On-chip extrusion of lipid vesicles and tubes through microsized apertures

In this work we present the formation of micrometre-sized lipid vesicles and tubes with perfectly homogeneous diameter and extraordinary length. The method is a novel approach for unconventional fabrication of soft-matter microstructured devices based on the combination of top-down and bottom-up fabrication processes. Photolithography techniques are applied to fabricate microsized apertures that provide the requirements to form lipid structures with predictable size and to align and guide the vesicles and tubes in microstructured channels. The formation is facilitated by self-assembly of polar lipids to a lipid membrane that is afterwards forced to undergo a shape transformation by extrusion through a microsized aperture. Both the geometrical restriction by the small aperture and the pressure difference between the top and bottom sides of the aperture determine the form and length of the vesicles and tubes. A strong pressure difference favors the formation of lipid tubes, while a low pressure difference results in the formation of vesicle bunches with spherical and cylindrical shapes. Potential applications for the formed lipid structures could be as microreactors and transport channels as well as in the construction of flexible microfluidic networks.