Biophysical Society Thematic Meeting

Liposomes, Exosomes, and Virosomes: From Modeling Complex

Membrane Processes to Medical Diagnostics and Drug Delivery

Friday Speaker Abstracts

Microfluidic Methods to Study Lipid Membrane Permeation, Deformation and Fusion

Petra S. Dittrich

ETH Zurich, Zurich, Switzerland.

Microfluidics is nowadays an established technology and provides a huge toolbox for analytical

and bioanalytical methods. Microfluidic platforms facilitate precise metering and handling of

fluid volumes down to a few hundred picoliters, positioning of cells and vesicles, creating of

chemically defined liquid environments, and tailoring mechanical or physical conditions. In this

presentation, our recent microfluidic methods to study processes and properties of membranes

are introduced and discussed. For studies with vesicles, we use an array of hydrodynamic traps to

immobilize the vesicles. Each trap is positioned in a small microchamber that is defined by a

valve. The valve can be opened and closed quickly to allow for a complete fluid exchange in the

chamber. On these platforms, we investigated the passive permeation of small organic molecules

and peptides across the membranes. A modified design with larger hydrodynamic traps enabled

the immobilization of two or more vesicles and hence, studies of membrane fusion. Induced by

electrical fields or by means of fusogenic peptides, the fusion process including hemifusion

could be observed in great detail. In addition, we could gain new insights into the properties of

membranes, when exposed to mechanical forces. For these studies, we used vesicles with phase-

separated domains and deformed them while they are trapped in the microfluidic device and we

could show that lipid sorting occurs, i.e., domains fuse, upon the increase of tension.

Occasionally, we even observe budding of the liquid disordered phase. In further experiments,

we exposed the GUVs to shear stress of defined strength and were able to visualize the changes

of the domains and their relaxation after stopping the shear stress. Together, these studies may

reveal in more detail the role of the membrane in the cellular response to mechanical strains.