Initial Steps Taken to Regenerating Whole Limb

The initial steps toward developing “bioartificial” replacement limbs that are appropriate for transplantation reportedly been taken by a team at Massachusetts General Hospital, who reported about their work with an animal model in the journal Biomaterials.

The investigators removed away the cellular material from the rat forelimbs, but preserved the primary vasculature and nerve matrix. Image Credit: Dr. Bernhard Jank/Ott Laboratory
The investigators removed away the cellular material from the rat forelimbs, but preserved the primary vasculature and nerve matrix. Image Credit: Dr. Bernhard Jank/Ott Laboratory

Over 1.5 million People in America have lost a limb. Prosthetic limbs have significantly advanced in function and appearance, but the authors of the new paper understand that the devices still have many restrictions.

Some sufferers over the past 2 decades have obtained hand transplants from donors, but this process comes attached with long term risks from immunosuppressive therapy.

This issue could be fixed by using the patient’s own progenitor cells to regrow the tissue for a new limb – instead of depend on a donor – but an proper matrix or scaffold has yet to be developed on which researchers would be capable to grow the new tissue.

Senior author of the research Dr. Harald Ott said, “The composite nature of our limbs makes developing a functional biological alternative particularly difficult.”

“Limbs consist of bone, nerves, blood vessels, muscles, tendons, cartilage and ligaments. Each of which has to be renewed and needs a particular supporting structure known as the matrix. We have proven that we can preserve the matrix of all of these tissues in their natural connections to one another, that we can culture the whole construct over extended periods of time, and that we can repopulate the vascular system and musculature.”

In animal models, Dr. Ott and co-workers have earlier been capable to regrow kidneys, lungs, hearts and livers using a detergent solution to remove living cells from the donor organ, which is then repopulated with proper progenitor cells.

On the other hand, the new research shows the initial use of this method to engineer a bio-artificial limb, which is more complicated.

Cellular material was removed from the limbs of deceased rats, but nerve matrix was preserved

In dead rats, the investigators removed away the cellular material from the animals’ forelimbs over the duration of 1 week, but preserved the primary vasculature and nerve matrix. This remaining material presented a structure for all of the composite tissues needed by the limb.

This forelimb matrix was then populated by cultures of muscle and vascular cells in a bio-reactor. The vascular cells were inserted into the primary artery of the limb, in an attempt to regrow veins and arteries. The progenitor cells, at the same time, were inserted into sheaths in the matrix that define muscle positions.

The limb was electrically triggered after 5 days to encourage muscle development. After 2 weeks, the limb was taken out from the bioreactor. The investigators found that the electrical stimulation triggered the new muscle fibers to contract with a strength that was 80% that of a newborn rat.

When the forelimbs were transplanted into recipient rats, blood rapidly started to flow in the new limb, and when the muscles within the graft were triggered electrically, the wrists and digital joints of the rats’ paws flexed properly.

The research team also de-cellularized baboon forearms successfully, which the authors state confirms the practicality of using the method on a scale similar to human patients.

However, the investigators still face the obstacle of reintegrating the regrown nerves of a re-generated limb into the recipient’s nervous system.

“In clinical limb transplantation, nerves do develop back into the graft, allowing both motion and sensation, and we have learned that this procedure is mostly guided by the nerve matrix within the graft,” Dr. Ott says.

Dr. Ott thinks that the same logic will apply to bioartificial grafts. Next, the team will try muscle re-growth using human cells, before broadening the procedure to human bone, cartilage and connective tissue.