A jet of air can draw out a thread of living cells and sticky polymer that could provide a way to carefully position cells to regenerate tissue or organs (Image: Suwan Jayasinghe
Currently printers use a 60-micrometre needle, so the droplets are at least 100 µm in diameter. Those needles can also damage larger cells like neonatal cardiomyocites – baby heart cells – can be 100 µm across. Squeezing them through an inkjet needle can make them rupture and die.
Jayasinghe is developing an alternative approach, called Pressure Assisted Spinning. Three needles nested inside one another separately deliver cells, a viscous polymer and pressurised air. The cells and polymer mix are drawn out and mixed by the pressurised air, explains Jayasinghe.
Vladimir Mironov of the Medical University of Southern California says Jayasinghe's simple solution doesn't tackle the problems hindering all types of cell printing. "The precise placing of different cell types [along the thread] is not possible," he says. "And [manual] cell seeding on a scaffold is laborious and expensive."
As well as inkjet printing, some researchers are experimenting with electrospinning, Mironov points out, a well-understood technology first developed about 100 years ago for making textiles.
In this process, a cell solution flows through an electrically charged hollow needle a few centimetres above an electrically grounded target. The charged solution is drawn towards the target, a little like lightning being drawn towards the Earth, pulling it into a very fine fibre with cells along its length.
But electrospinning also cannot space cells controllably, and has other drawbacks, says Jayasinghe, pointing out that up to 30,000 volts of electricity is needed. The current is low, though, making the chance of serious injury minimal. It is still a hazard, he says, one not present using pressure assisted spinning.