By using a technology involving a process similar to 3D printing, Australian researchers have produced a large number of man-made tiny kidneys with stable quality, taking one step closer to the reality of bio-printed kidney for human organ transplantation.

The research, which was led by the Murdoch Children's Research Institute (MCRI) in Australia and the biotech company Organovo in the United States, was published in Nature Materials journal on Monday.

It showed how 3D bioprinting of stem cells could produce large enough sheets of kidney tissue needed for transplants.

Like squeezing toothpaste out of a tube, extrusion-based 3D bioprinting uses a "bioink" made from a stem cell paste and squeezed out through a computer-guided pipette to create artificial living tissue in a dish.

Although those bio-printed kidneys were of the size of a fingernail, they all came with a similar structure to a real kidney, including the filtering structures called nephrons, and had been used by researchers to screen drug toxicity from a class of drugs known to cause kidney damage in people.

"Drug-induced injury to the kidney is a major side effect and difficult to predict using animal studies. Bioprinting human kidneys are a practical approach to testing for toxicity before use," Professor Melissa Little from MCRI said.

With the ability to generate a large number of living kidney tissues with stable quality directly from human stem cells, Little said the technology brought the promise of tailor-made kidney treatments and eventually transplantable kidney tissue.

"The pathway to renal replacement therapy using stem cell-derived kidney tissue will need a massive increase in the number of nephron structures present in the tissue to be transplanted," she said.

"By using extrusion bioprinting, we improved the final nephron count, which will ultimately determine whether we can transplant these tissues into people," she said.