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

Pommella A, Brooks NJ, Seddon JM, Garbin V - Sci Rep (2015)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical Engineering, Imperial College London, London SW7 2AZ, United Kingdom.

ABSTRACT
Vesicle 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.

No MeSH data available.


Related in: MedlinePlus

Selectivity of flow-induced vesicle break-up for single-component membranes.(a) SOPC (fluorescent) against DOPC. Frames (i–vi) show no selectivity, as vesicles from both populations break in the microstreaming flow. The graph compares the critical capillary numbers (horizontal lines) and stretching elasticities (vertical lines) for SOPC (dashed lines) and DOPC (solid lines). For R ≈ 30 μm  for both SOPC and DOPC. (b) SOPC (fluorescent) against POPC. Break-up is selective, as all SOPC vesicles with R > 15 μm break, while most POPC vesicles remain intact in frames (i–vi). The graph shows that  only for SOPC vesicles (dashed lines) but not for POPC vesicles (solid lines). All images are in top view.
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f2: Selectivity of flow-induced vesicle break-up for single-component membranes.(a) SOPC (fluorescent) against DOPC. Frames (i–vi) show no selectivity, as vesicles from both populations break in the microstreaming flow. The graph compares the critical capillary numbers (horizontal lines) and stretching elasticities (vertical lines) for SOPC (dashed lines) and DOPC (solid lines). For R ≈ 30 μm for both SOPC and DOPC. (b) SOPC (fluorescent) against POPC. Break-up is selective, as all SOPC vesicles with R > 15 μm break, while most POPC vesicles remain intact in frames (i–vi). The graph shows that only for SOPC vesicles (dashed lines) but not for POPC vesicles (solid lines). All images are in top view.

Mentions: To test the selectivity of vesicle break-up with respect to the mechanical properties of the membrane, we simultaneously deformed vesicles with different lipid composition in the same acoustic microstreaming flow. Figure 2a shows an experiment where pure SOPC vesicles are compared with pure DOPC vesicles. The SOPC vesicles are fluorescently labelled (see Methods), while the DOPC vesicles are not fluorescent. Frames (i-ii) in Fig. 2a show the configuration of vesicles around the bubble before the microstreaming flow is activated (pA = 0 kPa). The phase contrast image in frame (i) shows several vesicles ranging in radius from a few microns up to 25 μm. The fluoresence image in frame (ii) shows only the SOPC vesicles. When the microstreaming flow is activated, with an acoustic pressure pA = 14 kPa, the vesicles are slightly deformed as shown in frame (iii). Increasing the acoustic pressure to pA = 22 kPa causes significant deformation and rupture of the vesicles as shown in frame (iv). Frames (v-vi) show the configuration after the microstreaming flow has stopped (pA = 0 kPa). SOPC and DOPC vesicles larger than 15μm have ruptured, and only small SOPC and DOPC vesicles are present. Small vesicles can either be the product of the break-up of larger vesicles, or they were initially present and have not ruptured. These observations are consistent with the magnitudes of the capillary numbers, , and the critical capillary numbers, , for SOPC and DOPC membranes. The graph in Fig. 2a reports the capillary number, CaK = ηGmaxR/KA, as a function of KA, for two different vesicle radii, R = 15μm and R = 30μm. The other parameters are representative of typical conditions in the experiments, i.e., a characteristic stress τmax = ηGmax ≈ 100 Pa. For the experiments of Fig. 2, it is not possible to obtain τmax from Eq. (1), because the bubble oscillations are non-linear. Estimates of τmax that motivate the assumption made here are provided later in the paper. The horizontal lines represent the values of the critical capillary number, , for SOPC (dashed line) and DOPC (solid line). The critical capillary number depends only on the properties of the membrane, and not on the vesicle size or the flow conditions. For vesicles with R = 30 μm, the capillary numbers for both SOPC and DOPC vesicles exceed the respective thresholds for break-up (solid circles). For radii R = 15μm and smaller, both SOPC and DOPC vesicles exhibit capillary numbers below the respective thresholds for break-up (open circles). We observed approximately 10 SOPC vesicles and 20 DOPC vesicles, and found probabilities of break-up of vesicles larger than 15 μm in the same flow conditions of 70% and 65%, respectively. Because SOPC and DOPC vesicles present similar values of stretching elasticity, KA, and of the critical capillary number (see Table 1), selective break-up of only one population is not possible.


