase in response to long-term laminar shear stress. NO-mediated down-regulation by shear stress preferentially affects the gp91(phox)/p47(phox)-containing NAD(P)H oxidase complex. This mechanism might contribute to the regulation of endothelial NO/.O(2)(-) balance and the vasoprotective potential of physiological levels of laminar shear stress.

Shear Stress Effect on the Absorption Spectra of Organic Thin Films Under High Pressure

The effects of shear stress on the absorption spectra of a thin film of one-dimensional bis(diphenylglyoximato)platinum(II), Pt(dpg)2 have been studied under high pressure. The color of the thin film turns from red-brown at ambient pressure to green at 0.4 GPa. Then, one sapphire anvil is rotated by applied force in order to generate shear stress at 0.4 GPa. The color of the thin film at the outer part on the anvil changes remarkably from green to yellow, but the color at the center is green. The absorption spectra of Pt(dpg)2 have simultaneously been measured under shear deformation and non-hydrostatic conditions. The absorption intensity of the visible band decreases sharply at outer part, and this absorption peak abruptly shifts to the near-infrared region. The powder x-ray diffraction profiles of the thin film of Pt(dpg)2 at center and outer parts have been studied under shear deformation. The 110 and 200 lines at outer part markedly shift to the lower d-value region. In contrast, both diffraction lines at the center part are insensitive to shear stress. This behavior corresponds to the shift of the absorption band at outer part.

Effects of Pressure and Shear Stress on the Absorption Spectra of Thin Films of Pentacene

The absorption spectra in an oriented film of pentacene have been studied up to 10 GPa under hydrostatic conditions. The absorption bands of this hydrocarbon rapidly shifted to a longer wavelength region. The Davydov splitting of the 0-0 band in the oriented film abruptly increased with increasing pressure up to 1.2 GPa. However, this splitting disappeared at around 1.5 GPa. The absorption spectrum at this pressure is similar to that of the amorphous film. The molecular arrangements in the oriented film of pentacene changed to the amorphous state at around 1.5 GPa. When the pressure was increased further, the absorption peaks disappeared at pressures greater than 6.6 GPa. When the pressure is reduced from 10 GPa to the ambient pressures, we cannot find the original absorption spectra of the oriented film of pentacene. The irreversible optical property arises from the solid-phase reaction at higher pressures. We have observed in situ shear stress effects on the oriented film of pentacene in the sapphire-anvil cell under the microscope. After the pressure is increased up to 2 GPa, one sapphire-anvil is rotated by applied force to generate shear stress at this pressure. The color of the thin film changed remarkably from blue to yellow at the outer part on the anvil, but the color at the center was blue, insensitive to shear stress. The absorption intensity of the visible bands sharply decreased, and the width vastly broadened in the outer part. The amorphization of the oriented film is accelerated under shear deformation. On the other hand, the intensity of the absorption band below 400 nm increased in the outer part. After shear stress was reduced, the original spectrum of pentacene did not recover completely. The conjugated system in pentacene is partly broken by shear stress. Thus, the solid-phase reaction is also induced by shear stress for the thin film.

Numerical simulations of frictional melting: Small dependence of shear stress drop on viscosity parameters

Frictional melting during coseismic slipping strongly affects dynamic sliding. An idealized numerical simulation of shear stress drop due to lubrication of fault surfaces by frictional melting is performed to investigate dynamical adjustment of melt thickness and its dependence on material properties. We numerically solved one‐dimensional heat conduction equations coupled with hydrodynamic equations of motion of the melt layer. We adopt a simple Arrhenius‐type temperature dependence of melt viscosity with a parametric factor η0. After the initial transient stage, the evolution of the melt layer asymptotes to the late stage, where the melt thickness increases as and the generated shear stress drops as 1/. An analytic self‐similar solution of the temperature profile for the late stage is obtained. The balance between the viscous heat generation and conductive heat loss characterizes the late stage. For small η0, the melt thickness is proportional to η0, whereas it will saturate for a larger η0. This is because the strong temperature dependence of viscosity enables an automatic adjustment of viscosity, which drops through the temperature increase due to the viscous heating even if a large η0 is chosen. Numerical results and the thickness data of natural pseudotachylyte layers were compared. A maximum ratio X/ (X is thickness, D is sliding distance) exists above which no solution is found. The effective thermal conductivity of the melt layer should be large, probably due to the sliding surface roughness. Comparison with laboratory experimental results showed that the normal stress applied to the sample is an important parameter for stress drop.

