Researchers at Massachusetts General Hospital (MGH) have taken the first step toward developing artificial, lab-grown limbs, building a rat forelimb with functioning vascular and muscular tissue.

This experimental approach could be applied to the limbs of primates— creating replacement limbs suitable for transplantation, a challenge because of the composite nature of limbs.

“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,” Dr. Harald Ott, of the MGH Department of Surgery and the Center for Regenerative Medicine, said in a news release Tuesday.

For the study, senior author Ott took living cells from a donor organ, stripped them with a detergent solution, then repopulated the remaining matrix with progenitor cells appropriate to the specific organ. Using this technique, researchers removed cellular materials from deceased rats and preserved the primary vasculature and nerve matrix.

The team created a cell-free matrix and injected muscle progenitors directly into the matrix sheaths that define the position of each muscle. Over two weeks later, 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, according to the press release.

When the isolated limbs were tested for functionality, muscle fibers contracted, and the wrists and digital joints of the animals’ paws flexed with electrical stimulation.

Ott, an assistant professor of surgery at Harvard Medical School, noted that the next challenge is regrowing nerves within a limb graft and reintegrating them into the recipient’s nervous system.

Researchers added that over 1.5 million Americans have lost a limb. While prosthetic technology has greatly advanced, there are still limits in function and appearance. Additionally, donor hand transplants expose recipients to the risks of life-long immunosuppressive therapy.