人体血液液滴蒸发诱导的表面壳层失稳及其裂纹图案形成机理

The dried patterns of human blood droplets are significantly influenced by the components of the blood drops, and therefore are closely relative to human health condition. Contrast to the simplicity in phenomenology, the evaporation process is extremely complex because of the coupling of thermodynamics and mechanics involved in. Based on the dried blood patterns, it is possible to develop simple but effective diagnosis method, which is of great importance for medical science and health care. Until now, some tentative results on the characterization of these dried patterns have been reported; however, the underlying mechanisms responsible for pattern formation are still not clear. Therefore, the proposed project will study systematically the drying process and the pattern formation of the droplets of human blood, which will be taken from both healthy persons and those are suffering anemia diseases. By using the techniques of in-situ video microscopy, high speed camera and quartz crystal microbalance, etc, various processes will be investigated, including the wetting behaviors of human blood droplets, evolution of droplet profile, the formation and instability of crust induced by evaporation, the nucleation and propagation of cracks. The project aims to build a complete physical picture for the evaporation of human blood droplets, which links the phenomena of wetting, stress generation, crust formation and instability, and cracking. We focus on how the drop shape evolution, stress field, crack growth and crust buckling are influenced by the blood cells which are regarded as soft colloids. As a result, the mechanisms for the crack nucleation and its pattern formation will be clarified. The link between evaporation patterns with diseases and experimental factors will be revealed, through the analysis of stress field, mass transportation and the mechanical properties of the dried film or crust. The proposed project will elucidate the physical mechanism responsible for the drying pattern formation of human blood droplet. Particularly, the link between dried patterns of blood droplets and anemia diseases will be built. The coupling mechanism between thermodynamics and mechanics in the drying blood droplet will be clarified and the mechanics model for evaporation pattern formation will be established, therefore, providing a reference for the diagnosis of relative diseases.

血液的蒸发图案包含着重要的生理信息，可为某些疾病的诊断提供重要参考。然而，血滴的蒸发过程涉及到复杂的热力学-力学耦合。目前，人们对血液蒸发图案的形成规律及其力学机制尚不清楚，极大阻碍了血液蒸发理论的建立及应用。本项目以人体血液为研究对象，采用实验与数值模拟相结合的方法，以高速显微摄影、石英微晶天平技术为主要手段，研究液滴在不同基底上的润湿行为，探索蒸发应力导致的表面壳层失稳和裂纹扩展；建立跨时间尺度和空间尺度的物理图像，将液滴润湿、蒸发应力产生、壳层失稳、裂纹扩展等不同尺度的物理过程相联系，构建描述血液蒸发的跨尺度力学模型，揭示含有柔性颗粒(血细胞)胶体体系的蒸发图案形成机制；对健康人和贫血病患者的血样进行对比分析，研究患者血滴蒸发所呈现的特殊力学行为及其蒸发图案，揭示其中的力学机制。项目将阐明人体血液液滴蒸发的热力学-力学耦合机制，构建其蒸发图案形成的力学模型，为相关疾病诊断提供借鉴。

人体血液作为人体重要的组织，是复杂的非牛顿流体，其蒸发动力学规律在材料制备、医疗诊断与生物技术等方面具有重要意义。在此背景下，本项目研究了基底性质和酸碱盐的添加对非生物胶体以及人体血液蒸发动力学的影响规律及物理机理，探索了声悬浮条件下非生物胶体以及人体血液液滴的形貌演变规律，得到了以下主要结果：.1.研究了超疏水基底上胶体液滴的蒸发，发现蒸发可导致液滴表面颗粒壳层失稳，表面壳层的失稳形貌与液滴内含胶粒的润湿性存在显著的依赖关系，该结论为研究人体血液液滴的蒸发动力学提供借鉴。.2.声悬浮技术实现了液滴的无容器接触蒸发模式，通过声场计算和对液滴表面蒸发通量的理论分析，得到了液滴不同位置的蒸发速率，揭示了胶体液滴内陷形成的物理机制，阐明了声场力学效应与热力学蒸发的耦合机制，为利用声悬浮技术开展软物质物理研究提供借鉴。.3.研究了基底性质和溶液pH值对人体血液液滴蒸发过程及形貌的调控规律，粗糙基底会减弱血液液滴蒸发时的“咖啡环效应”，并消除裂纹。溶液的PH值会增强或抑制“咖啡环效应”，改变蒸发裂纹的方向和形貌。.4.研究了人体血液液滴在声悬浮条件下的蒸发，研究结果表明，声悬浮条件下血液液滴的蒸发形貌与蒸发过程中液滴的形状有关。随着蒸发的进行，血液中的水分减少，液滴表面形成凝胶层。液滴各个部位所受声辐射力并不相同，中间大于边缘，使得动态平衡下液滴边缘厚度大于中心部位，形成面包圈状结构。.蒸发过程中声辐射力造成的压力沿液滴径向方向，这样外环部分没有大的应力释放，没有裂纹出现。中心部分声辐射力较大，产生上下挤压液滴的作用，出现了较大的十字形裂纹。.该项目揭示了基底性质和溶液pH值对胶体及人体血液液滴蒸发动力学的调控规律，建立了液滴蒸发裂纹扩展的力学模型，发现了声悬浮条件下胶体和血液液滴的受力和形变规律，为进一步研究软物质的蒸发动力学提供借鉴。

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