Magnets Used Successfully
To Regenerate Cartilage

By Jonathan Beard
From New Scientist

Damaged cartilage in joints can be regenerated by pulling cells into the affected area with a magnet, says an orthopaedic surgeon in Michigan. Alan Halpern, a surgeon in private practice in Kalamazoo, believes that his technique could provide a cheaper, less invasive way of repairing cartilage, the tough resilient tissue that buffers the bones in joints.
"We have long been able to remove chondrocytes--individual cartilage cells--from a patient, and grow them in culture," says Halpern. But the problem is getting them back into the damaged area and keeping them there, he says.
What Halpern does is drill into the bone and insert small biodegradable magnets made of the same material as soluble sutures. The material has been seeded with particles of iron. He then tags cultured chondrocytes with 200-nanometre particles of magnetite, a strongly magnetic form of iron oxide. "When these magnetically tagged chondrocytes are injected into the joint, they migrate to the magnets implanted in the bone, so they are in the right place to form new tissue," he says.
He has successfully tested the technique in rabbits. "Cartilage from the rabbits treated with the tagged cells looked like normal cartilage. It was not as rich in cells as the original tissue, but it had the same shape and appeared functional," says Halpern. "The joints in the controls, in which magnets were implanted but no cells injected, had fibrous tissue which we know is not durable."
One of the latest methods of replacing cartilage, introduced in 1995, involves opening up the joint, sewing on some tissue taken from the leg and injecting cultured cartilage cells beneath this membrane. The membrane keeps the cells in place. The average cost of such an operation is $26 000.
Halpern, who has used this method successfully, says his technique has the advantage that the joint does not have to be opened up, because the magnets can be inserted using keyhole surgery.
He says that the new technique will also be a lot cheaper because producing the magnets and tagged cells will cost only a few hundred dollars. Halpern's company, Biomagnetics, will finance further research and clinical trials.
Daniel Grande, a medical researcher at North Shore University Hospital in New York who is familiar with Halpern's work, says it could be important. "Using magnets is attractive in theory," says Grande, "but more work will be needed to find over what distance they can attract tagged cells, and whether implanted magnets have any adverse effects."

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