Optical studies of shear stress effect on organic thin films

We have studied the effect of shear stress by using the sapphire-anvil cell, which was developed to generate shear stress on a thin film under high pressure. We have tried to synthesize the charge-transfer (CT) salt of TMPD ( N, N, N′, N′-tetramethyl-p-phenylenediamine) and TCNQ (7,7,8,8,-tetracyanoquinodimethane) by the shear stress effect. The shear deformation caused a change of the color of the thin film to blue-black at the outer part on the sapphire culet, while the color at the center part remained as orange of neutral TCNQ. The thin film on the anvils was examined by Raman spectroscopy under a microscope. The Raman bands attributed to C C of TCNQ were observed at 1386 cm −1 and 1452 cm −1 for the CT salt and neutral TCNQ, respectively. For the blue-black thin film at the outer part, the Raman band appeared at 1386 cm −1, while at the center part, it was observed at 1452 cm −1. From the Raman spectra, the formation of the CT salt from TMPD and TCNQ by the shear stress effect was confirmed. In addition, the estimation of the shear stress effect on Pt(dpg) 2, bis(diphenylglyoximato)-platinum(II), was performed by comparing the Raman band under the shear stress with one under hydrostatic pressure. It was noted that the shear stress with the sapphire anvil cell was applied more strongly at the outer part on the culet than at the center part.

Keratin 8 Phosphorylation by Protein Kinase C δ Regulates Shear Stress-mediated Disassembly of Keratin Intermediate Filaments in Alveolar Epithelial Cells

Phosphorylation of keratin intermediate filaments (IF) is known to affect their assembly state and organization; however, little is known about the mechanisms regulating keratin phosphorylation. In this study, we demonstrate that shear stress, but not stretch, causes disassembly of keratin IF in lung alveolar epithelial cells (AEC) and that this disassembly is regulated by protein kinase C delta-mediated phosphorylation of keratin 8 (K8) Ser-73. Specifically, in AEC subjected to shear stress, keratin IF are disassembled, as reflected by their increased solubility. In contrast, AEC subjected to stretch showed no changes in the state of assembly of IF. Pretreatment with the protein kinase C (PKC) inhibitor, bisindolymaleimide, prevents the increase in solubility of either K8 or its assembly partner K18 in shear-stressed AEC. Phosphoserine-specific antibodies demonstrate that K8 Ser-73 is phosphorylated in a time-dependent manner in shear-stressed AEC. Furthermore, we showed that shear stress activates PKC delta and that the PKC delta peptide antagonist, delta V1-1, significantly attenuates the shear stress-induced increase in keratin phosphorylation and solubility. These data suggested that shear stress mediates the phosphorylation of serine residues in K8, leading to the disassembly of IF in alveolar epithelial cells. Importantly, these data provided clues regarding a molecular link between mechanically induced signal transduction and alterations in cytoskeletal IF.

