Analysis of flow behavior of blood-biomaterial interfaces

剪切应力是溶血的重要因素，剪切应力是张量值，而溶血水平是标量值。因此。作者提出能量耗散率E （J/m^3）作为剪切应力的广义代入，并对血浆游离血红蛋白给出了如下表达式：H=kE^αt（其中，k和α为常数，H：血红蛋白水平）。此外，由于应力类型（即粘性应力和雷诺数应力）引起的阈值剪切水平的差异，认为仅与暴露时间有关。因此，我们进行了初步的体外溶血试验，以阐明层流和湍流对溶血的影响。在本实验中，使用两种不同粘度的悬浮介质来检测足够宽的雷诺数范围，而不改变红细胞压积或暴露时间。牛红细胞悬浮于生理盐水湍流条件下，悬浮于葡聚糖溶液层流条件下。悬浮液的粘度分别为1.56cP和5.20cP。血液在100-500 Pa剪切应力下循环90 min。计算了Blasius摩擦系数，验证了流动状态是层流还是湍流。实验结果表明，湍流条件下溶血率是层流条件下溶血率的4倍，说明粘性应力和雷诺应力对溶血的影响并不总是相等的。因此，有可能认为能量耗散在预测溶血水平方面起着重要作用。

Shear stress, which is a tensor value, is regarded as an essential factors of hemolysis, but hemolysis level is a scalar value. Therefore. the authors proposed energy dissipation rate E (J/m^3) as a generalized substitute for shear stress and have formulated the following expression for plasma free hemoglobin.H=kE^αt (where, k and α are constant values, H : hemoglobin level)In addition, the difference in the threshold shear level due to the type of stress, namely viscous and Reynolds stress, is believed to be related only to the exposure time. Therefore, preliminary in vitro hemolysis test has been performed using to clarify the effects of laminar and turbulent flows on hemolysis.In the present experiments, two types of suspension media with different viscosities were used to examine a sufficiently wide range of Reynolds numbers without altering hematocrit or exposure time. Bovine red blood cells were suspended in saline for turbulent flow condition and in dextran solution for laminar flow condition. The viscosity of the suspensions were 1.56cP and 5.20cP, respectively. Blood was circulated for 90 min under the shear stress of 100-500 Pa.Blasius friction factor was calculated to verify flow condition as a laminar or turbulent. The experimental results exhibited that hemolysis rate under turbulent flow was four times higher than that under laminar flow, suggesting that the effect of viscous and Reynolds stress on hemolysis is not always equal. Then, it became possible to consider that energy dissipation took an important role to predict a level of hemolysis.