Boning up on biodegradable implants.

Boning up on biodegradable implants

Though the body can replace bone lost to disease and injury, it often needs help. At the Army Institute of Dental Research in Washington, D.C., researchers are tailoring biodegradable polymer microcapsules to slowly release proteins that naturally induce bone growth. They are also developing a related family of nontoxic polymers to serve as biodegradable scaffolds for bridging large gaps in damaged bone. The drug-filled beads, used in conjunction with sheets, rods, plates or tubes of the scaffolding material, appear to help guide the natural rebuilding of bone, especially in the face and skull, reports Army analytical chemist Carla P. Desilets.

Her team seeks to develop a range of products that reconstructive surgeons can custom-shape to a wound using simple dental tools, then anchor in place with biodegradable screws or glue. For thin facial bones, such as thoe around the cheeks, the researchers embed the bone-growth-promoting proteins right into the scaffolding material. Tubes filled with the microencapsulated drugs span the gaps in thicker bones, serving as rigid spacers between adjacent bone stumps. As bone precursor cells migrate to each type of implant, they incubate in its time-released growth protein and transform into solid bone. During the months it takes for the new bone to develop, the synthetic scaffolding becomes porous, eventually falling apart.

Desilets says her group is focusing on polylactic and polyglycolic acids as scaffolding materials because these polymers have a 30-year history of sale use as biodegradable sutures. In animal tests, the Army researchers have found that bone regrowth spurred by prototype implants is as strong as the original and follows the former bone's contours. Similar tests in humans could begin in as little as three to five years, she adds.

At the Massachusetts Institute of Technology in Cambridge, researchers are focusing on polyanhydrides, a newer class of biodegradable plastics, for a range of bony appliations. The first commercial application of these implants--one of which is now undergoing animal testig--may be for the slow, localized release of antibiotics to fight osteomyelitis, or bone infection, says MIT's Cato T. Laurencin. Osteomyelitis resists conventional treatment in some 10 to 15 percent of cases and occasionally requires amputation, he notes.

Biodegradable plastics may one day coat conventional joint prostheses, Laurencin adds. By seeding the slowly eroding coat with drugs, surgeons could combat the body's attempts to reject the implant while also speeding attachments between the prosthesis and adjacent bone, he says.