Transplantable Rat Limb Grown in the Lab

Researchers at Massachusetts General have developed an experimental technique that could be used to create complex tissues, and possibly whole bioartificial organ replacements.

Kristopher Sturgis

For a salamander or starfish, it is not big deal to lose a limb: they simply grow new ones.

Researchers at Massachusetts General Hospital in Boston are working in the lab to accomplish the same feat for other animals.

Recently, a team led by Harold Ott, MD, have reportedly created the world's first lab-grown biolimb--a rat leg that can circulate blood and respond to stimuli, according to a news release. The encouraging results indicated that the technique of growing bioartificial limbs might not only be possible, but could serve as the ideal solution for replacement limbs.

The study uses a technology that Ott discovered through his own previous research that involved living cells that are stripped from a donor organ with a detergent solution, before the remaining matrix is repopulated with progenitor cells appropriate to the specific organ. His team has used this technique to regenerate kidneys, livers, hearts, and lungs from animal model--however this was the first time they successfully engineered the more complex tissues of a bioartificial limb.

In this case, progenitor cells from the recipient rat were being grown in culture to produce muscle and vascular cells. Once the limb was stripped of its original cells, the group placed it in a nutrient solution-filled bioreactor before injecting it with the lab-grown cells. After five days in the reactor, the group applied electric stimulation to encourage muscle growth.

The limb then spent two weeks in the reactor before being removed, after which it was observed that the limb had functioning muscle cells in the muscle fibers, as well as live vascular cells in the blood vessel walls. When the muscle cells were activated through electrical stimulation, the group found them to have 80% of the strength found in a newborn rat's forelimb muscles. They also found that when the limb was transplanted onto the recipient rat, its blood vessels quickly filled with blood and became a part of the circulatory system.

Ott noted that regrowing nerves within a limb graft and reintegrating them into a recipient's nervous system remains one of the most significant challenges that lie ahead. Doing so would enable recipients to regain better motion of the replacement limb, as well as experiencing full sensation, something that the prosthetic community is still hoping to achieve with the next wave of sensing technologies that enable amputees to feel with their prosthetics.

Ott and his group, however, are hopeful this technology could provide a solution to more than just amputees in need of a limb. His team are now looking at ways of regrowing other limb tissues such as bone, cartilage, and connective tissue. The group even decellularized the forearm of a baboon, indicating that the procedure could be used on primates sooner than originally thought.

Perhaps one day this technology will eventually usurp lengthy donor lists, as we begin to replace our own faulty organs and missing limbs with lab grown replacements?