Polymer could form artificial tissue

May 31, 2002 at 12:39 PM
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CAMBRIDGE, Mass., May 31 (UPI) -- Mixing a cellular building block and an acid that normally oxidizes the body's fatty acids has yielded a "biorubber" polymer that mimics the elasticity of natural tissue until the body absorbs it, researchers at the Massachusetts Institute of Technology said Friday.

Reporting their work in the June issue of the journal Nature Biotechnology, a team lead by Robert Langer, professor of chemical and biomedical engineering at MIT, said biorubber is stable at body temperature and retains its qualities when soaked in water. The key finding is the polymer's ability to flex repeatedly and return to its original shape, Langer said.

"(In its pure form) it would be most similar to ligaments and veins," Langer told United Press International. "You can make it as elastic as you want. The easiest way is just adjusting the (chemical) ratios."

The polymer is made up of glycerol, which the body uses to create a category of fats called lipids, and sebacic acid, which helps to metabolize some fatty acids. The molecule's structure can be easily tailored to control the polymer's qualities, such as degradability and cell interaction, Langer said.

The base material is far more elastic than other biocompatible polymers, Langer said, and shows promise in animal testing. For example, pieces of the polymer implanted in rats readily incorporated living cells, the team's studies showed.

Biorubber also avoided sparking the immune system to develop fibrous capsules, a common occurrence in other implants. Its structures totally dissolved after about two months in the rats, the study showed.

George Miller, chairman of the Biomedical Engineering Program at Virginia Commonwealth University in Richmond, said Langer's team has continued its leading work in the tissue-engineering field.

"They are using very nice techniques to effectively cross-link their material with various proteins," Miller told UPI. "As a result, the final product ... is what I'll call a polymer and a biological material merged together."

The polymer has several possible applications, said Dr. Joseph P. Vacanti, head of surgical transplantation at Massachusetts General Hospital in Boston.

"Because of the physical characteristics of the material, it could act as scaffolding to help in the design of heart tissue, blood vessels, cartilage, bone and many other structures of the human body, including whole organs for transplantation," Vacanti said.

The material also could deliver medicine in time-released fashion as it degrades, Langer said, or be incorporated into existing artificial organs. "One of the things we've worked on is heart valves and things like that, so I think that's all (a fair statement)," he said.

VCU's Miller cautioned that although the polymer has several promising qualities, the true test for uses such as tissue scaffolding will be in how well all types of cells merge with the material. For example, biorubber seems elastic enough to temporarily take the place of an artery, but it would have to provide the right sort of base to combine collagen, elastin and smooth muscle cells to recreate an artery wall, he said.

Biorubber will have to undergo the rigorous U.S. Food and Drug Administration approval process, but Langer said the path should be fairly smooth.

"Both glycerol and sebacic acid have been approved in other things," Langer said. "We've also done a lot of tests with animals, and it's better than existing FDA-approved materials in those studies."

The FDA is not going to go easy on the polymer, however, no matter how its components have performed, Miller said. The combination of glycerol and sebacic acid will surely interact differently with the human body than with chemicals alone, he said, so the agency probably will want a full slate of tests.

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