Microhemorheology

这项研究计划的长期目标是在国际努力中发挥作用，开发一种精确的微观血液流动模型。在生理和诊断环境中描述血液流动是必不可少的。血液是一种非常有趣的流体，必须更好地了解它才能服务于许多医疗应用：了解生理、病理以及了解血液如何在医疗设备中流动。血液在微尺度上不能被认为是液体流动，而是一种颗粒的集合：红细胞。红细胞约占血液体积的一半，其余的血液体积被血浆所占据。血液是悬浮液家族中特别复杂的一种：它是一种高度可变形并相互作用的致密颗粒悬浮液，例如，它们可以聚集在一起。我们对血液的流变学感兴趣，因为这是其力学的基础：它是力和位移之间的纽带。可以追溯到20世纪70年代的大量研究结果表明，血液是一种剪切稀化流体，即其表观粘度随着切变率的增加而降低。然而，这种总体描述不能预测血液在微观尺度上的行为，因为在这种情况下，局部粘度取决于许多其他因素，例如局部剪切、细胞密度或细胞彼此或与壁的相互作用。此外，这个整体模型不能用来理解或预测气体、营养或药物的局部转移。已有研究表明，流动中红细胞(或红细胞压积)的局部密度是不恒定的，例如，流动中的一些区域几乎没有红细胞，包括靠近管壁的区域和高浓度区域，特别是在血管中心或分叉处。细胞的相互作用和强烈的异质性，虽然在70年代就已经被观察到，但从未被包括在血液的流变学模型中。近年来，悬浮液流变学领域取得了很大的进展，这凸显了局部颗粒密度的重要性。关于血液，现在是将流变学测量与局部微结构表征结合起来的时候了。依靠世界级的高度专门化的设备，以及我们实验室开发的独创实验程序，并受益于强有力的国际合作，我们的目标是研究微循环中的细胞运输，重点是与微结构相关的血流特征。特别是，我们的目标是研究受限流动和网络中红细胞的集体动力学，以用于健康和病理细胞的模型。

The long-term goal of this research program is to fulfill a role in the international efforts to develop a precise model of microscopic blood flow. It is essential to describe blood flow in both physiological and diagnostic settings. Blood is a very interesting fluid that must be better understood to serve many medical applications: understanding physiology, pathology as well as understanding how blood flows in medical devices. The blood at the microscale cannot be considered as liquid flow, but rather as a collection of particles: the red blood cells (RBCs). The RBCs represents approximately half of the volume of the blood and the rest of the volume of the blood is occupied by plasma. Blood is in the family of suspensions particularly complex: it is a dense suspension of particles that are highly deformable and interact with each other, for example, they can aggregate. We are interested in the rheology of blood because this is the foundation of its mechanics: it is the link between force and displacements. Great results are dating back to the 1970s that show that blood is a shear-thinning fluid i.e. its apparent viscosity decreases when shear rate increases. However, this overall description cannot predict the blood behavior at the microscale because in this circumstance the local viscosity depends on many other factors such as local shear, cell density or cells interaction with each other or with the walls. Besides this overall model cannot be used to understood or predict local transfers of gas, nutriment or drugs. It has been shown that the local density of red blood cells (or hematocrit) is inconstant in the flow, for example there are areas of the flow where there is almost no red blood cell including close to the walls and areas of high concentration especially in the center of the vessel or at the bifurcations. The interactions of the cells and the strong heterogeneities, although already observed in the '70s, have never been included in the rheological modeling of the blood. Recently, great progress has been made in the field of suspension rheology, which highlights the importance of the local particle density. Regarding blood, it is time to couple the rheological measurements with the characterization of local microstructures. Relying on world-class highly-specific equipment, along with original experimental procedures developed in our laboratory and benefiting of strong international collaborations, our goal is to study cellular transport in the microcirculation focusing on the characterization of blood flow in relation to microstructure. In particular, we aim to study the collective dynamics of red blood cells in confined flows and networks, for healthy and model of pathological cells.