"This is the first example of a non-electric field-driven jetting technique," say the inventors of the new method, scientists Sumathy Arumuganathar and Suwan Jayasinghe of University College London, who worked with medical researchers Jean McEwan and Scott Irvine of The Royal Free and University College London Medical School.

"This unique cell jetting by imposed aerodynamic forces has now joined the biological-jetting race," said the authors in the study published in a new Institute of Physics journal called Biomedical Materials.

Since circa 2001, the turn of the century, a "biological jetting race" has been ongoing, according to the authors. It began when electrical engineers (EEs) started loading ink-jet printer cartridges with living cells in suspension, from which they spewed flat, two-dimensional living structures. Since then, EEs have collaborated with biologists worldwide to "bridge engineering with biology" for the "processing, handling and fabrication of living organisms," according to the scientists at University College London.

As a result, several new jet-based techniques have been invented to directly engineer three-dimensional living organs, rather than engineering only flat two-dimensional tissues: first, by means of layering ink-jet prints; second, by using laser-directed cell writing; third, by using bio-electrospraying; and fourth, and most recently, by using cell electrospinning techniques.

All these techniques, however, have one thing in common with the simple ink-jet printing: the use of electric fields to control nozzles. The ink-jet approach produced droplets with piezoelectric-driven nozzles that are typically tens of microns in size. Using ink-jet nozzles thus proved the concept of "printing" tissues, yet bioengineers have since superseded ink-jet methods with electrosprays that can generate cell-bearing droplets in the 10 nanometer range. Electrospinning techniques have further improved the spraying approach by applying an external electric field to draw out micro- to nano-sized threads from the nozzles, thereby enabling three-dimensional scaffolds to be constructed.

The new technique invented at University College London claims to have all the advantages of past bio-jetting techniques accompanied by much more flexible results, because the cells do not have to be subjected to an electrical field to direct their assembly. Instead, a pressure difference is applied over the nozzle within a chamber. As a cellular suspension sprays out of the exit nozzle, a differential pressure between the chamber and the surroundings results in a drawing out of the flow, sans electric fields. The scientists demonstrated how the technique can direct jet nozzles to form scaffolding that ranges in diameter from a few micrometers down to only nanometers in diameter.

So far, the scientists have successfully proved the concept of aerodynamic bio-jetting on suspensions of rabbit cells, which they used to produce two-dimensional tissues. Currently they are optimizing the jetting process in preparation for engineering a three-dimensional plotter-like device that can construct the tissues needed for complete organs.