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

Pommella A, Brooks NJ, Seddon JM, Garbin V - Sci Rep (2015)

Selectivity of flow-induced vesicle break-up for single-component membranes.(a) SOPC (fluorescent) against DOPC. Frames (i–vi) show no selectivity, as vesicles from both populations break in the microstreaming flow. The graph compares the critical capillary numbers (horizontal lines) and stretching elasticities (vertical lines) for SOPC (dashed lines) and DOPC (solid lines). For R ≈ 30 μm  for both SOPC and DOPC. (b) SOPC (fluorescent) against POPC. Break-up is selective, as all SOPC vesicles with R > 15 μm break, while most POPC vesicles remain intact in frames (i–vi). The graph shows that  only for SOPC vesicles (dashed lines) but not for POPC vesicles (solid lines). All images are in top view.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4548244&req=5

f2: Selectivity of flow-induced vesicle break-up for single-component membranes.(a) SOPC (fluorescent) against DOPC. Frames (i–vi) show no selectivity, as vesicles from both populations break in the microstreaming flow. The graph compares the critical capillary numbers (horizontal lines) and stretching elasticities (vertical lines) for SOPC (dashed lines) and DOPC (solid lines). For R ≈ 30 μm for both SOPC and DOPC. (b) SOPC (fluorescent) against POPC. Break-up is selective, as all SOPC vesicles with R > 15 μm break, while most POPC vesicles remain intact in frames (i–vi). The graph shows that only for SOPC vesicles (dashed lines) but not for POPC vesicles (solid lines). All images are in top view.
Mentions: To test the selectivity of vesicle break-up with respect to the mechanical properties of the membrane, we simultaneously deformed vesicles with different lipid composition in the same acoustic microstreaming flow. Figure 2a shows an experiment where pure SOPC vesicles are compared with pure DOPC vesicles. The SOPC vesicles are fluorescently labelled (see Methods), while the DOPC vesicles are not fluorescent. Frames (i-ii) in Fig. 2a show the configuration of vesicles around the bubble before the microstreaming flow is activated (pA = 0 kPa). The phase contrast image in frame (i) shows several vesicles ranging in radius from a few microns up to 25 μm. The fluoresence image in frame (ii) shows only the SOPC vesicles. When the microstreaming flow is activated, with an acoustic pressure pA = 14 kPa, the vesicles are slightly deformed as shown in frame (iii). Increasing the acoustic pressure to pA = 22 kPa causes significant deformation and rupture of the vesicles as shown in frame (iv). Frames (v-vi) show the configuration after the microstreaming flow has stopped (pA = 0 kPa). SOPC and DOPC vesicles larger than 15μm have ruptured, and only small SOPC and DOPC vesicles are present. Small vesicles can either be the product of the break-up of larger vesicles, or they were initially present and have not ruptured. These observations are consistent with the magnitudes of the capillary numbers, , and the critical capillary numbers, , for SOPC and DOPC membranes. The graph in Fig. 2a reports the capillary number, CaK = ηGmaxR/KA, as a function of KA, for two different vesicle radii, R = 15μm and R = 30μm. The other parameters are representative of typical conditions in the experiments, i.e., a characteristic stress τmax = ηGmax ≈ 100 Pa. For the experiments of Fig. 2, it is not possible to obtain τmax from Eq. (1), because the bubble oscillations are non-linear. Estimates of τmax that motivate the assumption made here are provided later in the paper. The horizontal lines represent the values of the critical capillary number, , for SOPC (dashed line) and DOPC (solid line). The critical capillary number depends only on the properties of the membrane, and not on the vesicle size or the flow conditions. For vesicles with R = 30 μm, the capillary numbers for both SOPC and DOPC vesicles exceed the respective thresholds for break-up (solid circles). For radii R = 15μm and smaller, both SOPC and DOPC vesicles exhibit capillary numbers below the respective thresholds for break-up (open circles). We observed approximately 10 SOPC vesicles and 20 DOPC vesicles, and found probabilities of break-up of vesicles larger than 15 μm in the same flow conditions of 70% and 65%, respectively. Because SOPC and DOPC vesicles present similar values of stretching elasticity, KA, and of the critical capillary number (see Table 1), selective break-up of only one population is not possible.

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical Engineering, Imperial College London, London SW7 2AZ, United Kingdom.

ABSTRACT
Vesicle 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.

No MeSH data available.


Related in: MedlinePlus