Numerical study of the formation and drying kinetics of a capillary bridge of trehalose solution between two parallel hydrophilic fibres

Abstract

Formation and vitrification of the capillary bridges is believed critical to matrix assisted room temperature drying of biologics. In this paper, a Capillary Bridge number (CB number) is derived to predict the wetting morphology with CB > 0 to form capillary bridges, otherwise, form droplets. To simulate the drying of the formed capillary bridge with pure water or trehalose solution, a continuum model is constructed to predict its surface instability and solute distribution. For the evaporation of a pure water capillary bridge, the numerical simulation results demonstrate that liquid is driven by capillary pressure from the central area to the sides, which eventually triggers the rupture. During the drying of trehalose solution-loaded capillary bridges, Marangoni flow overcomes the capillary flow and pushes liquid towards the centre instead, resulting in solidification except for the very dilute solutions. The results improve understanding and design of matrix assisted room temperature drying of biotherapeutics.