Osteocyte lacunae tissue strain in cortical bone

Current theories suggest that bone modeling and remodeling are controlled at the cellular level through signals mediated by osteocytes. However, the specific signals to which bone cells respond are still unknown. Two primary theories are: (1) osteocytes are stimulated via the mechanical deformation of the perilacunar bone matrix and (2) osteocytes are stimulated via fluid flow generated shear stresses acting on osteocyte cell processes within canaliculi. Recently, much focus has been placed on fluid flow theories since in vitro experiments have shown that bone cells are more responsive to analytically estimated levels of fluid shear stress than to direct mechanical stretching using macroscopic strain levels measured on bone in vivo. However, due to the complex microstructural organization of bone, local perilacunar bone tissue strains potentially acting on osteocytes cannot be reliably estimated from macroscopic bone strain measurements. Thus, the objective of this study was to quantify local perilacunar bone matrix strains due to macroscopically applied bone strains similar in magnitude to those that occur in vivo. Using a digital image correlation strain measurement technique, experimentally measured bone matrix strains around osteocyte lacunae resulting from macroscopic strains of approximately 2000 microstrain are significantly greater than macroscopic strain on average and can reach peak levels of over 30,000 microstrain locally. Average strain concentration factors ranged from 1.1 to 3.8, which is consistent with analytical and numerical estimates. This information should lead to a better understanding of how bone cells are affected by whole bone functional loading.

Photocatalytic Inactivation of Legionella Pneumophila and an Aerobic Bacteria Consortium in Water over TiO2/SiO2 Fibres in a Continuous Reactor

A continuous photoreactor, working in a total recycle mode and irradiated by a low-pressure Hg lamp, has been used to study the bactericidal effect of a photocatalyst, formed by TiO2 embedded in SiO2 fibres, on Legionella pneumophila and a consortium of common gram-negative aerobic bacteria (Escherichia coli, Klebsiella sp., Pseudomona sp. and Proteus sp.) in water. The kinetic modeling of the inactivation process, carried out with the measured values of viable bacteria concentration at the outlet of photoreactor, evidenced that for each pass inside the photoreactor the ratio between the outlet and inlet cell concentrations was of order of 0.01 for the inactivation of L. pneumophila. For the other aerobic bacteria, which are usually taken as reference in photocatalytic bacteria inactivation studies, this ratio was of order of 0.3 for the first hour of illumination, while upon prolonged irradiation (up to 9 h) this ratio increased to 0.7. Several factors inducing this latter decrease of efficiency are possible, as e.g. competition for photocatalytic attack between microorganisms and organic compounds released by damaged bacteria or photoinduced alteration of a small fraction of still viable bacteria making them less interactive with the photocatalyst. The inactivation mechanism normally proposed for common bacteria involves an initial attack of the photogenerated radicals to the outer membrane; the consequent membrane dispersion allows the radicals to damage the cytoplasmic membrane. The higher lethality of the photocatalytic method observed towards Legionella (in comparison to the other aerobic bacteria) is explained considering that the radicals attack the Legionella secretion system, which is adapted for high virulence and would become activated for and through adhesion to the TiO2 surface. This attack would then be able to inactivate L. pneumophila without dispersing the outer membrane. Apart from this, the water flow through the catalyst fibres can facilitate the bacteria transport towards the anatase surface, and additionally the generated shear stress may help adhesion, at least for some bacteria as E. coli, contributing further to improve the photokilling efficiency; both factors may contribute to the efficiency of this photoreactor configuration.

Design Optimization of Blood Shearing Instrument by Computational Fluid Dynamics

Rational design of blood-wetted devices requires a careful consideration of shear-induced trauma and activation of blood elements. Critical levels of shear exposure may be established in vitro through the use of devices specifically designed to prescribe both the magnitude and duration of shear exposure. However, it is exceptionally difficult to create a homogeneous shear-exposure history by conventional means. This study was undertaken to develop a Blood Shearing Instrument (BSI) with an optimized flow path which localized shear exposure within a rotating outer ring and a stationary conical spindle. By adjustment of the rotational speed and the gap dimension, the BSI is designed to generate shear stress magnitudes up to 1500 Pa for exposure time between 0.0015 and 0.20 s with a pressure drop of 100 mm Hg. Computational fluid dynamics (CFD) revealed that a flow path designed by first-order analysis and intuition exhibited unfavorable pressure gradient, vortices, and undesirable regions of reverse flow. An optimized design was evolved utilizing a parameterized geometric model and automatic mesh generation to eliminate vortices and reversal flow and to avoid unfavorable pressure gradients. Analysis of the flow and shear fields for the extreme limits of the shear gap demonstrated an improvement in homogeneity due to shape optimization and the limitations of an annular shear device for achieving completely uniform shear exposure.

