Scientists at the University of Texas have developed a new type of synthetic bone that is virtually identical to natural bone. The new material is much stronger than previous bone substitutes and better able to withstand stress, the Texas researchers said last week.
Tests have shown that once the new material is implanted in animals, it is slowly broken down by bodily processes and replaced by living bone. This stimulation of new bone growth suggests that the grafts should last indefinitely, the researchers said.
Experts predicted that the new material may prove useful in orthodontics, reconstruction of shattered bones and replacement of bones or bone fragments removed in cancer surgery.
"The potential is enormous," said biomedical chemist Alan Davison of the Massachusetts Institute of Technology. "I don't know anything that comes even close to matching it."
About 65 percent of living bone is composed of a mineral known as hydroxyapatite. This mineral provides strength and rigidity and acts as a porous matrix that supports bone marrow, bone-synthesizing cells and blood vessels. Tooth enamel is a pure, nonporous form of hydroxyapatite.
Researchers have synthesized hydroxyapatite in the past as a replacement for bone, said pediatric surgeon F. Judah Folkman of the Children's Hospital Medical Center in Boston, but the synthesized form has been very brittle and broke easily. Researchers have tried to strengthen the hydroxyapatite by reinforcing it with silica, alumina or organic polymers, but those materials increase the risk of the body's rejecting the bone substitute, he said.
Surgeons also use bones from cadavers for repairing or replacing bones, but these bones are even more likely to be rejected and are not generally available to most surgeons, according to plastic surgeon Marc Gottlieb of City of Hope Medical Center in Duarte, Calif.
"No bone graft material around now is ideal," Gottlieb said.
Chemist Richard J. Lagow and graduate student Paul J. Capano of the University of Texas have devised a technique to synthesize pure hydroxyapatite in a form that is very strong, Lagow said in a telephone interview. They can produce it in a porous form "virtually identical" to natural bone, he said, or in a denser form like that found in tooth enamel.
When they implant the porous material in animals, he said, the animal's own natural bone covers and grows into the pores over a two- to four-week period, and blood vessels grow into the pores. Over longer periods of time, the synthetic bone is broken down by specialized cells and replaced with natural bone -- just as the body's own bone is continually replaced.
"This is the only material I know of that, if you put it in the body, capillaries vasculate it, cells grow . . . and real bone replaces it," said MIT's Davison.
The material has so far had very limited tests in humans. Oral surgeon Edward T. Farris of the Baylor Medical Research Center has used it in a few patients for reconstruction of the jaw in oral surgery and has found that it worked very well, Lagow said.
J. Lester Matthews, executive director of the Baylor Medical Research Foundation and a member of Lagow's team, said he was working with several orthopedic surgeons in the Dallas area and he hoped that they would be able to implant the new material in humans soon. The surgeons will, however, first have to get approval from their local bioethics committees and from the U.S. Food and Drug Administration.
The first orthopedic uses, Lagow said, would probably be for replacing small bone fragments or segments. But, he said, they can produce the hydroxyapatite in blocks large enough to replace any bone in the body. --