Shear Force Conditions Research Articles

Microbiology of human spaceflight: microbial responses to mechanical forces that impact health and habitat sustainability.

SUMMARYUnderstanding the dynamic adaptive plasticity of microorganisms has been advanced by studying their responses to extreme environments. Spaceflight research platforms provide a unique opportunity to study microbial characteristics in new extreme adaptational modes, including sustained exposure to reduced forces of gravity and associated low fluid shear force conditions. Under these conditions, unexpected microbial responses occur, including alterations in virulence, antibiotic and stress resistance, biofilm formation, metabolism, motility, and gene expression, which are not observed using conventional experimental approaches. Here, we review biological and physical mechanisms that regulate microbial responses to spaceflight and spaceflight analog environments from both the microbe and host-microbe perspective that are relevant to human health and habitat sustainability. We highlight instrumentation and technology used in spaceflight microbiology experiments, their limitations, and advances necessary to enable next-generation research. As spaceflight experiments are relatively rare, we discuss ground-based analogs that mimic aspects of microbial responses to reduced gravity in spaceflight, including those that reduce mechanical forces of fluid flow over cell surfaces which also simulate conditions encountered by microorganisms during their terrestrial lifecycles. As spaceflight mission durations increase with traditional astronauts and commercial space programs send civilian crews with underlying health conditions, microorganisms will continue to play increasingly critical roles in health and habitat sustainability, thus defining a new dimension of occupational health. The ability of microorganisms to adapt, survive, and evolve in the spaceflight environment is important for future human space endeavors and provides opportunities for innovative biological and technological advances to benefit life on Earth.

Ideal performance assessment of non-recirculating anaerobic fluidized bed reactors treating low to high strength organic loads with low retention time

This study investigated the ideal performance of non-recirculating Anaerobic Fluidized Bed Reactors (AnFBRs) for treating organic wastewater of varying strengths under low Hydraulic Retention Time (HRT). Four 4.58 L AnFBRs were used to treat synthetic wastewater with an Organic Loading Rate (OLR) ranging from 4.50 to 40.11 gCOD/L-d, and HRT between 1.1 and 4.4 hours. The AnFBRs achieved high removal efficiencies ranging from 83 % to 96 % at steady state, except during the organic shock load, which reduced removal performance to 12 %. Shortened HRT conditions led to a decreasing trend in reactor pH due to an incomplete anaerobic cycle. The modified Stover-Kincannon model estimated the maximum substrate utilization rate of AnFBR's to be 196.08 gCOD/L-d, with a correlation coefficient of 0.98. Under shortended HRT, microbial diversity analysis identified predominant non-filamentous bacterial families, such as Streptococcaceae and Veillonellaceae, which collaborate during biofilm development in anaerobic environments. It was suggested that the porous media provided secure attachment sites for the biomass growth and biofilm formation under shock load and high shear force conditions. While these results offer valuable insights, further studies are needed to confirm these findings and enhance the understanding of the use porous media in non-recirculating AnFBRs.

Wave motions due to a point source pulsating and advancing at forward speed parallel to a semi-infinite ice sheet

The Green function, or the wave motion due to a point source pulsating and advancing at constant forward speed along a semi-infinite ice sheet in finite water depth is investigated, based on the linear velocity potential theory for fluid flow and thin elastic plate model for the ice sheet. The result is highly relevant to the ship motions near marginal seas. The ice edge is assumed to be free, or zero bending moment and shear-force conditions are used, while other edge conditions can be similarly considered. The Green function G is derived first through the Fourier transform along the direction of forward speed and then by the Wiener-Hopf technique along the transverse direction across both the free surface and ice sheet. The result shows that in the ice-covered domain, G can be decomposed into three parts. The first one is that upper ocean surface is fully covered by an ice sheet, and the second and third ones are due to the free surface and ice edge. Similarly, in the free-surface domain, G contains the component corresponding to that the upper water surface is fully free, while the second and third ones are due to the ice sheet and ice edge. In both domains, the latter two are due to the interactions of the free-surface wave and ice sheet deflection, which leads to the major complication. In-depth investigations are made for each part of G, and aim to shed some light on the nature of the wave motions induced by a ship advancing along a semi-infinite ice sheet at constant forward speed. Published by the American Physical Society 2024

