Micromixing crowded biological agents by folding slugs through pillars

The natural state of the interior of a living cell is extremely dense with numerous molecules packed into a tiny amount of space. Such a physiological environment is known as “crowded” and can exert profound effects on the thermodynamic and kinetic properties of the molecules. In general most biochemical experiments involve low molecular concentrations and in the process, underestimate many reaction rates. This paper reports work on a microfluidic system fabricated using polydimethylsiloxane, and relied on chaotic advection to rapidly mix crowded biological solutions that have been isolated in droplets (slugs). By forcing the slugs through a pillar matrix, the slugs were compelled to stretch and fold repeatedly, creating unsteady fluid flows that rapidly mixed the slug contents in tens of milliseconds at Reynolds number in the order of 10−3. Both straight and serpentine channels containing pillars were used for mixing the slug contents. Our results suggested that the pillars generated a significant amount of interfacial stresses on the slugs and in the process induced rapid mixing. This makes the system suitable for the study of reaction kinetics, which requires reactants to be mixed faster than the actual reaction time itself.