Oscillational motion properties of bacteria and polystyrene particles on a positively polarized substrate surface.

The oscillational motion of bacteria and non-biological particles on a positively polarized substrate surface were investigated in this study using several bacterial species (Staphylococcus epidermidis ATCC12228 and Pseudomonas aeruginosa PA14) and polystyrene particles (modified with sulfate or carboxylate) that have different cell/particle size, surface potential, surface ionizable functional group, and surface appendage with respect to the mean square displacement (MSD) and motion trajectory. The attractive/repulsive interactions between the bacteria/particle and a positively polarized substrate surface are further discussed with the results of the motion analysis based on the extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. As our major findings, all the bacterial species and particles showed oscillational motion, a kind of sub-diffusive motion that is more limited than the Brownian motion of the suspended bacteria/particles, on a positively polarized substrate surface. However, the motion properties among the bacteria/particles were found to differ in motion radius and MSD. As the size and negative surface potential of the bacteria/particle got smaller, the oscillational motion became more active, which may result from a decrease in attractive interactions such as van der Waals interaction and electrostatic attractive interaction. In the case in which some surface functional group (e.g., sulfate group) contributed to the formation of a strong Lewis acid-base interaction, the oscillational motion was significantly reduced regardless of the surface potential of the particle. The bacterial surface appendages were found to have no influence in explaining motion differences between the bacteria and non-biological particle.

Bacterial translational motion on the electrode surface under anodic electric field.

Application of an electric field (alternating or cathodic polarization) has been suggested as a possible mean of controlling biofilm development. Bacteria on an anodically polarized surface were shown to be active and highly motile when compared with a nonpolarized condition, but no quantitative information on bacterial motion has been reported. This study investigated the effects of environmental conditions (current density and ionic strength) on the translational motion of P. aeruginosa PAO1 cells under an anodic electric field using a quantitative tracking method. Bacterial displacement for 10 s was found to be approximately 1.2 µm, irrespective of wide-ranging current densities (7.5-30 µA/cm(2)). However, the local dynamics of bacterial communities differed under varied current densities. The distribution of bacterial displacement appeared to exhibit a more oscillating (subdiffusive) at high current density. At the same time, the number of bacteria with a circular trajectory (superdiffusive) decreased. Bacterial movement decreased with increased ionic strength of the media, because of strong electrostatic interactions. The motion of bacterial communities on an anodically polarized surface under various conditions is discussed, along with possible mechanisms. In addition, the control of biofilm growth was partly demonstrated by changing the motility of bacterial cells under anodic polarization.

Extensional flow-based assessment of red blood cell deformability using hyperbolic converging microchannel.

The deformability of the red blood cell (RBC), is known to be closely related to microcirculation and diagnosis of specific diseases such as malaria, arterial sclerosis, sepsis, and so on. From the viewpoint of the flow type, conventional methods to measure the cell deformability have exploited simple shear or complex flow field with little focus on extensional flow field. In this paper, we present a new approach to assess cell deformability under the extensional flow field. For this purpose, a hyperbolic converging microchannel was designed, and the cell deformation in the extensional flow region was continuously monitored. It overcomes the limitation of conventional methods by reducing experiment time. As quantified by the degree of deformation, the extensional flow (Deformation Index = 0.51 at 3.0 Pa) was found to be more efficient in inducing cell deformation compared to the shear flow (Deformation Index = 0.29 at 3.0 Pa). This indicates the insufficiency of the existing models that predict the blood damage in artificial organs, which only consider shear flow. Also, this method could detect the heat-induced difference in deformability of RBCs. It provides a new platform to study the clinical effect of RBC deformability under extensional flow, and is expected to contribute the association of several diseases and deformability of RBCs.

Strain hardening of red blood cells by accumulated cyclic supraphysiological stress.

The effect of elevated shear stress upon cellular trauma has been studied for many years, but the effect of long-term cyclic stress trauma on hemorheology has never been explored systematically. This study investigated sublytic trauma of red blood cells (RBCs) caused by repeated exposure to shear stress. A suspension of bovine blood was throttled through a capillary tube (inner diameter 1 mm and length 70 mm) connected to a recirculating flow loop. Samples were withdrawn every 30 min to measure deformability and characteristic time. The deformability of the cell was measured microscopically by observing the shape of the cell during the shear flow. It was found that cyclic shear irreversibly stiffened the cell membrane while the effect was not so much as that of continuous shear. The cell deformability was dramatically reduced by 73% when the stress of 300 Pa was applied for 288 s, while it was 7% under 90 Pa. These results elucidate the need for improved models to predict cellular trauma within the unsteady flow environment of mechanical circulatory assist devices.