Bone, Grow Thyself

25 July 2005 (All day)

Good As New. New bone (labeled "bioreactor") grows alongside established bone in the tibia of a rabbit.

Tissue engineers have long dreamed of growing new organs in a Petri dish and transplanting them successfully into patients. Now, researchers have moved one step closer to making that dream a reality by growing new bone inside rabbits and using it to treat bone defects in the same animal.

Attempts to grow complex tissues outside the body have progressed in fits and starts. Italian researchers, for example, have coaxed bone marrow cells in a ceramic matrix into creating new bone. But when transplanted back into the body, organisms have been unable to resorb and remodel the tissue, as occurs with normal bone. To avoid such problems, researchers led by tissue engineers Prasad Shastri at Vanderbilt University in Nashville, Tennessee, and Molly Stevens and Robert Langer at the Massachusetts Institute of Technology in Cambridge decided to see if they could let body handle it itself.

Bones in the body are sheathed in a thin membrane of cells called the periosteum. If a small wound or fracture occurs, cells in the periosteum can divide and differentiate into replacement tissue, including new bone, cartilage, and ligaments. Shastri wanted to see if he and his colleagues could use this same wound healing response to generate new tissue.

Using white rabbits, the researchers injected a surgical saline solution between the long, lower leg bone and the periosteum. This created a small, fluid-filled cavity alongside the leg bone, into which they hoped new bone would grow. To prevent the cavity from collapsing, the researchers injected a gel containing a calcium-rich compound called alginate. Previous studies have suggested that calcium also helps trigger cells in the periosteum to differentiate into new bone, and that is exactly what happened. Within a few weeks, the alginate cavities were filled with new bone. And when that bone was removed and transplanted to damaged bone sites within the same animals, the new bone integrated seamlessly, the researchers report online this week in the Proceedings of the National Academy of Sciences.

"I think the strength of this approach is its simplicity," says Antonios Mikos, a tissue engineering specialist at Rice University in Houston, Texas. That could make it a boon to orthopedic surgeons who often need to harvest large amounts of bone from patients to repair serious trauma or to fuse vertebrae in spinal fusions. Harvested bone usually comes from a patient's hip bones, a procedure that often produces pain for years. But if this approach works in people, says Mikos, it could enable physicians to generate new bone alongside a patient's shin, for example, which could then be transplanted to other sites. "I think it will have an enormous impact on the field," he says.

Related site:
Langer's Web site

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