It is well known that red blood cells(RBCs)are suffered from chronic stresses in systemic circulation. The objective of this study is to clarify the effect of the aging of RBCs on rheological properties and hemolysis. Initially, RBCs age fractionation was performed by using a high-speed centrifugation(15[min]at1500[G]), then young and aged RBCs were suspended in plasma to adjust the hematocrit level of40[%]. After this pretreatment, the viscosity was measured by using a capillary type and a cone-plate type viscometers, respectively, and the hemolysis test was carried out by a seesaw type shaker. Results from these experiments showed that the viscosity of young RBCs measured by the capillary viscometer was increased by 10[%]as compared with that of aged RBCs.Under the condition of all shear zones, the viscosity was increased in case of using the cone-plate type viscometer. And the hemolytic level was increased twice as the aging. The data obtained in this study indicated that the ability of aggregation of RBCs was increased and the deformability of RBCs' membrane got lower with the aging. Furthermore, it was exhibited that the fragility of RBCs'membrane was increased with the aging.

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Microcapsule suspensions substituted for animal blood were designed as model blood for hemolysis tests of circulatory artificial organs. They included microcapsules, which were likened to erythrocytes, for main components of the suspensions .In this paper, we used two types of microcapsules, whose membrane materials were polyurethane and melamine resin respectively, and the both target sizes were 100μm in diameter. The fractural properties of the capsules in the suspensions were tested under the shear stress, generated by the rotational shear stressor. Flow patterns in the shear stressor were examined with an oil spot method. Polyurethane-capsule suspension showed similar fractural behavior to the bovine blood results under the rotational shear stressor. However, the behavior of melamine-capsule suspensions was different from the bovine blood, though the destructive sensitivity was higher than that of polyurethane-capsule suspension. We conclude that both suspensions with 100μm diameter can be candidates of standard hemolysis test solutions.

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Hemolysis is one of important factors in developing rotary blood pumps. It is, however, difficult to identify the areas where hemolysis occurs. Computational fluid dynamics(CFD)analysis enables the engineer to predict hemolysis on a computer. In this study fluid dynamics were analyzed in a wholer region of the intra-cardiac axial flow pump. Reynolds shear stresses were computed along particle trace lines. Hemolysis was evaluated based on the shear stress(τ)and its exposure time(Δt): dHb/Hb=3.62×10^-7τi^2.416×Δti^0.785. Particle damage was accumulated with time along the particle trace lines. The computed hemolysis values were compared with experimental results. The hemolysis characteristic results were in good agreement with the CFD values. CFD is a very powerful tool to develop rotary blood pumps.

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Closing response of the mechanical heart valve prostheses was evaluated using an X-ray high-speed video camera and a mechanical mock circulator. Effect of the valve design parameters, such as designed angle at closed position; momentum of inertia and mass of occluder, on the closing response was examined. The closing response was analyzed by the following parameters;(1)pressure gradient at onset of valve closing, (2)amount of back flow volume during motion, (3)period during closing motion. It was clarified that 1)back flow volume and a period during closing motion were closely influenced by an angle of closed position, while pressure gradient was changed by the mass of occluder, 2)there was no distinct change in closing response, when a momentum of inertia was varied up to 78×10^-9kg⋅m².

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