The dream of regrowing limbs? It’s just gotten one step closer. Researchers at Massachusetts General Hospital have grow a rat forearm out of living cells in the lab. A primate limb may be next.

As New Scientist explains, the lab-grown limb makes use of an existing technique called “decel/recel,” short for decellularization and recellularization. It’s been used to successfully grow organs like hearts and lungs and also windpipes.

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Basically, scientists took the limb of a dead rat and doused it with detergents that got rid of all its cells. Decellularization leaves only a scaffold of collagen proteins that give blood vessels, bones, and muscles their shape.

Without any living cells remaining from the donor, the recipient’s immune system is less likely to reject it. Then comes the more difficult challenge of regrowing all those cells from scratch. Harald Ott’s lab at Massachusetts General Hospital used the following procedure, as described by New Scientist:

A forearm is much more difficult to create in this way than a windpipe, say, as a number of different cell types need to be grown. Ott began by suspending the decellularised forelimb in a bioreactor, plumbing the collagen artery into an artificial circulatory system to provide nutrients, oxygen and electrical stimulation to the limb. He then injected human endothelial cells into the collagen structures of blood vessels to recolonise the surfaces of blood vessels. This was important, he says, because it made the vessels more robust and prevented them from rupturing as fluids circulated.

Next, he injected a mixture of cells from mice that included myoblasts, the cells that grow into muscle, in the cavities of the scaffold normally occupied by muscle. In two to three weeks, the blood vessels and muscles had been rebuilt. Ott finished off the limb by coating the forelimbs with skin grafts

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The resulting limb could flex and unflex when electrically stimulated. When transplanted onto anesthetized rat, blood flowed through the limb. However, they have not yet tested whether the rat can move its limb. The team hopes that the recipient rat’s nervous system will grow into the new limb.

The researchers have also decellularized a primate arm, though it’ll be even more difficult to successfully recellularize a larger and more complex limb. Regrowing human limbs is still a long way off. But here we have is a possible path forward.

[New Scientist, Biomaterials]

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