Modeling of protein and salt redistribution during drying of a solution from a square cell

Abstract

Background: Drying of biological fluids and saline biopolymer solutions is an actively researched topic, since the textures of the films remaining on the substrate after evaporation carry information about the state of the organism or biopolymer. Earlier, we have shown that the texture area and the amount of zigzag crystallization patterns depend on the structural state of the biopolymer. Models of flows and particle redistribution in a round sessile drop have been described by multiple authors, but in our experiments the solution completely fills a square cell to its walls, which results in different drying conditions and dynamics. Objectives: Conducting a numerical simulation of liquid evaporation and the corresponding redistribution of BSA and NaCl particles for a square 20×1×20 mm3 cell. Materials and methods: Liquid evaporation was simulated in the OpenFOAM continuous media modeling package using the interThermalPhaseChangeFoam module, and the redistribution of the particle concentrations (BSA, Na+ and Cl–) in the solution was simulated using the method of biased random walk on a discrete Cartesian lattice. Results: According to the obtained results, for most of the drying time, the flows in the liquid are from the corners to the center of the cell and from the diagonals to the walls of the cell, which leads to the accumulation of a significant fraction of the particles near the walls. When the liquid-air interface in the central part of the cell reaches the bottom, the surface tension forces quickly withdraw the solution to the cell walls, although a small amount of liquid can remain as a drop in the center. After complete drying, the majority of BSA and NaCl particles that did not settle at the cell walls were found to be concentrated at a distance of 1-3 mm from the cell walls, in the form of a rounded band. A small amount of BSA is also present in the central part of the cell, while the remainder of the salt is uniformly distributed over the entire area of the cell due to its greater diffusivity. Conclusions: Taking into account the experimental distributions of textures, these results support the hypotheses that textures are not formed in the absence of a biopolymer, and that zigzag patterns are formed in locations with high drying rate.