Experimental and numerical study on weld strengths of built-up steel box columns

This study investigates the demands generated in the panel zone of welded steel built-up box columns with fillet and complete joint penetration (CJP) groove welds, which are mainly used as columns in steel moment-resisting frames. The motivation for this study stems from the a 360–16 specification for structural steel building, which requires the joining of flange and web plates of box columns with CJP groove welds within a zone extending 12 in. above the upper beam flange and 12 in. below the lower beam flange in special and intermediate steel moment frames. Laboratory experiments have been conducted to examine the strength of these welds under pure shear forces. For this purpose, two laboratory specimens, one with fillet welds and the other with CJP groove welds, have been designed, and the strength of these welds were equal to each other in pure shear force conditions. The fillet weld specimen has resisted up to 1670 kN in the pure shear test, and the CJP groove weld has resisted up to 1520 kN. The entire loading process of each specimen was characterized by employing the digital image correlation (DIC) technique, which enabled the extraction of strain values throughout. Numerical modeling is validated in Abaqus software using experimental results, with comprehensive analyses on force-displacement diagrams and rupture. The outcomes of the tests conducted have shown that the demands generated in the panel zone of the built-up steel box welded sections are satisfactorily tolerated by both fillet and CJP groove welds. Research significanceThe significance of this study can be elaborated in multiple aspects. Firstly, it introduces an innovative test setup meticulously designed to replicate the behavior of welded built-up box columns with corner joints to steel plates. This advanced experimental arrangement not only facilitates the current study, but also serves as a versatile tool for conducting forthcoming experiments, allowing for meaningful comparisons and further exploration of diverse phenomena within the field. Secondly, the deliberate imposition of uniform demands on both types of welds during the study enables a comprehensive examination of their behavioral characteristics. This comprehensive analysis contributes to a more profound comprehension of welds performance under identical conditions, thereby enhancing our knowledge within the field. Finally, the research outcome, which reveals that fillet welds exhibit almost identical load-bearing capacity in comparison to CJP groove welds, bears substantial practical significance for the construction industry. This finding has the potential to instigate more cost-effective and efficient welding practices, which are paramount for maintaining the structural integrity of steel structures.In summary, this study makes a noteworthy contribution to the scientific community by presenting an innovative test setup, deepening the knowledge of weld performance, and suggesting practical enhancements in welding methodologies. These collective contributions serve to elevate the field of structural engineering, promoting advancements in construction practices.

Role of RpoS in Regulating Stationary Phase Salmonella Typhimurium Pathogenesis-Related Stress Responses under Physiological Low Fluid Shear Force Conditions.

The discovery that biomechanical forces regulate microbial virulence was established with the finding that physiological low fluid shear (LFS) forces altered gene expression, stress responses, and virulence of the enteric pathogen Salmonella enterica serovar Typhimurium during the log phase. These log phase LFS-induced phenotypes were independent of the master stress response regulator, RpoS (σS). Given the central importance of RpoS in regulating stationary-phase stress responses of S. Typhimurium cultured under conventional shake flask and static conditions, we examined its role in stationary-phase cultures grown under physiological LFS. We constructed an isogenic rpoS mutant derivative of wild-type S. Typhimurium and compared the ability of these strains to survive in vitro pathogenesis-related stresses that mimic those encountered in the infected host and environment. We also compared the ability of these strains to colonize (adhere, invade, and survive within) human intestinal epithelial cell cultures. Unexpectedly, LFS-induced resistance of stationary-phase S. Typhimurium cultures to acid and bile salts stresses did not rely on RpoS. Likewise, RpoS was dispensable for stationary-phase LFS cultures to adhere to and survive within intestinal epithelial cells. In contrast, the resistance of these cultures to challenges of oxidative and thermal stresses, and their invasion into intestinal epithelial cells was influenced by RpoS. These findings expand our mechanistic understanding of how physiological fluid shear forces modulate stationary-phase S. Typhimurium physiology in unexpected ways and provide clues into microbial mechanobiology and nuances of Salmonella responses to microenvironmental niches in the infected host. IMPORTANCE Bacterial pathogens respond dynamically to a variety of stresses in the infected host, including physical forces of fluid flow (fluid shear) across their surfaces. While pathogens experience wide fluctuations in fluid shear during infection, little is known about how these forces regulate microbial pathogenesis. This is especially important for stationary-phase bacterial growth, which is a critical period to understand microbial resistance, survival, and infection potential, and is regulated in many bacteria by the general stationary-phase stress response protein RpoS. Here, we showed that, unlike conventional culture conditions, several stationary-phase Salmonella pathogenic stress responses were not impacted by RpoS when bacteria were cultured under fluid shear conditions relevant to those encountered in the intestine of the infected host. These findings offer new insight into how physiological fluid shear forces encountered by Salmonella during infection might impact pathogenic responses in unexpected ways that are relevant to their disease-causing ability.

