Material holds promise for better bone grafts


A new composite bone graft material developed at MIT holds promise for improving surgical procedures for patients who have suffered bone damage through injury or disease.

The work was headed by Dr. Cato Laurencin, an orthopedic surgeon and MIT research scientist. Co-authors of the paper presented at an August meeting of the American Chemical Society were Dr. Mohamed Attawia, a postdoctoral associate in the Harvard-MIT Division of Health Sciences and Technology, in whose lab Dr. Attawia worked, and UROP student Jessica Devin, who graduated last May. (Drs. Laurencin and Attawia moved this month to the Medical College of Pennsylvania, where Dr. Attawia is an assistant professor and Dr. Laurencin is an associate professor of orthopedic surgery and a research professor of chemical engineering at Drexel University.)

The new material consists of calcium phosphate ceramic called hydroxyapatite or HA, a material found in natural bone, and a biodegradable polymer, poly(lactide-co-glycolide) or PLAGA. This polymer is in the form of microspheres averaging 150 microns in diameter, and it acts as scaffolding for the growth of new bone in the patient. Over time, the PLAGA spheres degrade and are excreted harmlessly; the tiny holes they leave give the graft a porous structure like natural bone, allowing new bone cells to infiltrate the material. "It's something for the cells to grow on, and then it disappears," Dr. Attawia explained.

Tests using electron microscopy and other techniques have shown that the composite is "very successful" in allowing such growth, and that it also has the mechanical strength and integrity of real bone, he added.

Bone grafts now take one of two forms: autografts, in which bone is transplanted from a healthy to an injured area in the same patient, or allografts, in which bone from another person is used. Both of these methods have shortcomings, however. In the case of autografts, removing bone from one part of the body can create the same deficit there as in the area being repaired. "We're dealing with a material of limited supply," Dr. Laurencin said.

Allografts can present obstacles in the form of compatibility between donor and recipient as well as the risk of passing on diseases such as AIDS, hepatitis and others. However, treating allograft bone through freeze-drying or irradiation to lessen the chances of incompatibility and disease transmission also reduces the quality of the bone and the likelihood that it will be successfully incorporated into the patient's own bone, Dr. Laurencin said. "The need for other alternatives is there," he noted.

The number of bone graft operations-and the resulting demand for bone graft material-is rapidly increasing. In the 1970s, about 100,000 such operations were performed each year; in the 1980s, there were approximately 200,000 annually, while that number is projected to reach one million per year in this decade, he said. The surgery is indicated for patients who have suffered bone damage through a tumor or a fracture that leaves a gap in the bone. Also, patients who had hip or knee replacements many years ago and whose artificial joints have worn out are returning for repeat operations, and those procedures often require supplementary bone material, he added.

Dr. Laurencin plans to begin animal trials with the composite soon. If it proves to be effective and is approved for use in humans, it could some day be a widely used alterantive to standard bone graft materials. The work was funded by the National Science Foundation.

A version of this
article appeared in the
September 14, 1994

issue of MIT Tech Talk (Volume
39, Number
4).


Topics: Health sciences and technology

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