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Research

Artificial Cells

MEMS and microTAS technologies can be powerful tools when performing high-throughput,and high sensitive analysis with extremely small amounts of solution. When confined in a small volume, chemical reactions are easily detectable by large changes in the concentration of products; thus preparing micro-sized vessels (including W/O emulsions, liposomes) by these technologies is getting important not only for single molecules and single cell analysis but also for an artificial cell assembly.

Blowing Vesicles!: A Simple Method for Direct. Microencapsulation in Lipid Vesicles

We proposed a “Blowing Vesicles” method: a preparation method of lipid vesicles inspired by forming soap bubbles from a soap film. In the method, lipid vesicles are blown out of the pre-formed bio-functional planar lipid membrane, directly encapsulating ejected materials. This method allows us to prepare uniform-sized vesicles in a short time, without post-processing. A planar lipid bilayer membrane (1×1 mm2), where membrane proteins could be reconstituted, was formed vertically by contacting two water phases surrounded by an organic solvent that contained phospholipids. A fine capillary jet nozzle was brought near the membrane, and a short pulse jet flow was created by the brief opening of the micro dispenser’s electromagnetic valve located between an air compressor and a nozzle. When the jet was applied, the membrane deformed and stretched significantly, and the neck of the stretched column was pinched off. Satellite vesicles were also generated occasionally. This process could be repeated to form a number of vesicles. The most important advantage in this method is that any materials ejected are directly encapsulated, regardless of their size, concentration, and chemical properties. As a demonstration, we encapsulated Jurkat cells and chromosomes from Hela cell cytosolic extract. While there are still many interesting aspects to be characterized in terms of the mechanism of vesicle formation, we believe the encapsulation of biological materials with this method will be a promising route to artificial cell systems. Blow vesicles!

Electroformation of giant liposomes in microfluidic channels

We present an on-chip method to produce various types of giant liposomes using electroformation in microfluidic channels. These channels were sandwiched between glass slides coated with indium tin oxide (ITO) electrodes. Giant liposomes were formed inside the channels by applying an ac voltage. Important characteristics of the obtained liposomes were investigated quantitatively. We found that 54% of the liposomes produced by electroformation had diameters exceeding 10 μm and that 90% of the liposomes did not enclose extra liposomes inside themselves. Using two microfluidic channels, we found that giant liposomes with nano/micrometre- sized materials encapsulated were formed simultaneously on a chip.

Utilization of cell-sized lipid containers for nanostructure and macromolecule handling in microfabricated devices

We propose an original approach to handle submicrometer-sized biological or inorganic materials in microfabricated devices for micro total analysis applications. Cell-sized liposomes were utilized as containers for nanoparticles, green fluorescent proteins, or DNA and handled within a microfluidic chip. Due to the micrometer size of these liposomes, their detection could be achieved by conventional optical systems. Moreover, liposomes are hardly sensitive to Brownian motion; their trapping or transportation is thereby made easy with electrostatic-based techniques, for instance, developed the past few years for cells and particles. Encapsulated materials were confined for long durations with respect to the diffusive scale time, and the liposome membrane provided excellent protection from the outside environment, inhibiting undesirable interactions. A microfluidic device consisting of a flow cell covering an array of asymmetric electrodes allowed us to convey readily liposomes by the AC electroosmosis effect. We also assessed the electrofusion of liposomes between micromachined electrodes, opening up controlled initiation of reaction inside these containers; it was exemplified by fusing differently colored liposomes. We observed that a large fraction of the liposomes fused for electric field intensity around 6 kV/cm. Applications ranging from ultrasmall biomimetic reactors to large-scale drug delivery or cell labeling can be envisaged.

A microfluidic device for electrofusion of biological vesiclesm

This paper reports a microfabricated device with high aspect-ratio electrodes and low power consumption for the electrofusion of liposomes and cells. The applications may range from gene transfection or cell tracking to biophysical studies of membrane proteins. The device consists of 250 microm thick silicon electrodes bonded to a glass substrate and covered by a PDMS-coated glass slide. Liposomes were first aligned by AC voltage at 300 kHz and then fused with short DC pulses. The fusion yield can reach 75% and is globally better for liposome diameters larger than 10 microm. The encapsulation of microbeads inside liposomes has also been demonstrated and opens up the route towards fusion-based delivery of artificial microstructures into cells.

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