The effects of shear stress on the interaction between ADAMTS13 and VWF

<p indent="0mm">Both ADAMTS13 (a disintegrin and metalloprotease with a thrombosspondin type-1 motif, member 13) and VWF (von Willebrand factor) are critical in the regulation of platelet adhesion in hemostasis and thrombosis. Dysregulation of their functions is associated with thrombotic thrombocytopenic purpura (TTP) and von Willebrand disease (VWD). VWF is a multimeric glycoprotein discovered by Erik A. von Willebrand in 1926. It can bind and stabilize coagulation factor VIII. In addition, it can mediate platelet adhesion by binding to the components of the blood vessel wall and the glycoprotein Ib (GPIb) on the platelet membrane. Under physiology, VWF is synthesized as a disulfide-linked dimer in the endoplasmic reticulum and transported into the Golgi apparatus for further processing. In the Golgi, the intra- and inter-VWF disulfide bonds are reorganized so that VWF can polymerize into macro-molecular helices and be packed into Weibel-Palade Bodies in a tubular form. Upon stimulation by blood vessel injury, packed VWF can be rapidly unwound and released into the blood vessels, forming millimeter-long protein fibers. Under the stretch of increased shear force at the injury site, the cryptic platelet binding site on the A1 domain of VWF will be exposed, enabling the recruitment and aggregation of platelets on VWF fibers for hemostasis. However, the accumulation of ultra-long VWF in the blood would lead to the formation of microthrombi, blocking blood vessels and capillaries and causing the failure of multiple organs. To prevent thrombosis, multimeric VWF is cleaved by ADAMTS13 into short fragments to reduce platelet binding and aggregation. As such, the length and distribution of VWF multimers, which ADAMTS13 regulates, are essential for the precise balance between hemostasis and thrombosis. Unlike other proteases, which are secreted in an inactive state and activated proteolytically, ADAMTS13 is secreted in an active form and circulates in the blood as an active enzyme. Its activity is regulated by VWF binding and shear stress. Under resting state, the head and the tail of ADAMTS13 interact with each other to mask the exosites of ADAMTS13 on its DTCS domains. VWF binding induces conformational changes of ADAMTS13 to expose its exosites. On the other hand, shear stress not only causes the conformational changes of VWF to expose its ADAMTS13 cleavage site on the VWF A2 domain, but also regulates the interactions between VWF and ADAMTS13. Studies have shown that, under shear stress, VWF and ADAMTS13 need to be properly aligned so that the VWF A2 domain can be positioned in the vicinity of the ADATS13 M domain for cleavage. In this article, we summarize recent progress in the structural and functional studies of VWF and ADAMTS13. Primarily, we focus on how the conformations and interactions between VWF and ADAMTS13 are regulated under static and shear force conditions. The collected information will be helpful for better understanding the regulation of ADAMTS13 and VWF activities under physiological and pathological conditions. Such understanding could facilitate the screening and development of novel therapeutics in the treatment of TTP and VWD.

Hydrodynamic force on a ship floating on the water surface near a semi-infinite ice sheet

The hydrodynamic problem of wave interaction with a ship floating on the water surface near a semi-infinite ice sheet is considered based on the linearized velocity potential theory for fluid flow and the thin elastic plate model for ice sheet deflection. The properties of an ice sheet are assumed to be uniform, and zero bending moment and shear force conditions are enforced at the ice edge. The Green function is first derived, which satisfies both boundary conditions on the ice sheet and free surface, as well as all other conditions apart from that on the ship surface. Through the Green function, the differential equation for the velocity potential is converted into a boundary integral equation over the ship surface only. An extended surface, which is the waterplane of the ship, is introduced into the integral equation to remove the effect of irregular wave frequencies. The asymptotic formula of the Green function is derived and its behaviors are discussed, through which an approximate and efficient solution procedure for the coupled ship/wave/ice sheet interactions is developed. Extensive numerical results through the added mass, damping coefficient and wave exciting force are provided for an icebreaker of modern design. It is found that the approximate method can provide accurate results even when the ship is near the ice edge, through which some insight into the complex ship/ice sheet interaction is investigated. Extensive results are provided for the ship at different positions, for different ice sheet thicknesses and incident wave angles, and their physical implications are discussed.

