Abstract
HypothesisThe process of dried blood spot sampling involves simultaneous spreading and penetration of blood into a porous filter paper with subsequent evaporation and drying. Spreading of small drops of blood, which is a non-Newtonian liquid, over a dry porous layer is investigated from both theoretical and experimental points of view. Experiments and theoryA system of two differential equations is derived, which describes the time evolution of radii of both the drop base and the wetted region inside the porous medium. The system of equations does not include any fitting parameters. The predicted time evolutions of both radii are compared with experimental data published earlier. FindingsFor a given power law dependency of viscosity of blood with different hematocrit level, radii of both drop base and wetted region, and contact angle fell on three universal curves if appropriate scales are used with a plot of the dimensionless radii of the drop base and the wetted region inside the porous layer and dynamic contact angle on dimensionless time. The predicted theoretical relationships are three universal curves accounting satisfactorily for the experimental data.
Highlights
Dried blood spot (DBS) sampling is a method of blood collection, transportation and storage which has been investigated and used over the recent decades [1,2,3,4,5,6]
The whole process can be subdivided into two stages as in the case of Newtonian liquids [21]: over duration of the first stage, the expansion of droplet radius, due to the capillary regime of spreading, is faster than the shrinkage, due to the imbibition into the filter paper, until they counterbalance themselves as the maximum radius is reached
A system of two differential equations is derived from the combination of the model of spherical cap spreading over porous layer [21] and a modified Darcy’s law for power law fluids
Summary
Dried blood spot (DBS) sampling is a method of blood collection, transportation and storage which has been investigated and used over the recent decades [1,2,3,4,5,6]. In [21] the spreading of Newtonian liquid over dry porous substrates was investigated in the case of complete wetting. Spreading of droplets of non-Newtonian liquids over smooth solid surfaces was considered in [22] in the case of complete wetting. The liquid under investigation is spreading/imbibition of a blood drop, which is a non-Newtonian power-law liquid, over a filter paper. The problem under investigation is similar to that considered in [21] when a drop of Newtonian liquid spreads over a dry porous layer, the difference is that the liquid is a non-Newtonian blood. Spreading of ‘‘big drops’’, that is, bigger as compared with thickness of the porous substrate but still small enough to neglect the gravity action over ‘‘thin porous layers’’ is considered below
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