Evaluation of the hemolysis and fluid dynamics of a ventricular assist device under the pulsatile flow condition

When the rotary blood pumps are used as ventricular assist devices,the pump flow rate will have a pulsatile component even at a constant impeller rotational speed due to the remaining beating of the natural heart.However,previous studies on the in vitro hemolysis evaluation of a rotary blood pump have always been conducted under steady states and this pulsation was not taken into account.In this study,the hemolysis in a centrifugal blood pump is evaluated under the pulsatile flow condition in vitro.The required time-varying flow rate is obtained by conducting a system simulation of the pump-assisted cardiovascular system,and realized by controlling a pulsation unit in the experiments.The results of our tests indicate a significant increase in hemolysis under the pulsatile flow condition compared with the non-pulsatile condition.To reveal the flow characteristics responsible for the higher hemolysis,transient computational fluid dynamic simulations are then performed.This study suggests that traditional hemolysis evaluation under the steady states may not fully represent the hemolytic performance in the clinical use.For the ventricular assist pumps at the design stage,eliminating the concern about the extra hemolysis under the pulsatile condition will be helpful for the subsequent in vivo experiments.

Shape Memory of Elastic Capsules Under the Effect of Spontaneous Shape

Red blood cells can recover their resting shape after having been deformed by shear flow.Their rims are always formed by the same part of the membranes,and the cells are said to have shapememory.Modeled as two-dimensional elastic capsules,their recoverymotion and shapememory is studied,mainly focused on the effect of the spontaneous shape.The fluid-structure interaction ismodeled using immersed boundary method.Based on the simulations,the resting shapes of capsules are obtained and the area ratio of spontaneous shape is found to play an important role.After remove of shear flow,all capsules can recover their resting shapes,while only capsules with noncircular spontaneous shapes present shape memory.As the spontaneous shape approaches a circle but still noncircular,the capsule spends more time on recovery process.We consider how these capsules deform depending on the membrane bending energy,and find that the relaxation speed is positive correlated to the range of values of dimensionless bending energy.These results may help to identify different spontaneous shapes for capsules especially RBCs through future experiments.