Hierarchically porous piezoresistive sensor for application to the cambered palm of climbing robot with a high payload capacity

Effective sensitivity within a large responding range is a crucial parameter of flexible tactile sensors for a robot, especially for engineering climbing robots under high shear force conditions. While introducing microstructures can improve the sensitivity, in turn, it leads to a limited pressure-response range due to the poor structural compressibility. To achieve effective sensing under large loading forces, the flexible sensor needs to have a hierarchical sensing system and an optimal mechanic design. Herein, we report a strategy of embedded hierarchically porous piezoresistive foam that can significantly boost the sensitivity (S min > 0.084 kPa−1 at 20 Pa–500 kPa) while simultaneously broadening the pressure responding range, together with remarkable mechanical stability and robustness. Depending on the pressure distribution of the appreciable palm, the climbing robot with a high payload (40 kg) was demonstrated a series of recognitions of obstacles and feedback controls at slipping state. The soft piezoresistive material with the assembly architecture would be a general design expected to be applied to other types of robots to achieve a broader pressure-response range and a higher sensitivity.

Rheological and Impedance Measurements and Analysis of Catalyst Ink Prepared By Different Mixing Processes

Fundamental understanding of the state of catalyst inks such as agglomerate size and interparticle interaction is important to control mass transfer in the fabrication process and to fabricate well-established catalyst layers of proton exchange membrane fuel cells (PEMFCs). The catalyst ink is a slurry which contains platinum-supported carbon and ionomer in a solvent. The state of the catalyst ink affects the dynamics of materials during the fabrication process(1) and the porous structure of the catalyst layer as a result. The difficulty to evaluate the catalyst inks comes from their opacity and high particle concentration. Therefore, optical approaches are extremely limited. In addition, the time-dependency of the slurry should be considered. In this study, both rheological measurement and impedance measurement were conducted to characterize catalyst inks. The rheological measurement can apply to opaque and high concentration slurries like catalyst inks(2). The impedance measurement as well has a great potential to evaluate catalyst inks. The objective of this study is to establish evaluation methods of catalyst inks by rheological and impedance measurements especially focusing on the agglomerate size in the slurry.The rheological measurement was conducted by using a rheometer with a cone and plate system. Shear rate range was 300 to 3000 /s. The impedance measurement was conducted using an in-house electrochemical cell. The frequency range was 4 Hz to 8 MHz. The measurement temperature was 25°C. Carbon black (CB, Ketjenblack, Lion)–ionomer dispersion (pseudo-catalyst ink), and platinum-supported carbon (Pt/C, TEC10E50E, Tanaka Kikinzoku Kogyo)–ionomer dispersion (catalyst ink) were prepared. The volume fraction of carbon to the solvent (45wt.% 1-propanol aqueous solution) was approximately 2% and ionomer to carbon ratio (I/C) was 1.0. Two types of mixing tools were used. One was a centrifugal planetary mixer and the other was ultrasonic homogenizer. The slurries mixed only by the planetary mixer (one-step mixing) and mixed by the planetary mixer and the following ultrasonic homogenizer (two-step mixing) were measured.Figure 1(a) shows viscosity curves obtained from the rheological measurement. Two-step mixing showed lower viscosity in both CB slurry and Pt/C slurry. Pt/C slurries showed non-Newtonian behavior, whereas CB slurries showed Newtonian. Figure 1(b) shows the dielectric property of the slurries, which was obtained by impedance measurement. Two CB slurries showed a substantial difference in high frequency. The dielectric properties of the two Pt/C slurries were almost consistent with the one-step mixed CB slurry. Agglomerate size in the slurries was evaluated from the rheological measurements using the Krieger-Dougherty equation(3), and it was evaluated as well from the impedance measurement using the Schwarz equation(4). The rheological measurement showed smaller agglomerate size in the two-step mixed slurries, although the agglomerate size was several-hundred nanometer in both one-step and two-step mixed slurries. However, the impedance measurement showed several micrometers in the one-step mixed slurry. The impedance measurement can evaluate the slurries under a free state, whereas the rheological measurement evaluates the slurries under shear force conditions. Therefore, the impedance measurement could have detected a flocculated structure which is formed by a weak attractive force.AcknowledgmentsA part of this work was financially supported by JSPS KAKENHI Grant Number 18K13702 and 18H01383. This study was supported by Osaka University Nanofabrication Platform [S-19-OS-0011] in Nanotechnology Platform Project sponsored by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.References T. Suzuki, M. Kobayashi, H. Tanaka, M. Hayase, and S. Tsushima, ECS Trans., 69, 465 (2015).T. Suzuki, S. Okada, and S. Tsushima, ECS Trans., 86, 193 (2018).H. Chen, Y. Ding, and C. Tan, New Journal of Physics, 9, 367 (2007).G. Schwarz, The Journal of Physical Chemistry, 66, 2636 (1962). Figure 1

