3D printers might grab a lot of headlines these days, but it was a more conventional inkjet printing setup that Cambridge University scientists used to work some medical marvels recently: For the first time, they managed to successfully print new cells onto cells extracted from rat eyes. The technology could pave the way toward ready-made artificial tissue grafts that could be used to treat various conditions that can lead to blindness.

“The loss of nerve cells in the retina is a feature of many blinding eye diseases,” Cambridge researcher Barbara Lorber and colleagues said in a statement. “The retina is an exquisitely organized structure where the precise arrangement of cells in relation to one another is critical for effective visual function.”

As described in a proof-of-concept paper published in the journal Biofabrication on Tuesday, Lorber and her team extracted two kinds of cells from the retinas of adult rats: ganglion cells, which transmit visual information from the light-sensing cells of the retina, and glial cells, which provide something like architectural support and protection for neurons. Then, they used a setup called a “piezoelectric” inkjet printer device to print onto the cells. What’s especially exciting about the find is that the cells stayed intact, and were able to grow and thrive after being printed.

Piezoelectric technology (meaning “pressure from electricity”) is used in a range of commercial printers. Unlike other kinds of inkjet printers that use heat to expand the ink so it is forced on to the paper, piezoelectric printers use components that change shape when charged with electricity. This generates pressure that forces ink out through a nozzle. Though piezoelectric printers are a little more costly at first, many companies prefer them because they require less maintenance and are less susceptible to ink clogging.

Printing with cells provides some unique challenges. Just printing with ink is a delicate balance of physics: the viscosity and surface tension of the ink have to be balanced just so. Now there’s the added difficulty of introducing delicate little cells into the mix.

Other scientists have worried that vibrations from piezoelectric print heads could burst the delicate membranes encircling cells -- hence, most cell printing to date has been done with thermal inkjet technology. But the Cambridge scientists say that the piezoelectric technology posed no problems.

“Although the cells are subjected to very high shear rates and acceleration during jetting, no significant distortion of the cell structures has been observed either immediately before or after cell ejection,” the authors wrote. “The observations suggest that either the cell membranes possess sufficient strength and elasticity to resist a brief period of high stress, or the geometry of the print head nozzle used results in rather little shear or deformation of the cells during jetting.”

It might be possible to use an inkjet cell-printing technique to make 3-dimensional structures. Most commercial and do-it-yourself 3D printers use a different kind of technique called fused deposition modeling, which heats a plastic or metal filament and deposits the material in layers. But inkjet-like systems can be used in 3D printing (also known as additive manufacturing); one printer developed at the Massachusetts Institute of Technology uses an inkjet printing head to add a binding material to a layer of plaster powder.

“We plan to extend this study to print other cells of the retina and to investigate if light-sensitive photoreceptors can be successfully printed using inkjet technology. In addition, we would like to further develop our printing process to be suitable for commercial, multi-nozzle print heads,” coauthor Keith Martin said in a statement.

SOURCE: Lorber et al. “Adult rat retinal ganglion cells and glia can be printed by piezoelectric inkjet printing.” Biofabrication published online 17 December 2013.

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