Division of Pharmacy and Optometry, Faculty of Biology, Medicine and Health, The University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PL, U.K.
Institute of Multiscale Thermofluids, School of Engineering, The University of Edinburgh, King's Buildings, James Clerk Maxwell Building, Peter Guthrie Tait Road, King's Buildings, Edinburgh EH9 3FD, U.K.
Langmuir. 2022 Apr 12;38(14):4321-4331. doi: 10.1021/acs.langmuir.2c00019. Epub 2022 Mar 31.
The desiccation of biofluid droplets leads to the formation of complex deposits which are morphologically affected by the environmental conditions, such as temperature. In this work, we examine the effect of substrate temperatures between 20 and 40 °C on the desiccation deposits of fetal bovine serum (FBS) droplets. The final dried deposits consist of different zones: a peripheral protein ring, a zone of protein structures, a protein gel, and a central crystalline zone. We focus on the crystalline zone showing that its morphological and topographical characteristics vary with substrate temperature. The area of the crystalline zone is found to shrink with increasing substrate temperature. Additionally, the morphology of the crystalline structures changes from dendritic at 20 °C to cell-like for substrate temperatures between 25 and 40 °C. Calculation of the thermal and solutal Bénard-Marangoni numbers shows that while thermal effects are negligible when drying takes place at 20 °C, for higher substrate temperatures (25-40 °C), both thermal and solutal convective effects manifest within the drying drops. Thermal effects dominate earlier in the evaporation process leading, we believe, to the development of instabilities and, in turn, to the formation of convective cells in the drying drops. Solutal effects, on the other hand, are dominant toward the end of drying, maintaining circulation within the cells and leading to crystallization of salts in the formed cells. The cell-like structures are considered to form because of the interplay between thermal and solutal convection during drying. Dendritic growth is associated with a thicker fluid layer in the crystalline zone compared to cell-like growth with thinner layers. For cell-like structures, we show that the number of cells increases and the area occupied by each cell decreases with temperature. The average distance between cells decreases linearly with substrate temperature.
生物体液液滴的干燥会导致形成复杂的沉积物，这些沉积物的形态会受到环境条件（如温度）的影响。在这项工作中，我们研究了基底温度在 20 到 40°C 之间对胎牛血清（FBS）液滴干燥沉积物的影响。最终干燥的沉积物由不同区域组成：一个外围蛋白质环、一个蛋白质结构区域、一个蛋白质凝胶和一个中央结晶区域。我们专注于结晶区域，表明其形态和形貌特征随基底温度而变化。发现结晶区域的面积随基底温度的升高而收缩。此外，结晶结构的形态从 20°C 时的树枝状变为 25 到 40°C 之间的细胞状。热和溶质 Bénard-Marangoni 数的计算表明，当干燥发生在 20°C 时，热效应可以忽略不计，但对于较高的基底温度（25-40°C），干燥液滴内会出现热和溶质对流效应。热效应在蒸发过程的早期占主导地位，我们认为这导致了不稳定性的发展，从而在干燥液滴中形成了对流细胞。另一方面，在干燥的后期，溶质效应占主导地位，保持细胞内的循环，并导致形成的细胞中盐的结晶。考虑到干燥过程中热和溶质对流的相互作用，形成了类似细胞的结构。与类似细胞的生长相比，树枝状生长与结晶区较厚的流体层有关。对于类似细胞的结构，我们表明随着温度的升高，细胞的数量增加，每个细胞所占据的面积减小。细胞之间的平均距离随基底温度线性减小。