Characterization of four functional biocompatible pressure-sensitive adhesives for rapid prototyping of cell-based lab-on-a-chip and organ-on-a-chip systems

In the advent of affordable photo- and soft-lithography using polydimethylsiloxane (PDMS), low cost multi-step microfabrication methods have become available to a broad scientific community today. Although these methods are frequently applied for microfluidic prototype production in academic and industrial settings, fast design iterations and rapid prototyping within a few minutes with a high degree of flexibility are nearly impossible. To reduce microfluidic concept-to-chip time and costs, a number of alternative rapid prototyping techniques have recently been introduced including CNC micromachining, 3D printing and plotting out of numeric CAD designs as well as micro-structuring of thin PDMS sheets and pressure sensitive adhesives. Although micro-structuring of pressure sensitive adhesives promises high design flexibility, rapid fabrication and simple biochip assembly, most adhesives are toxic for living biological systems. Since an appropriate bio-interface and proper biology-material interaction is key for any cell chip and organ-on-a-chip system, only a limited number of medical-grade materials are available for microfluidic prototyping. In this study, we have characterized four functional biomedical-grade pressure sensitive adhesives for rapid prototyping (e.g. less than 1 hour) applications including structuring precision, physical and optical properties as well as biocompatibilities. While similar biocompatibility was found for all four adhesives, significant differences in cutting behavior, bonding strength to glass and polymers as well as gas permeability was observed. Practical applications included stability testing of multilayered, membrane-integrated organ-on-a-chip devices under standard cell culture conditions (e.g. 2–3 weeks at 37 °C and 100% humidity) and a shear-impact up to 5 dynes/cm2. Additionally, time- and shear-dependent uptake of non-toxic fluorescently labelled nanoparticles on human endothelial cells are demonstrated using micro-structured adhesive-bonded devices. Our results show that (a) both simple and complex microdevices can be designed, fabricated and tested in less than 1 hour, (b) these microdevices are stable for weeks even under physiological shear force conditions and (c) can be used to maintain cell monolayers as well as 3D cell culture systems.

Wave diffraction by a circular crack in an ice sheet floating on water of finite depth

The problem of wave diffraction by a circular crack in an ice sheet floating on water of finite depth is considered. The fluid flow is described by the linear velocity potential theory, while the infinitely extended ice sheet is modeled as a thin elastic plate with uniform properties. At the crack, zero bending moment and shear force conditions are enforced. The solution starts from the Green function for ice sheet without the crack. This is then used to obtain an integral equation, in which the jumps of the displacement and slope across the crack are the unknowns. For a circular crack, the unknowns are expanded into the Fourier series in the circumferential direction. Through imposing the boundary conditions at the crack, a matrix equation is obtained for the unknowns, which is then truncated and solved. Convergence study is undertaken with respect to the truncation, and it has been found that the series converges fast. A far field identity is used to verify the solution procedure and is found to be satisfied very accurately. Extensive results are provided, and their physical implications are discussed. These include the jumps of the displacement and slope across the crack, resonant motion, far field diffracted wave amplitude, and the deflection of the ice sheet.

Growth and aggregation control of spinel by shear-force-based melting modification of stainless steel slag

To improve the efficiency of melting modification for stainless steel (SS) slag, a shear force was introduced in this work and its effects on the spinel and silicate melt were experimentally investigated. The results indicated that the use of shear force changed the nucleation and growth behaviors of spinel and that the effects of shear force varied with its intensity. The aggregation behavior of spinel under different shear-force conditions was studied, revealing that large spinel clusters could be formed when the stirring speed was controlled. However, no notable change in the melt structure of the silicate was detected in this study. The optimal stirring speed for the melting modification treatment was 50 r·min−1, which substantially promoted spinel growth and aggregation, resulting in modified SS slag with excellent chromium sequestration capability.

