A
team of regenerative scientists and surgeons at Massachusetts General
Hospital successfully grew a semi-functional rat forelimb in the lab,
employing a technique previously used to build bio-artificial organs.
The same technique has been used to regenerate kidneys, ears and
lungs in the lab. However, a limb is a bit trickier since it requires a
wider variety of cells than these organs.
Scientists
first used a special detergent to strip away every living cell except
the protein-based collagen that gives vessels, tendons and muscles their
shape. Then, researchers inserted muscle and vessel progenitor cells
from a different rat.
In
the future, these cells would be taken from the limb recipient, so that
the final product would be biologically compatible with his or her
body. To encourage growth, scientists placed the limb in a bioreactor
that supplies nutrients, oxygen and electrical stimulation to the
developing limb. It took about two to three weeks for it to finish
growing, after which it was ready for testing. When
scientists stimulated the forelimb with electricity, the paw clenched
and unclenched, showing that the muscles were functional. When they
attached it to anesthetized rats, blood flowed through the new limb,
though it they didn’t test it for movement
Around
the world, roughly 70 patients have undergone a hand transplant with
favorable outcomes. However, the immune system tends to reject an
unfamiliar hand, so these patients need to enroll in life-long
immunosuppressive therapy. In the new approach, the big advantage is
that the regrown cells are the recipient’s, so the risk of immune
rejection is low.
The
next challenge for scientists is to ensure nerves take root within a
bio-artificial limb, which does occur in hand transplants. It isn’t
clear if the same will occur in bio-artificial limbs.
Fig. 1: Scientists’ regrown rat limb
Fig. 2: Scientists’ rat limb grows in the bioreactor
Ref: Bernhard J. Jank et al., 2015, Biomaterials
doi:10.1016/j.biomaterials.2015.04.051
