Complex pattern formation in solutions of protein and mixed salts using dehydrating sessile droplets
2020
A sessile
droplet of a complex fluid exhibits several stages of
drying leading to the formation of a final pattern on the substrate.
We report such pattern formation in dehydrating droplets of protein
(BSA) and salts (MgCl2 and KCl) at various concentrations
of the two components (protein and salts) as part of a parametric
study for the understanding of complex patterns of dehydrating biofluid
droplets (blood and urine), which will eventually be used for diagnosis
of bladder cancer. The exact analysis of the biofluid patterns will
require a rigorous parametric study; however, the current work provides
an initial understanding of the effect of the basic components present
in a biofluid droplet. Arrangement of the protein and the salts, due
to evaporation, leads to the formation of some very distinctive final
structures at the end of the droplet lifetime. Furthermore, these
structures can be manipulated by varying the initial ratio of the
two components in the solution. MgCl2 forms chains of crystals
beyond a threshold initial concentration of protein (>3 wt %).
However,
the formation of such a crystal is also limited by the maximum concentration
of the salt initially present in the droplet (≤1 wt %). On
the other hand, KCl forms dendritic and rectangular crystals in the
presence of BSA. The formation of these crystals also depends on the
relative concentration of salt and protein in the droplet. We also
investigated the dried-out patterns in dehydrating droplets of mixed
salts (MgCl2 + KCl) and protein. The patterns can be tuned
from a continuous dendritic structure to a snow-flake type structure
just by altering the initial ratio of the two salts in the mixture,
keeping all other parameters constant.
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