A rat in Boston received what scientists are calling the first lab-engineered replacement limb.

The “bio-artificial” rat forelimb is the result of a research experiment published online in the journal Biomaterials. Starting with the framework of a donor limb, scientists at Massachusetts General Hospital then brought to life using the recipient’s own cells. The newly regenerated limb is an ambitious experiment that moves the field of bioengineering closer to its goal of helping human patients.

“Once you suffer from an injury, whether it’s a burn or a heart attack or any sort of injury that leads to loss of viable tissue, your options are quite limited,” said lead researcher Dr. Harald Ott, of Mass General’s Department of Surgery and the Center for Regenerative Medicine. “Medicine has been good at making you survive. But in the end, there’s no solution or no cure for your problem.”

Using an approach that has been developed in regenerative medicine over the past several years called decellularization, Ott’s research team rebuilt and incubated a new, living rat leg structure from a deceased donor rat.

First, all donor cells were stripped with a detergent from the donor leg, leaving just the underlying structure of bones, ligaments and hollowed-out blood vessels, called the scaffolding. Then, the rat’s own stem cells were added back in to regenerate veins and arteries and jump-start the formation of muscle. Muscle cells were grown further through electrical stimulation. The whole process is documented in this time-lapse video from the lab.

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