Scientists have taken a step closer to creating artificial human organs and using them for transplants after 3D printing produced clusters of stem cells.
In the short term, the technique could be used to generate tissue for drug-testing currently carried out on animals.
The 3D printing technology relies on an adjustable "microvalve", which builds up layers of human embryonic stem cells.
Such cells, which originate from early stage embryos, are blank slates with the potential to become any type of tissue in the body.
In the long term, the new printing technique could pave the way for those cells to be incorporated into transplant-ready laboratory-made organs and tissues, said researchers at Heriot-Watt University in Edinburgh
The technique's breakthrough is in its gentle handling of the delicate cells which gives them a greater chance to thrive, they said.
Lead scientist Dr Will Shu told Sky News: "We found that the valve-based printing is gentle enough to maintain high stem cell viability".
He also said it was "accurate enough to produce spheroids of uniform size and, most importantly, the printed human embryo stem cells maintained their pluripotency - the ability to differentiate into any other cell type".
Taking a cell from a patient and using it in the 3D printing process should enable scientists to implant the generated tissue back into the patient without triggering an immune response.
Jason King, of the stem cell biotech company Roslin Cellab, which participated in the research said: "Normally, laboratories grow cells in 2D but some cell types have been printed in 3D.
"However, up to now, human stem cell cultures have been too sensitive to manipulate in this way.
"This is a scientific development which we hope and believe will have immensely valuable long-term implications for reliable, animal-free drug-testing and, in the longer term, to provide organs for transplant on demand without the need for donation and without the problems of immune suppression and potential organ rejection."
The scientists behind the breakthrough estimate that the 3D printing technology could lead to a 'production line' of artificial organs in 10 years' time, but not before.