Recent reports have shown that an inkjet printer can be modified to put live cells on to a substrate [7,8]. Xu et al.  printed two different kinds of mammalian cells, an epithelial cell line [CHO (Chinese-hamster ovary) cells] and rat embryonic motoneurons, with good viability through the printing process. Survival rates beyond several days, however, appeared to be compromised, indicating potential limitations in this approach. The inkjet printing process is harsh, with very high temperatures (in excess of 300 °C) and shear force (so high it is difficult to measure), generated in the nozzle. Most cells, especially delicate ones like neurons, are likely to be compromised during this process. In addition, because the tip of the nozzle is not much bigger than a cell body (20–30 μm), cells can clog the tip.
These technical challenges may now have been overcome through the use of a modified version of the inkjet. In this issue of Biochemical Journal, Eagles et al.  demonstrate that EHDJ (electrohydrodynamic jet) printing technology can be modified to deposit droplets of living cells from a nervous-system-derived cell line. Applying a voltage of approx. 30 kV between an electrode and the print nozzle causes the contents of the nozzle to be expelled and disperse into droplets. Although the tip of the nozzle in inkjet printing is restricted in size, an EHDJ nozzle can be much larger, reducing the shear force and the chance of clogging. Two exciting findings from this paper are that: (1) CAD cells, a neuron-like cell line, can withstand the applied voltages used in electrospraying, attach to the substrate and remain viable, suggesting that neurons could withstand the printing procedure as well, and (2) 1 month after printing, at least some cells that survived the printing procedure could be induced to extend processes and take on a neuron-like phenotype. Now that living cells from a nervous-system-derived cell line have been printed on to a substrate successfully, the answers to two key questions will test the potential of this new EHDJ technique. The first question addresses the precision with which cell ejection can be controlled. For example, can cells be printed to a specific predetermined spot on a surface? The second question addresses the robustness of the method. Will neurons that have been dissociated directly from nervous system tissue withstand the EHDJ printing procedure? If fragile primary neurons can be printed accurately, then this new method will open the door to high-precision neural-circuit building.