(RBCs) generally deform to adopt a parachute-like, torpedo-like, or other configuration to align and flow through a capillary that is narrower than their major axis. As described herein, even in a narrow tube (25 m) with diameter much larger than that of a capillary, flowing RBCs at 1 mm/s align axially and deform to a paraboloid shape in a viscous Newtonian fluid (505 kDa dextran medium) with viscosity of 23.4 -57.1 mPa ⅐ s. A high-speed digital camera image showed that the silhouette of the tip of RBCs fits a parabola, unlike the shape of RBCs in capillaries, because of the longer distance of the RBC-free layer between the tube wall and the RBC surface (ϳ8.8 m). However, when RBCs are suspended in a "non-Newtonian" viscous fluid (liposome-40 kDa dextran medium) with a shear-thinning profile, they migrate toward the tube wall to avoid the axial lining, as "near-wall-excess," which is usually observed for platelets. This migration results from the presence of flocculated liposomes at the tube center. In contrast, such near-wall excess was not observed when RBCs were suspended in a nearly Newtonian liposome-albumin medium. Such unusual flow patterns of RBCs would be explainable by the principle; a larger particle tends to flow near the centerline, and a small one tends to go to the wall to flow with least resistance. However, we visualized for the first time the complete axial aligning and near-wall excess of RBCs in the noncapillary size tube in some extreme conditions. hemorheology; erythrocytes; viscometry; artificial red cells; microcirculation RED BLOOD CELLS (RBCs) or erythrocytes in mammals lost their nuclei during their evolution and specialization for their role of oxygen transport. Microcirculatory observation of capillaries (Ͼ4 m diameter) that are narrower than the RBC diameter (8 m) revealed that flowing RBCs alter their own morphology from a biconcave disk to various configurations resembling a parachute, umbrella, jellyfish, or torpedo, as though they were alive (10,11,29). This phenomenon was first reported in the 1960s.During blood flow in a capillary, a pressure gradient exists: a pressure drop in the direction of flow. The higher pressure in the rear tends to compress the rear portion of the RBCs. In response to such stress, the elastic cellular structure of RBCs (biconcave disc) is known to be effective to deform and stir the intracellular viscous hemoglobin (Hb) solution (Ͼ35 g/dl), thereby facilitating gas exchange (1,6,14). From conventional microscopic observation of peripheral tissues, it is difficult to discern the capillary shape, especially at a reduced hematocrit resulting from the Fahraeus effect and plasma skimming, but we can infer the presence of functional capillary walls near the RBCs by the presence of deformed and aligned RBC flow (25,29). In glass tubes (inner diameter, Ͻ12 m), similar deformation of RBCs is apparent (8, 35). On the other hand, the glycocalyx layer of the capillary endothelium interacts with the plasma layer fluid and retards its flow. Its hydraulic resista...

Sakai H, Okuda N, Sato A, Yamaue T, Takeoka S, Tsuchida E. Hemoglobin encapsulation in vesicles retards NO and CO binding and O2 release when perfused through narrow gas-permeable tubes. Am J Physiol Heart Circ Physiol 298: H956 -H965, 2010. First published December 31, 2009 doi:10.1152/ajpheart.00741.2009.-Intravenous administration of cell-free Hb induces vasoconstriction and circulatory disorders, presumably because of the intrinsic affinities to endogenous nitric oxide (NO) and carbon monoxide (CO) as vasorelaxation factors and because of the facilitated O2 release that might induce autoregulatory vasoconstriction. We examined these gas reactions when Hb-containing solutions of four kinds were perfused through artificial narrow tubes at a practical Hb concentration (10 g/dl). Purified Hb solution, polymerized bovine Hb (Poly BHb), encapsulated Hb [Hb-vesicles (HbV), 279 nm], and red blood cells (RBCs) were perfused through a gas-permeable narrow tube (25 m inner diameter) at 1 mm/s centerline velocity. The level of reactions was determined microscopically based on the visible-light absorption spectrum of Hb. When the tube was immersed in NO and CO atmospheres, both NO binding and CO binding of deoxygenated Hb (deoxy-Hb) and PolyBHb in the tube was faster than those of HbV and RBCs, and HbV and RBCs showed almost identical binding rates. When the tube was immersed in a N2 atmosphere, oxygenated Hb and PolyBHb showed much faster O 2 release than did HbV and RBCs. PolyBHb showed a faster reaction than Hb because of the lower O2 affinity of PolyBHb than Hb. The diffusion process of the particles was simulated using Navier-Stokes and Maxwell-Stefan equations. Results clarified that small Hb (6 nm) diffuses laterally and mixes rapidly. However, the large-dimension HbV shows no such rapid diffusion. The purely physicochemical differences in diffusivity of the particles and the resulting reactivity with gas molecules are one factor inducing biological vasoconstriction of Hb-based oxygen carriers. microcirculation; blood substitutes; gas biology; liposome; erythrocytes CELL-FREE, HEMOGLOBIN-BASED oxygen carriers (HBOCs) have been developed for use as transfusion alternatives. Some examples are intramolecular cross-linked Hb, polymerized Hb, and polyethylene glycol conjugated Hbs (5). The realization of HBOCs has long been anticipated, because they are free of pathogens and blood-type antigens and are storable for a long time for using at emergency situations. Some are in the final stage of clinical trials (23). The major remaining hurdle before clinical approval of this earliest generation of HBOCs is vasoconstriction and resulting hypertension, which are presumably attributable to the high reactivity of Hb with endothelium-derived nitric oxide (NO) (26,28,55). It has been suggested that small molecular Hbs permeate across the endothelial cell layer to the space near by the smooth muscle and inactivate NO. However, cellular Hb-vesicles (HbV) that encapsulate concentrated Hb solution in phospholipid vesicles (37) ind...

Friction is an important subject for sustainability due to problems that are associated with energy loss. In recent years, micro- and nanostructured surfaces have attracted much attention to reduce friction; however, suitable structures are still under consideration. Many functional surfaces are present in nature, such as the friction reduction surfaces of snake skins. In this study, we focused on firebrats, Thermobia domestica, which temporary live in narrow spaces, such as piled papers, so their body surface (integument) is frequently in contact with surrounding substrates. We speculate that, in addition to optical, cleaning effects, protection against desiccation and enemies, their body surface may be also adapted to reduce friction. To investigate the functional effects of the firebrat scales, firebrat surfaces were observed using a field-emission scanning electron microscope (FE-SEM) and a colloidal probe atomic force microscope (AFM). Results of surface observations by FE-SEM revealed that adult firebrats are entirely covered with scales, whose surfaces have microgroove structures. Scale groove wavelengths around the firebrat’s head are almost uniform within a scale but they vary between scales. At the level of single scales, AFM friction force measurements revealed that the firebrat scale reduces friction by decreasing the contact area between scales and a colloidal probe. The heterogeneity of the scales’ groove wavelengths suggests that it is difficult to fix the whole body on critical rough surfaces and may result in a “fail-safe” mechanism.

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