A platform for studying the role of haemodynamics in microvascular disease

为了发挥作用，体内的所有细胞都需要定期供应氧气和不断清除废物。两者都是由通过微血管系统输送的血液提供的，微血管系统包括直径小于0.1 mm的血管。为了实现其功能，血液的流动必须严格控制。这种调节的一个关键组成部分是排列在所有微血管中的专门的“内皮细胞”。这些细胞感受到流动的血液产生的摩擦力，并作为响应释放化学物质，这些化学物质可以增加或减少血管的大小，以帮助调节流动。当这一规定失败时，结果可能是毁灭性的。例如，血流失调是糖尿病视网膜病变的第一阶段之一，这种疾病威胁着世界上1%成年人口的视力。因此，了解血液在微血管中流动的细节非常重要。影响微血管血流的主要因素是红细胞（RBC）的机械性质。红细胞是高度可变形的，这使得它们在较大的血管中流动时可以变形，甚至可以通过比其直径小得多的毛细血管。红细胞也有粘在一起的倾向，在一个称为聚集的过程中，这取决于局部流动特征。由于这些红细胞的行为，微血管中的血液流动是复杂的，人们对其知之甚少。这一点特别重要，因为在许多微血管疾病中，包括糖尿病，红细胞变得比健康个体更不易变形和聚集。这些变化已被证明与疾病进展相关，但尚未确切确定血液特性的变化如何影响微血管功能。我们假设红细胞特性的变化改变了血流，从而改变了内皮细胞所经历的摩擦力，这反过来又导致了血流失调，最终损害了微血管系统。在这个项目中，我们将使用最先进的实验技术来直接评估红细胞特性的变化如何影响微尺度血流。一个关键的挑战是微血管网络的复杂分支模式。这些网络由不同大小、结构和功能的血管组成，其中红细胞流量和浓度都发生显著变化。为了提高我们对血液如何在微血管中流动的认识，我们需要能够测量红细胞的速度及其在给定血管或微血管网络部分中的局部浓度。我们将使用最近开发的光学技术来实现这一目标，将通过血液样本的光的测量与添加到血浆中的微粒的荧光测量相结合。获取这两个参数可以计算血管壁上的摩擦力，并将其与数值模型生成的结果进行比较。目前还不可能在人类或活体动物中进行这些测量，因此我们将使用一种新技术来构建逼真的微血管模型，其中激光能量用于降解水凝胶，留下可以精确控制的血管结构。我们将使健康志愿者的血液流过这些模型，并测量各种条件下的流动和壁摩擦。然后，我们将对血液样本进行化学处理，以模拟糖尿病中发生的变化，并测量相应的血流变化。除了提供对血流的新见解外，这项研究中产生的证据还将揭示血液机械特性的变化如何影响糖尿病等疾病。从长远来看，这一见解有望为诊断和治疗微血管疾病带来新的方法。

In order to function, all cells in the body require a regular supply of oxygen and continuous removal of waste products. Both are provided by blood delivered through the microvasculature, which comprises vessels smaller than 0.1 mm in diameter. In order to fulfil its function, the flow of blood must be tightly regulated. A key component of this regulation are the specialist 'endothelial cells' that line all microvessels. These cells sense frictional forces arising from the flowing blood and in response release chemical substances that can increase or decrease the size of the vessels to help regulate the flow. When this regulation fails, the results can be devastating. For example, dysregulation of blood flow is one of the first stages in diabetic retinopathy, a condition that threatens the sight of 1% of the world's adult population. It is therefore important to understand the details of how blood flows in microvessels. A major factor that influences microvascular blood flow is the mechanical properties of red blood cells (RBCs). RBCs are highly deformable, which allows them to deform while flowing in larger vessels and even fit through capillaries much smaller than their diameter. RBCs also have a propensity to stick together, in a process called aggregation that is dependent on local flow characteristics. As a result of these RBC behaviours, the flow of blood in microvessels is complex and poorly understood. This is particularly important, because in numerous microvascular diseases, including diabetes, the RBCs become less deformable and aggregate more than in healthy individuals. These changes have been shown to correlate with disease progression, but it has not yet been established exactly how changes to blood properties affect microvascular function. We hypothesise that the changes in RBC properties alter blood flow and hence the frictional forces experienced by the endothelial cells, which in turn leads to dysregulation of flow and ultimately damage to the microvasculature. In this project, we will use state-of-the-art experimental technology to directly evaluate how changes to RBC properties affect microscale blood flow. A key challenge is the complicated branching patterns of the microvessel network. These networks consist of vessels of different sizes, structure and functions, throughout which both RBC flow and concentration change significantly. In order to improve our knowledge of how blood flows in microvessels, we need to be able to measure both the velocity of the RBCs and their local concentration in a given blood vessel or section of a microvascular network. We will achieve this using recently developed optical techniques, combining measurements of light passing through a blood sample with fluorescence measurements of microparticles added to the plasma. Acquiring both of these parameters allows calculation of the frictional forces on the vessel wall, which will be compared to results generated with numerical models. It is not currently possible to make these measurements in humans or living animals, hence we will build realistic models of microvessels using a new technique where laser energy is used to degrade a hydrogel, leaving behind a vessel structure that can be precisely controlled. We will flow blood from healthy volunteers through these models and measure the flow and wall friction under various conditions. We will then chemically treat the blood samples to mimic changes that occur in diabetes and measure the corresponding changes in flow. In addition to providing new insight into blood flow, the evidence generated in this study will reveal how changes to blood mechanical properties might affect diseases such as diabetes. In the long term, this insight is expected to lead to new approaches for diagnosing and treating microvascular diseases.