Modeling of spatial–temporal distribution of the components in the drying sessile droplet of biological fluid

• Final shape of the droplet is a doughnut. • Proteins accumulate near the edge of the dried drop. • Salts are distributed uniformly across the diameter of the dried drop. Using lubrication theory, drying processes of sessile droplets of blood serum (i.e. colloids with the salt admixture) on a solid hydrophilic horizontal substrate are studied. The concentration of the solute is supposed to be high enough to ensure good adhesion and strong anchoring (pinning) of the triple line, thereby a drop is desiccating with constant base. The simulation of spatial distribution of the components in the droplet of biological fluid drying on a substrate is performed using advection–diffusion equation. The proposed model explains the redistribution of components in a sessile drop of biological fluid when it dries. Competition between advection and diffusion leads to large particles (protein) accumulating at the edge of the drop (well-known coffee-ring effect), while solutes (salts) are distributed more uniformly across the diameter of the sample.