Selective flow-induced vesicle rupture to sort by membrane mechanical properties

International audienceVesicle and cell rupture caused by large viscous stresses in ultrasonication is central to biomedical and bioprocessing applications. The flow-induced opening of lipid membranes can be exploited to deliver drugs into cells, or to recover products from cells, provided that it can be obtained in a controlled fashion. Here we demonstrate that differences in lipid membrane and vesicle properties can enable selective flow-induced vesicle break-up. We obtained vesicle populations with different membrane properties by using different lipids (SOPC, DOPC, or POPC) and lipid:cholesterol mixtures (SOPC:chol and DOPC:chol). We subjected vesicles to large deformations in the acoustic microstreaming flow generated by ultrasound-driven microbubbles. By simultaneously deforming vesicles with different properties in the same flow, we determined the conditions in which rupture is selective with respect to the membrane stretching elasticity. We also investigated the effect of vesicle radius and excess area on the threshold for rupture, and identified conditions for robust selectivity based solely on the mechanical properties of the membrane. Our work should enable new sorting mechanisms based on the difference in membrane composition and mechanical properties between different vesicles, capsules, or cells

Surface waves on a soft viscoelastic layer produced by an oscillating microbubble

Ultrasound-driven bubbles can cause significant deformation of soft viscoelastic layers, for instance in surface cleaning and biomedical applications. The effect of the viscoelastic properties of a boundary on the bubble-boundary interaction has been explored only qualitatively, and remains poorly understood. We investigate the dynamic deformation of a viscoelastic layer induced by the volumetric oscillations of an ultrasound-driven microbubble. High-speed video microscopy is used to observe the deformation produced by a bubble oscillating at 17-20 kHz in contact with the surface of a hydrogel. The localised oscillating pressure applied by the bubble generates surface elastic (Rayleigh) waves on the gel, characterised by elliptical particle trajectories. The tilt angle of the elliptical trajectories varies with increasing distance from the bubble. Unexpectedly, the direction of rotation of the surface elements on the elliptical trajectories shifts from prograde to retrograde at a distance from the bubble that depends on the viscoelastic properties of the gel. To explain these behaviours, we develop a simple three-dimensional model for the deformation of a viscoelastic solid by a localised oscillating force. By using as input for the model the values of the shear modulus obtained from the propagation velocity of the Rayleigh waves, we find good qualitative agreement with the experimental observations

Shear-induced deformation of surfactant multilamellar vesicles

Surfactant multilamellar vesicles (SMLVs) play a key role in the formulation of many industrial products, such as detergents, foodstuff, and cosmetics. In this Letter, we present the first quantitative investigation of the flow behavior of single SMLVs in a shearing parallel plate apparatus. We found that SMLVs are deformed and oriented by the action of shear flow while keeping constant volume and exhibit complex dynamic modes (i.e., tumbling, breathing, and tank treading). This behavior can be explained in terms of an excess area (as compared to a sphere of the same volume) and of microstructural defects, which were observed by 3D shape reconstruction through confocal microscopy. Furthermore, the deformation and orientation of SMLVs scale with radius R in analogy with emulsion droplets and elastic capsules (instead of R3, such as in unilamellar vesicles). A possible application of the physical insight provided by this Letter is in the rationale design of processing methods of surfactant-based systems

Mixing of Liquid-liquid Non-Newtonian Fluids, Preliminary Results

Immiscible liquid-liquid suspensions, such as emulsions and polymer blends, are frequently encountered in a variety of applications, e.g., cosmetics and pharmaceuticals design, food processing, plastics technology. Mixing efficiency of such systems is greatly influenced by the property of the two phases, most of the fluids used by the industry show Non-Newtonian behavior. This work is concerned with the application of static mixers to form biphasic liquid dispersions in the laminar flow regime; in particular we present here a methodology to investigate the effect on the mixing efficiency of elasticity of one phase. To this aim, two low viscosity Boger fluids, obtained by mixing small amount of Polyacrilamide and Xantan gum in a Newtonian glycerin-water solvent, were used as aqueous phase and mixed with silicon oils of different molecular weight. In order to quantify the influence of viscoelasticity on the mixing efficiency, a reference Newtonian fluid (GLY) obtained by mixing water and glycerin in an appropriate concentration to obtain the same viscosity of the non-Newtonian reference was used. The mixing efficiency has been quantified by measuring the drop size distribution by optical microscopy and image analysis. The expected influence of the elasticity is to delay break-up phenomena, so resulting in a lower mixing efficiency, the effect is expected to be limited when the elasticity is only in the drop phase, compared to the case of elastic matrix. Below the drop size distribution for the case of aqueous disperse phase in SO is reported; on the left graph the numerical distribution is compared for Newtonian GLY and non-Newtonian XGh and PAA, on the right one the cumulative volumetric shows that the differences are limited to the large diameter tail of the distribution, that represents most of the dispersed phase volume