Phospholipid polymer surfaces reduce bacteria and leukocyte adhesion under dynamic flow conditions

Persistence of infection can occur when the host immune response is compromised because of the presence of a foreign implant. Surface modification of biomaterials with phospholipid polymers may enhance biocompatibility and reduce incidence of infection by impeding bacterial and leukocyte adhesion. A rotating disk model, which generates shear stress from 0 to 18 dynes/cm(2), was used to characterize adhesion of neutrophils, monocytes, and bacteria in phosphate-buffered saline (PBS) or 25% human serum on polyethylene terephthalate surfaces coated with a phospholipid polymer, poly[omega-methacryloyloxyalkyl phosphorylcholine (MAPC)-co-n-butyl methacrylate (BMA)]. The material designated PMB30 contains a methylene chain length, (CH(2))(n), of n = 2, whereas PMHB30 contains a chain length of n = 6. In PBS, bacterial adhesion was shear stress dependent with the lowest bacterial density observed on PMB30. However, the presence of serum proteins eliminated shear stress and surface chemistry effects in addition to bacterial adhesion reduced to <10% of adhesion in PBS. Trends for leukocyte adhesion in serum demonstrated shear dependence with PMB30 exhibiting the lowest cell density throughout the range of shear stresses. In conclusion, modification of the polyethylene terephthalate surfaces with phospholipid polymers resulted in reduced bacterial and leukocyte adhesion. Furthermore, shortening the methylene chain length of the MAPC copolymer most effectively reduced adhesion.

Electrorheological Response of Silicone Oil Suspension of Barium Strontium Titanate Particles with Different Surface Compositions

Electrorheological response of barium strontium titanate (BST)/silicone oil suspension was experimentally studied with measurements of generated shear stress in a range of field frequency (200-4000 Hz) under steady shear. The BST particles were synthesized by the hydrolysis of complex alkoxide precursor that was prepared in a reflux of metallic barium, metallic and tetraethylorthotitanate in solvent. The hydrolysis was performed by the addition of water/ethanol solution to the precursor solution. Generated shear stress of as-prepared (unannealed) BST particles system decreased with an increase in frequency, while that for 1100 °C-annealed BST system increased with frequency. XPS measurements revealed that alkoxyl groups that were derived from unreacted alkoxide were on surface of the as-prepared BST particles, and the annealing at 1100 °C decomposed the alkoxyl groups to hydroxyl groups. Difference in electric conductivities of the surfaces is considered to be responsible for the different shear stress behaviors of the as-prepared and annealed particles.

Inhibition of bacterial and leukocyte adhesion under shear stress conditions by material surface chemistry

Biomaterial-centered infections, initiated by bacterial adhesion, persist due to a compromised host immune response. Altering implant materials with surface modifying endgroups (SMEs) may enhance their biocompatibility by reducing bacterial and inflammatory cell adhesion. A rotating disc model, which generates shear stress within physiological ranges, was used to characterize adhesion of leukocytes and Staphylococcus epidermidis on polycarbonate-urethanes and polyetherurethanes modified with SMEs (polyethylene oxide, fluorocarbon and dimethylsiloxane) under dynamic flow conditions. Bacterial adhesion in the absence of serum was found to be mediated by shear stress and surface chemistry, with reduced adhesion exhibited on materials modified with polydimethylsiloxane and polyethylene oxide SMEs. In contrast, bacterial adhesion was enhanced on materials modified with fluorocarbon SMEs. In the presence of serum, bacterial adhesion was primarily neither material nor shear dependent. However, bacterial adhesion in serum was significantly reduced to 10% compared to adhesion in serum-free media. Leukocyte adhesion in serum exhibited a shear dependency with increased adhesion occurring in regions exposed to lower shear-stress levels of 7 dyne/cm2. Additionally, polydimethylsiloxane and polyethylene oxide SMEs reduced leukocyte adhesion on polyether-urethanes. In conclusion, these results suggest that surface chemistry and shear stress can mediate bacterial and cellular adhesion. Furthermore, materials modified with polyethylene oxide SMEs are capable of inhibiting bacterial adhesion, consequently minimizing the probability of biomaterial-centered infections.

