The microenvironment of double emulsions in rectangular microchannels

Abstract

The flow environment in inner cores of water-in-oil-in-water (w/o/w) microfluidic double emulsions has a significant impact on industrial applications of such systems. For example, in the case of shear sensitive cells compartmentalised in the cores, high shear conditions may be deleterious. This study reports on the flow characteristics of w/o/w inner cores in comparison to those in single water -in-oil (w/o) microdroplets of equal size moving in the same microchannel, resolved by means of micro -particle image velocimetry (μPIV). The multiphase flow system employed in the study had a viscosity ratio, λ, between aqueous and oil phase of the order of unity (λ = 0.78) and both single droplets and inner cores of double emulsions filled the channel. This configuration resulted in a weak recirculating flow inside the w/o single droplet: the measured flow field exhibited a uniform low velocity flow field in the central region surrounded by small regions of reversed flow near the channel walls. This flow topology was maintained in the inner cores of w/o/w double emulsions for intermediate capillary numbers ( Ca) ranging from 10 -3 to 10 -2 , and core morphologies varying from large plugs to pancake cores. The core morphology affected the magnitude and distribution of the velocity in the droplets. The similarity in the flow topology resulted from the fact that inner cores were located at the back of the outer droplet in such a way that inner and outer interfaces were in contact for over half of core surface area and separated only by a thin lubricating film. Both single droplets and inner cores exhibited a narrow shear rate distribution characterised by small regions of maximum shear confined near the channel walls. Shear rate magnitude values were found to be an order of magnitude lower than those in the channel and hence capable of reducing stresses in flow cytometry to far below reported values for cell damage. Hence, it can be concluded that double emulsions are suitable candidates to substitute single droplets in flow cytometry to protect the screened items and are compatible with the commercial flow cytometry systems.

Monodisperse polyethylene glycol diacrylate hydrogel microsphere formation by oxygen-controlled photopolymerization in a microfluidic device

“…In balancing both [PI] and [R*] convective transport is neglected because [PI] is exposed and converted into radicals evenly across the droplet and [R*] is consumed much faster than it is transported. While it has been clearly established that recirculating three-dimensional flows do form in microdroplets as they flow through a microchannel 61,62 , it was assumed that these interior flows diminish with polymerization, and our experimental results validate this assumption. The oxygen specie balance equation (Equation 3) addresses two events: oxygen-radical scavenging and the diffusive oxygen flux into the droplet.…”

Micro-Particle Image Velocimetry Investigation of Flow Fields of SonoVue Microbubbles Mediated by Ultrasound and Their Relationship With Delivery

“…The velocity gradients were calculated from the measured velocities with the least squares method. Based on the velocity gradients, the shear rates were estimated as ϵ Ma et al, 2015). The shear stress t was calculated as t = hϵ, where h was the fluid viscosity and set to 1.05 ± 0.01 mPa·s (Helfield et al, 2016a).…”

Gel Microrods for 3D Tissue Printing

“…Shear stresses are critical in cell printing, and therefore we performed hydrodynamic simulations in Comsol Multiphysics to explore the microenvironment in GelMa plugs of various viscosities moving at set velocities within the tubing. The simulations show that the strain rates are lower in plugs than in continuous single‐phase flow, and that the reduction in the strain rates is more significant in higher viscosity plugs. After the droplet‐to‐oil viscosity ratio exceeds 50, the droplet interior circulation is mostly suppressed and the strain rates approach zero (Figures S10 and S11, Supporting Information).…”

“…A key consideration in performing cell printing is to reduce the shear stress . Hydrodynamic simulations showed that the shear strains in GelMa plugs are reduced by comparison with single‐phase flow, suggesting that the encapsulated cells are protected (Figures S10 and S11, Supporting Information). Indeed, patterned GelMa microrods containing living cells, including both immortalized and primary cells, showed ≈90% viability and typical cellular behaviors, including migration and proliferation in culture after printing, demonstrating that the shear stress in the tubing, the exposure to oil, the process of phase‐transfer and photo‐crosslinking are compatible with 3D cell culture.…”