The effects of shear stress on isolated receptor-ligand interactions of Staphylococcus epidermidis and human plasma fibrinogen using molecularly patterned microfluidics

Staphylococcus epidermidis is an opportunistic pathogen that has been implicated in hospital-acquired infections, specifically related to implanted intravascular devices. S. epidermidis adhesion is a mechanism of colonization, leading to pathogenesis. Here we demonstrate an easily fabricated and robust parallel microfluidic platform to investigate the physiologically-relevant effects of fluid shear on S. epidermidis adhesion to human fibrinogen (hFg) with increased experimental throughput. In situ molecular patterning using fluid flow boundaries allows for isolation of the molecular interactions in highly defined shear stress environments, while keeping the device operation simple and reproducible. We characterize two modes of attachment of S. epidermidis to hFg coated surfaces. Single colonies adhere in high fractions at low shear stresses (~1 dyne cm(-2)) and adhesion decays with increasing shear. However, clusters of bacteria adhere the highest at median wall shear stress (up to 10 dyne cm(-2)), and adhesion subsequently decays above this critical shear stress. This initial characterization suggests a previously unobserved phenomenon of shear activated cell-cell adhesion in S. epidermidis, which acts to increase the overall attachment strength to hFg. Both of these modes of attachment are dependant upon the presence of intact hFg, indicating that adhesion is resultant from specific molecular recognition between the bacteria and human fibrinogen. This platform provides new insight into complex host-pathogen interactions, and will allow for further investigation of colonization and pathogenesis in more physiologically relevant conditions.     

Evaluating the performance of organic coatings under mechanical stress using electrochemical impedance spectroscopy

Stress in coatings originating from a mechanical load imposed during exploitation is a relatively unexplored field of investigation. Paradoxically, a number of constructions and installations seem to operate under such conditions. The purpose of this work was to investigate the impact of a cyclic mechanical load exerted on coating/metal systems. It was the authors aim to verify whether repeated mechanical stress constitutes a significant factor contributing to coating degradation. Epoxy coated St3SAl steel samples were subjected to 21,000 uniaxial strain/release cycles. The maximum force applied assured maintenance within the elastic deformation region of the metal substrate. The state of the protective film was monitored using electrochemical impedance spectroscopy. The coating response to the mechanical load occurred in a three-stage process. The system subjected to the strain/release cycles revealed signs of degradation earlier compared to a non-strained, reference sample.Contribution to the 3rd Baltic Conference on Electrochemistry GDASK-SOBIESZEWO, 23–26 April 2003.Dedicated to the memory of Harry B. Mark, Jr. (February 28, 1934–March 3rd, 2003)     

Evolution of nanometer voids in polycarbonate under mechanical stress and thermal expansion using positron spectroscopy

Positron Annihilation Lifetime Spectroscopy (PALS) measurements were conducted on polycarbonate subjected to either thermal expansion or to tensile and compressive strains. It was found that thermal expansion affected both the nanometer hole size and the hole number density, whereas mechanical stress affected mainly the size of existing holes, and did not generate or eliminate holes in the quasielastic deformation region. The effect of stress on yield and postyield behavior of this glassy material was also investigated. The deduced hole volume fraction of this polymer at 25°C was 6.8 ± 0.5% from the thermal expansion experiment and 7.2 ± 1.2% from the mechanical loading experiment. When the specimen was under compression, the hole volume fraction was found to continuously decrease. This can be considered as evidence of the inability of the free volume concept in explaining the yield behavior of glassy polymers. ©1995 John Wiley & Sons, Inc.     

Study on air pollution monitoring in Korea using low volume air sampler by instrumental neutron activation analysis

The aim of this research was to enhance the use of nuclear analytical techniques for air pollution studies and to study the feasibility of the use of instrumental neutron activation analysis (INAA) as a routine monitoring tool to reveal environmental pollution sources. For the collection of air particulate samples, the Gent stacked filter unit, low volume sampler with Nucleopore membrane filters were used. Trace elements in samples collected at two suburban residential sites, Taejon and Wonju city in the Republic of Korea, were analyzed by INAA. Variations of the elemental concentrations were measured monthly and the enrichment factors were calculated for the fine (<2 μm EAD) and coarse size (2–10 μm EAD) fractions. The analytical data were treated statistically to estimate the relationship between the two variables, the concentrations of elements and the total suspended particulate matter. The results were used to describe the emission source and their correlation.     

Optical,mechanical, and photoelastic anisotropy of biaxially stretched polyethylene terephthalate films studied using transmission ellipsometer equipped with strain camera and stress gauge

The anisotropic properties of polyethylene terephthalate film resulting from its manufacturing process are quantitatively investigated in terms of its optical, mechanical, and photoelastic aspects. Transmission ellipsometers and a Jones‐matrix‐based analysis software together with a 4 × 4 Berreman‐matrix‐based analysis software are adopted to determine the wavelength‐dependent in‐plane birefringence, the principal refractive indices, and the orientation of the optical axis. Mechanical anisotropy is characterized in terms of the elastic compliance tensor components using the measured azimuthal angle‐dependent Young's modulus and Poisson's ratio. From the measured variation of the wavelength‐dependent in‐plane birefringence as a function of tensile stress, the dispersive photoelastic coefficients are obtained for a few sample azimuthal angles, and the components of the photoelastic tensor are determined. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 152–160     

New powder coatings with low curing temperature and enhanced mechanical properties obtained from DGEBA epoxy resins and Meldrum acid using erbium triflate as curing agent

New low curing temperature powder coatings obtained by copolymerization of epoxy resins with Meldrum acid (MA) initiated by erbium (III) trifluoromethanesulfonate have been formulated. Their mechanical and thermomechanical properties have been studied and compared with a commonly used industrial system (o-tolylbiguanide/epoxy resin) and with an already formulated epoxy powder coating homopolymerized by erbium trifluoromethanesulfonate. Systems containing low proportions of MA and initiated by erbium trifluoromethanesulfonate lead to a great reduction of curing conditions (temperature/time). Moreover, the new formulated systems present very good mechanical properties, adhesion, and impact resistance. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2316–2327, 2007