Scientists in America have come one step coser to the dream of growing human organs in a lab by successfully engineering a working rat kidney.
Researchers at Massachusetts General Hospital took the kidney then successfully transplanted it back into a rat's body. It also produced urine - although it only worked at 5% efficiency.
The remarkable achievement could have huge implications for medicine. Of those people on organ waiting lists 90% are waiting for kidneys.
The new research open up the possibility that instead of waiting for a donor to become available patients could essentially grow their own.
Not only would this be quicker but it would also do away with the need to take immune-suppressing drugs to treat possible rejection.
To grow the organ it first had to be "cleaned" of all its old cells using a detergent.
What remained after was a biological scaffold consisting of the kidney's blood vessels and the tubes which produce and drain the urine.
This was then coated with new cells and placed in warm environment designed to replicate the innards of a rat.
Twelve days later and researchers had a functioning kidney.
When tested on its own it was 23% as effective as a normal organ. This fell to 5% when placed inside a rat. Although this sounds low, kidney dialysis treatment typically works at around 10-15%.
Where the challenge lies is in scaling up the work to a human-sized kidney. Windpipes and bladders have already been successfully grown in a lab but these a simpler structures than kidneys.