Interaction of wave with a body submerged below an ice sheet with multiple arbitrarily spaced cracks

The problem of wave interaction with a body submerged below an ice sheet with multiple arbitrarily spaced cracks is considered, based on the linearized velocity potential theory together with the boundary element method. The ice sheet is modeled as a thin elastic plate with uniform properties, and zero bending moment and shear force conditions are enforced at the cracks. The Green function satisfying all the boundary conditions including those at cracks, apart from that on the body surface, is derived and is expressed in an explicit integral form. The boundary integral equation for the velocity potential is constructed with an unknown source distribution over the body surface only. The wave/crack interaction problem without the body is first solved directly without the need for source. The convergence and comparison studies are undertaken to show the accuracy and reliability of the solution procedure. Detailed numerical results through the hydrodynamic coefficients and wave exciting forces are provided for a body submerged below double cracks and an array of cracks. Some unique features are observed, and their mechanisms are analyzed.

On the interaction between a quartz crystal resonator and an array of micro-beams in thickness-shear vibrations

We studied the coupled dynamic behavior of a quartz-crystal-resonator (QCR)/microbeams system in the thickness-shear motions. Through taking into account the couple stress in the dynamic equations of the quartz plate, both continuous conditions of shear force and bending moment at the resonator/micro-beams interface are realized. Frequency shift of the compound QCR system induced by micro-beams is studied in detail. The obtained results are useful in device design and frequency-stability analysis of quartz crystal resonators.

Dynamic modulation of fimbrial extension and FimH-mannose binding force on live bacteria under pH changes: a molecular atomic force microscopy analysis.

Mechanical and conformational properties of type 1 fimbriae were evaluated on live bacterial cells by Single Molecule Force Spectroscopy (SMFS) and Dynamic Force Spectroscopy (DFS) in buffered solutions whose pH varied from 3 to 9. We evidenced that both fimbrial extension and fimbrial binding force to mannosylated-surface are modulated with changing the externally applied shear force and the solution pH. In particular, intertwined FimA-FimA and FimH-mannose interactions lead to a 5 to 25-fold decrease of the fimbrial unwinding for pulling rates larger than 10 μm/s and for pH values outside the range 5 to 7. In this pH range, the FimH-mannose binding force is maximal with a magnitude of -150-200 pN and the fimbriae extension reaches 8 μm. The enhancement of the FimH-mannose binding force at neutral pH, as evidenced from molecular AFM analyses, strongly correlates with an optimum in yeast agglutination detected at pH 5 to 7. The results reported in this work suggest that "catch bond effect" was negligible over the range of pulling rates tested, and both FimA-FimA and FimH-mannose interactions under given pH and external shear force conditions modify the ability of the bacteria to efficiently colonize host surfaces.

Free vibration analysis of thin isotropic and anisotropic rectangular plates by the discrete singular convolution algorithm

AbstractThis paper presents the free vibration analysis of thin isotropic and anisotropic rectangular plates with various boundary conditions by using the discrete singular convolution (DSC) algorithm. Based on Taylor's series expansion, a unique scheme is proposed to handle various boundary conditions, including the simply supported (S), clamped (C) and free (F) edge. To validate the proposed method, the non‐dimensional frequency parameters of isotropic, orthotropic and angle‐ply symmetric laminated rectangular plates with various combinations of boundary conditions are obtained by using the DSC algorithm and compared with the analytical and/or numerical solutions. Comparisons reveal that the proposed method can handle the zero bending moment and zero shear force conditions for the isotropic as well as anisotropic plates. The proposed method provides an alternative way for applying the simply supported boundary conditions in applications of the DSC algorithm to plate structures. This investigation extends the application range of the DSC algorithm to vibration analysis of anisotropic plates with various combinations of boundary conditions. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Development of a Disposable Microfluidic Biochip for Multiparameter Cell Population Measurements

