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takyon writes:

Scientists have created rat forelimbs with "functioning vascular and muscle tissue" using techniques previously used to create bioartificial organs:

The composite nature of our limbs makes building a functional biological replacement particularly challenging," explains Harald Ott, MD, of the MGH Department of Surgery and the Center for Regenerative Medicine, senior author of the paper. "Limbs contain muscles, bone, cartilage, blood vessels, tendons, ligaments and nerves – each of which has to be rebuilt and requires a specific supporting structure called the matrix. We have shown that we can maintain the matrix of all of these tissues in their natural relationships to each other, that we can culture the entire construct over prolonged periods of time, and that we can repopulate the vascular system and musculature."

The current study uses technology Ott discovered as a research fellow at the University of Minnesota, in which living cells are stripped from a donor organ with a detergent solution and the remaining matrix is then repopulated with progenitor cells appropriate to the specific organ. His team and others at MGH and elsewhere have used this decellularization technique to regenerate kidneys, livers, hearts and lungs from animal models, but this is the first reported use to engineer the more complex tissues of a bioartificial limb.

The research team then cultured the forelimb matrix in a bioreactor, within which vascular cells were injected into the limb's main artery to regenerate veins and arteries. Muscle progenitors were injected directly into the matrix sheaths that define the position of each muscle. After five days in culture, electrical stimulation was applied to the potential limb graft to further promote muscle formation, and after two weeks, the grafts were removed from the bioreactor. Analysis of the bioartificial limbs confirmed the presence of vascular cells along blood vessel walls and muscle cells aligned into appropriate fibers throughout the muscle matrix.

[...] The research team also successfully decellularized baboon forearms to confirm the feasibility of using this approach on the scale that would be required for human patients.