Droplets-based millifluidic for the rapid determination of biopolymers phase diagrams

Abstract Liquid-liquid phase separation is a phenomenon occurring spontaneously upon changing the physico-chemical conditions of (bio-)polymers mixtures such as pH, ionic strength, total concentration, mixing ratio or temperature. The establishment of a phase diagram is a useful approach to highlight interactions and phase separation conditions of a mixture. Such approach generally performed in bulk is highly time and raw material consuming. In the present work, we developed a droplets-based millifluidic device for rapid phase diagram determination of liquid-liquid phase separated system. The proof of concept was first performed using a colloidal suspension of titanium dioxide (TiO 2 ). The developed millifluidic device was then applied to a model protein-polysaccharide mixture made of β-lactoglobulin (BLG) and Gum Arabic (GA) in water and at pH 4.2. In this model, a specific type of liquid-liquid phase separation occurs: complex coacervation. Biopolymers droplets of about 2.5 μL of various compositions were generated to investigate the impact of total biopolymers concentration (0.1–5 wt %) and protein-polysaccharide mixing ratio (1:8 to 8:1). Initiation and suppression of phase separation were then evidenced through turbidity measurements within the droplets using image analysis. High similarities between cloud points probed using the millifluidic device and the binodal curve determined in bulk were found in the total biopolymers concentration range explored. Droplets-based millifluidic represents an efficient and highly versatile tool to probe liquid-liquid phase separation of various biopolymers mixtures.