Microfluidics compresses cells to gain entry

Large polysaccharides, nanoparticles, and plasmids can be delivered into a living cell using a newly discovered phenomenon in microfluidic systems, according to US researchers. The phenomenon - transient cell volume exchange using microfluidics - allows the cell's volume to be rapidly and repeatedly changed allowing the macromolecules to enter through convective intracellular delivery. [Sulchek, T. et al. Mater Today (2018); DOI: 10.1016/j.mattod.2018.03.002]

Until now, manipulation of cells with micropipettes, microcantilevers, and microfluidic devices has shown that their shape can be changed substantially, but not their volume. The new phenomenon turns this concept on its head revealing that cell volume can be manipulated for high-throughput applications. The work carried out at the Georgia Institute of Technology in Atlanta, USA, shows that 2000 kilodalton polysaccharides, 100-nanometer particles and circular strands of DNA, plasmids, can be uploaded to a cell through such manipulations. Volume change is up to 30 percent on a ten microsecond timescale and this is wholly adequate to allow the various entities to enter the cells.

The team obtained the necessary fast deformations by passing cells rapidly through a microfluidic constriction that had an abrupt, stepwise compression profile. They used high-resolution video microscopy and quantitative florescent marker delivery to monitor the changes and progress. Tests showed that despite such large volume changes that the cells remained viable and there were no detrimental effects. The approach opens up a new delivery method that was previously too inefficient to be tenable for such large entities because earlier delivery methods relied on diffusion for transmembrane transfer of molecules. The team suggests that their work could lead to a new approach to cell engineering.

The team explains this new phenomenon as occurring through a process not unlike a droplet spattering on the surface of a liquid. The microfluidic ridges create a sudden inertial compression on the cell as is passes each ridge, this vertical impact disrupts the cell membrane allowing fluid out and reducing volume briefly, then as it passes the constriction it can expand again, allowing fluid to re-enter carrying the nanoparticles and other entities with it.

This microfluidic approach, which the team calls cell volume exchange for convective transfer (cell VECT), avoids many of the drawbacks of using chemical, viral, or electrical processing to get relatively large molecules and particles into the interior of a cell. "The simplicity of use and successful delivery of an array of biologically relevant macromolecules to various cell types demonstrated great potential for a wide range of highly valuable biomedical applications," the team concludes.

"For the next step, we'd like to learn more about the mechanism, i.e. what changes are induced into cells upon fast compressions, and discover what types of cells exhibit the observed volume-change mechanism," Todd Sulchek told us. "We're interested in applying the mechanism to solve important biomedical challenges, for example lowering the cost and improving the ease of cell engineering."

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase. His popular science book Deceived Wisdom is now available.