In this study, we
analyze stain growth kinetics from droplets of
biological fluids such as blood, plasma, and protein solutions on
paper both experimentally and numerically. The primary difference
of biological fluids from a simple fluid is a significant wetting/dewetting
hysteresis in paper. This becomes important in later stages of droplet
wicking, after the droplet has been completely absorbed into paper.
This is shown by anomalous power dependence of area with time in the
later stages of radial wicking. At early stages, current numerical
wicking models can predict stain growth of biological fluids. However,
at later stages, the introduction of hysteresis complicates modeling
significantly. We show that the cause of the observed hysteresis is
due to contact angle effects and that this is the dominant mechanism
that leads to the anomalous stain growth kinetics measured uniquely
in biological fluids. Results presented will streamline the design
process of paper-based diagnostics, allowing a modeling approach instead
of a trial and error method.
Paper-based diagnostics are leading the field of low-cost, point of care analytical techniques. However, large scale testing facilities such as hospitals are still primarily using the gel column agglutination technique....
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’.
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