An under recognized cause of preventable mortality is healthcare-associated (nosocomial) infections such as biofilms found on implants and catheters. About 5% of U.S. and E.U. patients acquire nosocomial infections leading to prolonged hospitalization, increased patient suffering, and mortality rates. To date, no satisfactory solutions are available to monitor biofilm formation under near-native conditions. As a consequence, in the present work, we report the development of a disposable microfluidic biochip capable of continuously monitoring cell population dynamics under physiological shear force conditions. We demonstrate the simultaneous application of contactless bioimpedance spectroscopy and amperometric measurements to monitor fungal biofilm growth rates and metabolic activities. Quantitative cell analysis is accomplished by the use of high-density interdigitated capacitors (microIDC) isolated by a 700 nm epoxy (SU-8 resist) based passivation layer to noninvasively assess biofilm formation in predefined proliferation chambers. Additionally, biofilm respiration activity is measured using redox-mediators oxidized at band electrodes located downstream within microchannels. The disposable biofilm analysis platform is used to continuously monitor the dynamic responses of C. albicans to different glucose and galactose concentrations.

SWNTs–polystyrene composites preparations and electrical properties research

Single-wall carbon nanotubes-filled polystyrene (SWNTs-PS) composites with 0–1.0% content have prepared successfully by a modified version of the suspension polymerization technique showed distinctive physical features, such as uniform black coloration and high solubility in toluene and tetrahydrofuran (THF). An adsorbed polymer layer on the nanotube bundles was found to contribute to a better dispersion of the inorganic nanoreinforcement. Stable suspension solution was formed by dispersing a hydrophobic monomer into water under high ultrasonic and adequate shear force conditions. DC resistivity and AC impedance measurements performed on the SWNTs–PS composites showed that the presence of SWNTs significantly modifies the electrical impedance of the composites. The obtained composites range from pure semiconductor to clear ohmic behavior as SWNTs loading increases in the composites.

Tissue macrophages: "satellite cells" for growing collateral vessels? A hypothesis.

It has been demonstrated in several studies that collateral growth is associated with accumulation of macrophages around proliferating vessel. Macrophages are known to secrete vascular growth factors and metalloproteinases. Both are necessary for the development of a proper vasculature. Recent studies suggest that certain subpopulations of macrophages are also capable of transdifferentiating into vascular cells. There are good reasons to assume that shear force rises dramatically in preexisting arteriolar shunts after occlusion of the main supplying vessel. Based upon these two findings it was hypothesized that high shear forces lead to homing of circulating monocytes to the growing collateral artery. The majority of studies, however, indicate that monocytes home under low shear force conditions. Our own observations in monocyte depleted animals suggest that proliferation and transdifferentiation of tissue macrophages occurs locally in growing collateral vessels and is independent of circulating cells. We thus propose that local proliferation and transdifferentiation of tissue macrophages rather than homing of circulating monocytes play a major role in arteriogenesis.

Investigation of the cellular uptake of E-Selectin-targeted immunoliposomes by activated human endothelial cells

In the present study the cellular uptake of targeted immunoliposomes by interleukin-1 activated human endothelial cells has been analysed by several spectroscopical and microscopical fluorescence techniques. Previous in vitro experiments demonstrated that the targeting of immunoliposomes to vascular selectins is a potential way for a selective drug delivery at inflammatory sites. In attempts to further adapt the targeting experiments to physiological conditions, we demonstrate that E-Selectin-directed immunoliposomes are able to bind their target cells under the simulated shear force conditions of capillary blood flow cumulatively for up to 18 h. In order to consequently follow the fate of liposomes after target binding, we analysed the route and degree of liposome internalization of the cells concentrating on cell activation state or various liposomal parameters, e.g., sterical stabilization, type of antibody or antibody coupling strategy. The use of NBD-labelled liposomes and subsequent fluorescence quenching outside the cells with dithionite show that circa 25% of the targeted immunoliposomes were internalized. According to inhibition experiments with agents that interfered with the endocytotic pathway, we found out that the major mechanism of liposome entry is endocytic. The entry involves, at least in part, receptor-mediated endocytosis via E-Selectin, a liposome accumulation in the endosomes and their acidification was proved by pyranine spectroscopic results. Furthermore, microscopical investigations demonstrate that also a fusion of liposomes with the cell membrane occurs followed by a release of entrapped calcein into the cytoplasm. These observations gain insight into the behaviour of E-Selectin-targeted immunoliposomes and indicate that these immunoliposomes have great potential to be used as drug carriers for intracellular drug delivery at inflammatory sites.