Patterns in dried droplets are commonly observed as rings left after spills of dirty water or coffee have evaporated. Patterns are also seen in dried blood droplets and the patterns have been shown to differ from patients afflicted with different medical conditions. This has been proposed as the basis for a new generation of low-cost blood diagnostics. Before these diagnostics can be widely used, the underlying mechanisms leading to pattern formation in these systems must be understood. We analyse the height profile and appearance of dispersions prepared with red blood cells (RBCs) from healthy donors. The red cell concentrations and diluent were varied and compared with simple polystyrene particle systems to identify the dominant mechanistic variables. Typically, a high concentration of non-volatile components suppresses ring formation. However, RBC suspensions display a greater volume of edge deposition when the red cell concentration is higher. This discrepancy is caused by the consolidation front halting during drying for most blood suspensions. This prevents the standard horizontal drying mechanism and leads to two clearly defined regions in final crack patterns and height profile.

This article is part of a discussion meeting issue ‘A cracking approach to inventing new tough materials: fracture stranger than friction’.

干燥液滴中的图案通常是脏水或咖啡蒸发后留下的环。在干燥的血滴中也可以看到图案，并且这些图案已被证明与患有不同疾病的患者不同。这已被提议作为新一代低成本血液诊断的基础。在广泛使用这些诊断方法之前，必须了解导致这些系统中模式形成的潜在机制。我们分析了用健康捐献者的红细胞 (RBC) 制备的分散体的高度轮廓和外观。改变红细胞浓度和稀释剂，并与简单的聚苯乙烯颗粒系统进行比较，以确定主要的机械变量。通常，高浓度的非挥发性组分会抑制环的形成。然而，当红细胞浓度较高时，红细胞悬浮液显示出较大体积的边缘沉积。这种差异是由于大多数血液悬浮液在干燥过程中固结前沿停止造成的。这阻止了标准的水平干燥机制，并导致最终裂纹图案和高度轮廓中出现两个明确定义的区域。

本文是讨论会议问题“发明新坚韧材料的破解方法：比摩擦更奇怪的断裂”的一部分。