Shear stress effects on electronic spectra on the one-dimensional bis(diphenylglyoximato)metal (II) complexes, M(dpg)2 [M=Ni and Pt] under high pressure

We have developed a new sapphire-anvil cell to generate shear stress at high pressures. The new cell is similar to a diamond-anvil cell. Bis(diphenylglyoximato)metal(II), M(dpg)2(M = Ni and Pt) are pressure-sensitive one-dimensional metal complexes. By use of this cell we have observed in situ the shear stress effect on a thin film of M(dpg)2 under the microscope. Furthermore, electronic absorption spectra of both complexes have been simultaneously measured under applied shear deformation and non-hydrostatic conditions. When the pressure is increased, the color of a thin film of Pt(dpg)2 turns from red-brown at ambient pressure to green at 0.4 GPa. One sapphire anvil is rotated by applied force in order to generate the shear stress at 0.4 GPa. The color of the thin film changes remarkably from green to yellow at the outer part on the anvil, but the color at the center is green, insensitive to the shear stress. The region changed by the shear stress can be observed with the naked eye. Absorption spectra of the yellow region at the outer part change markedly; the intensity of the d-p band decreases sharply and this peak abruptly shifts to the near-infrared region. On the other hand, electronic spectra at the center part are insensitive to the shear deformation. The similar shear stress effect on the optical spectrum of Ni(dpg)2 is also observed. We have found that electronic states of M(dpg)2 essentially change by applying shear deformation.(Contributed by Hiroo INOKUCHI, M. J. A., Nov. 12, 2003)

Interaction of transmural pressure and shear stress in the transport of albumin across the rabbit aortic wall

In this study the synergistic role of the two haemodynamic parameters, pressure and wall shear stress, in macromolecular transport has been examined across the wall of the rabbit thoracic aorta. Arteries were subjected to 70 and 150 cm water pressure in the presence of fluid flow imposed shear stress. The flux of FITC labelled bovine serum albumin was found to be 3.36±1.34×10 −6 and 1.99±0.77×10 −6 cm/s (mean±S.D.) after 90 min incubation at 70 and 150 cm water, respectively. The mean relative tissue concentrations were 0.0039±0.0025 and 0.012±0.007 at 70 and 150 cm water, respectively. Under low values of steady wall shear stress, efflux of BSA is retarded at 150 cm since its tissue concentration is found to be higher than at 70 cm. The net outcome arises as a result of the interaction of increased permeability of endothelial cells exposed to shear stress, the pressure induced distension of the wall matrix and the differential effect of EDRF/NO at the two pressures on medial hydraulic conductivity. In the presence of the EDRF/NO inhibitor l-NAME, reduction in flux of albumin was observed at both the pressures, the decrease being greater at 150 cm water. In the absence of EDRF, the NO synthase independent vasodilator EDHF may be released, which maintains the tone of the medial smooth muscle low. Action of EDHF may be more marked at 150 cm water because NO synthesis is attenuated by higher transmural pressure and the presence of l-NAME eliminates shear stress stimulated NO release. Consequently the dilated vessel will have decreased porosity and less albumin space. The BSA flux across the aorta is, therefore, influenced by both endothelial permeability and permeability of the medial matrix, which are in turn modulated by an interplay of transmural pressure and fluid flow generated shear stress.