GEORGE RETSECKA wide array of transfection techniques exist for inserting particular molecules into particular cell types, but what’s needed is a more generalized approach for getting molecules of all shapes and sizes into any type of cell, says Klavs Jensen, professor of chemical engineering at the Massachusetts Institute of Technology. So he devised a method that involves sending cells through narrow microfluidic channels that cause the cells to deform, creating tiny holes in their membranes through which molecules enter by diffusion.
Unlike transfection techniques that require chemical treatments or viral vectors, techniques that rely on physical disruption of cell membranes—such as electroporation, cell shearing, and Jensen’s cell-squeezing approach—have the advantage of being suitable for clinical use. But cell squeezing has an additional benefit, says Mark Prausnitz of the Georgia Institute of Technology, who was not involved in the work.
“The real strength of this approach is that by using a microchannel you have such exquisite control,” Prausnitz says. “You know exactly how big the channel is, you know exactly the velocity of the fluid through it, and you can control [both] perfectly.” Electroporation and cell shearing are coarser by comparison, and thus getting the balance between efficient transfection and minimal cell death is tricky.
Although the most precisely controllable technique is microinjection, in which molecules are directly injected into individual cells, “it’s so slow,” says Jensen. His cell-squeezing microchannels are capable of transfecting approximately 1 million cells in just under a minute—before the channels become clogged, he explains.
The technique is also versatile. Jensen and his team have so far transfected HeLa cells with gold nanoparticles, carbon nanotubes, antibodies to tubulin, quantum dots, plasmid DNA, siRNA, and various proteins. (PNAS, 110:2082-87, 2013)
|PHYSICAL TRANSFECTION TECHNIQUE||HOW IT WORKS||ADVANTAGES||DISADVANTAGES|
|Electroporation||Cells are subjected to electric current, causing tiny holes to form in membrane.||Well established. Electrodes placed in the body can be used to directly deliver molecules in vivo. Also used on cell suspensions||Can cause cell death. Electric current can damage molecules of interest, e.g., causes quantum dots to aggregate.|
|Cell squeezing||Cell deformation during passage through narrow microchannels causes membranes to disrupt.||Good efficiency because parameters such as channel diameters and flow speed are highly controllable||Only for use on cell suspensions|