Labs report progress in regrowing bones
Stem cells could help injured troops
By Kelly Kennedy - Staff writer
Posted : Sunday Oct 11, 2009 9:22:28 EDT
ATLANTA — As military doctors in Iraq and Afghanistan have seen more horrific injuries involving skin, nerve, vascular and bone losses from explosions, they have tried to think of what more could be done for the victims besides bandaging things up and hoping for the best.
Maybe they could regrow the tissue: Grow the cartilage, grow the blood vessels, grow the nerves and even grow the bone.
It sounds a bit like science fiction. But it has become reality — including new noses, ears and even thigh bones — sooner than anyone had hoped.
And the key is stem cells — the cells found in all multicellular organisms that can renew themselves through division and morph into a diverse range of other specialized cell types.
“If we can inject stem cells into the injured area and keep them there, they can help the tissue reform with minimal damage,” said Barbara Boyan, director of the Georgia Tech Center for Advanced Bioengineering for Soldier Survivability. “We have a regeneration capacity.”
Using grants from the Army Institute of Surgical Research and the Armed Forces Institute of Regenerative Medicine, labs at Georgia Tech have regrown nose cartilage, are working on growing much more complex ear cartilage, and have regrown femur bones in 12 weeks.
So far, all of this has been accomplished only in rats. But Boyan believes the institute is only a couple of years away from getting approval to try the new methods on humans.
For combat troops who have lost a limb, suffered severe nerve damage or have serious scarring, this could mean the difference between living the next 60 or 70 years with a disability or being able to function as they did before their injuries.
At a university lab, researchers carefully cut eight millimeters of femur bone from the thigh of a rat, leaving sections of bone at both the hip and the knee joints.
They screwed a metal brace into those end sections to hold them in place, wrapped nanofiber mesh covered with stem cells gathered from amniotic fluid in a tube between the ends of bone, and fill the mesh with protein for the cells to adhere to as they are released. Then they stitched the rats back up.
Twelve weeks later, the thigh bone grew back — as strong as it had been before researchers removed it.
“We can completely restore mechanical strength,” said Bob Guldberg, associate director of the Institute for Bioengineering and Bioscience at Georgia Tech. “It’s the first time we’ve regenerated the limb to be as strong as it was before injury.”
Until recently, researchers and doctors tended to look at each tissue group separately — they would work on healing the bone, then the vascular system, nerves and skin. But they realized they were missing out on a prime healing tool that could more tightly focus the overall healing process: stem cells.
A stem cell is a sort of “beginner cell” that has not yet assumed a specific function or form such as bone, blood or nerve. The younger a person is, the more stem cells are present; they start to diminish around age 20, when most people finish growing.
A key aspect of growth is that everything — nerves, blood vessels, bones and skin — grows together. Just as the body doesn’t put things together one at a time, researchers realized they’d do better to treat everything at once.
“Nobody has really looked at this before ... integrating the processes,” Guldberg said.
Boyan focused on facial injuries, thinking of troops with darker skin tones where scar tissue showed up vividly on the face.
About 30 percent of combat injuries are to the face. “You can’t hide a face injury,” she said.
Rats with injuries to the zyphoid cartilage in the chest — similar to that of the nose — are healing within a month.
The efforts at Georgia Tech built on the research of others, specifically Tom Clemens of Johns Hopkins University in Baltimore.
Normally, bones and blood vessels grow at the same time. Clemens found that a chemical called a hypoxia-inducible factor linked the two processes and could be stimulated to enhance repair.
Guldberg used Clemens’ drug in his femur research, which he described in the Journal of Bone and Mineral Research.
One question that needs to be answered before the research goes further is how stem cells can be kept available for combat doctors to use. The quicker an injury is treated, the more likely it is that the body will use its existing stem cells to repair itself. But combat surgeons need a way to add to those already-occurring stem cells without having to send anything out of the operating room for processing.
Boyan said it may be possible to harvest troops’ own stem cells as part of the pre-deployment process so medics have them available if necessary. Or they may be able to create a bank of stem cells from adult volunteers.
But Guldberg said the bottom line is that if the process works in humans, which he thinks it will, injured troops could grow new femur bone just as fast as the experimental rats: 12 weeks.