Replacing lost limbs is a concern because there aren't any good options out there. To address the concern, researchers are turning to growing limbs in the lab, providing hope for the 185,000 amputees the United States sees every year.

The process starts with creating a bare scaffold that will be the foundation of the limb. In the lab, this is a monkey arm that has been stripped of all individual cells. Once all of the donor cells have been removed, the scaffold is infused with cells from the recipient which will grow and transform into a limb. Ultimately, the goal is get the limb back to fully function.

Current options for amputees mostly boil down to prosthetics or transplants. The problem with them is that prosthetics offer limited control and movement while transplants require the lifetime use of immunosuppressive drugs to keep the recipient's immune system from attacking the new limb. However, suppressing the immune system opens up the body for other threats like infections and certain cancers.

The research led by Harald Ott, Massachusetts General Hospital's organ repair and regeneration lab director, has an ambitious goal and that is to provide fully functioning limbs to amputees that can be transplanted as if they were their own.

"If it works out you could regenerate ... on demand," said Ott.

Ott has successfully grown organs in the lab before and has progressed to regenerating a rat arm last June. Now, his team has moved on to growing monkey limbs, using a monkey arm for the scaffold and progenitor cells from humans.

Progenitor cells are ideal for what the researchers want to achieve because they can be differentiated to develop into various cell types. They can be considered similar to stem cells except progenitor cells have a more specialized ability so it is easier for them to reproduce into specific cells.

Currently, the researchers are working with Macaque monkeys and they've so far succeeded in growing human vascular tissue and lining cells.

Maximina Yun from the University College London said Ott's team has taken a very good first step but there are challenges that still have to be overcome. She and Ott are in agreement that a limb grown must not be of any threat to humans.

Ott acknowledges that there will be difficulties ahead but he is confident that they will succeed in this lifetime.

Photo: Marieke IJsendoorn-Kuijpers | Flickr