22 juin 2015

Faire "pousser" un membre neuf en laboratoire

Les avancées scientifiques ne cessent de m'émerveiller. Celle-ci est particulièrement stupéfiante:

IT MIGHT look like an amputated rat forelimb, but the photo (...) is of something much more exciting: the limb has been grown in the lab from living cells. It may go down in history as the first step to creating real, biologically functional limbs for amputees.

"We're focusing on the forearm and hand to use it as a model system and proof of principle," says Harald Ott of Massachusetts General Hospital in Boston, who grew the limb. "But the techniques would apply equally to legs, arms and other extremities."

"This is science fiction coming to life," says Daniel Weiss at the University of Vermont College of Medicine in Burlington, who works on lung regeneration. "It's a very exciting development, but the challenge will be to create a functioning limb."

(...) The technique behind the rat forelimb – dubbed "decel/recel" – has previously been used to build hearts, lungs and kidneys in the lab. Simpler organs such as windpipes and voicebox tissue have been built and transplanted into people with varying levels of success, but not without controversy (...)

In the first, decel step – short for decellularisation – organs from dead donors are treated with detergents that strip off the soft tissue, leaving just the "scaffold" of the organ, built mainly from the inert protein collagen. This retains all the intricate architecture of the original organ. In the case of the rat forearm, this included the collagen structures that make up blood vessels, tendons, muscles and bones.

In the second recel step the flesh of the organ is recellularised by seeding the scaffold with the relevant cells from the recipient. The scaffold is then nourished in a bioreactor, enabling new tissue to grow and colonise the scaffold.

Because none of the donor's soft tissue remains, the new organ won't be recognised as foreign and rejected by the recipient's immune system.

(...) But would the limb's muscles work? To find out, the team used electrical pulses to activate the muscles and found that the rat's paw could clench and unclench. "It showed we could flex and extend the hand," says Ott. They also attached the biolimbs to anaesthetised healthy rats and saw that blood from the rat circulated in the new limb. However, they didn't test for muscle movement or rejection.

(...) "It's a notable step forward, and based on sound science, but there are some technical challenges that Harald's group has to tackle," says Steve Badylak of the University of Pittsburgh in Pennsylvania, who has used grafts built on scaffolds made from pig muscle to rebuild damaged leg muscles in 13 people. "Of these, the circulation is probably the biggest challenge, and making sure even the tiniest capillaries are successfully lined with endothelial cells so that they don't collapse and cause clots," he says. "But this is really an engineering approach, taking known fundamental principles of biology and applying them as an engineer would."

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