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Scientists Make Their Bones in the Lab

Growing artificial bone takes another step forward, says new research

THURSDAY, Nov. 22, 2001 (HealthDayNews) -- Scientists say they've created a self-assembling scaffold with key properties of the natural skeleton that one day could help repair not only broken or diseased bone, but other tissues and organs, too.

The findings, reported this week in the journal Science, also will be presented in Boston later this month at a meeting of materials scientists.

Many research groups are working on ways to grow synthetic bone, but they often run into trouble getting the materials to behave structurally. The reason: Bone consists of two main and structurally distinct layers.

Its platform is collagen, a protein found throughout the body that gives tissue strength. Atop collagen grow the crystals known as bone mineral, which is continually being created and destroyed by other bone cells.

While growing bone mineral on a surface such as collagen is not too tricky, coaxing it to grow on a synthetic bed has proven much more challenging.

In the latest work, Jeffrey Hartgerink, a bioengineer at Northwestern University, in Evanston, Ill., and his colleagues created tiny molecules, called nanofibers, just 8 millionths of an inch in diameter, or 10,000 times narrower than a human hair.

The nanofibers are composed of peptide-amphiphile, pieces of protein that look like a baton of cotton candy. Its fat, water-loving end is attached to a thinner segment that loathes the liquid. When placed in an acidic solution with varying salt concentrations, the fibers arrange themselves in long tubes that resemble the structure of bone collagen.

In large quantities, the material behaves like a gel that shows a liking not only for natural bone but, with a little tinkering to change its chemical properties, other cells, too.

"We still don't know anything about the mechanical properties of the nanofibers," says Samuel Stupp, a Northwestern materials scientist and a co-author of the study. "However, based on electron microscopy of the nanofibers, it appears as though fibers of varying flexibilities can be prepared, depending on the chemical structure of the self assembling molecules we start with. Also, since we demonstrated that we can internally cross-link individual nanofibers by forming covalent bonds [making chains called polymers] among the self-assembling molecules, we speculate that their strength will be high."

Adele Boskey, a biochemist who studies bone at Cornell's Weill Medical College, says the Illinois work is the closest effort yet at mimicking real bone in the lab. "We're all trying to make some sort of a bone substitute. This material does make something that is bone-like, but I underline the bone-like," says Boskey, director of research at the Hospital for Special Surgery in New York City.

The Illinois fibers are much more aligned under a microscope than natural bone tissue, which might make it more brittle, Boskey says. But without additional testing, that's not certain.

Boskey says she can envision using the substance as a platform for the body to deposit its own bone minerals, say, to help a break or bone defect heal. And it may also work well at repairing dentin, the calcium-rich area that surrounds the pulp of teeth.

Stupp says his group hopes to "chemically customize" the fibers so they'll be receptive platforms for a variety of tissues beyond bone alone. "For example, we can create nanofibers that could specifically target neurons for nerve regeneration, or pancreatic cells for new approaches in the treatment of diabetes," Stupp says.

What To Do

You don't have to wait for synthetic materials to improve your bone strength. Eating plenty of calcium and regular exercise can help build the skeleton and reduce the risk of fractures.

To learn more about bone diseases, try the National Institutes of Health.

For more on osteoporosis, a bone disease that affects 10 million Americans, try the National Osteoporosis Foundation.

And here are some facts about bones.

SOURCES: Interviews with Samuel Stupp, Ph.D., professor of materials science, chemistry and medicine, Northwestern University, Evanston, Ill.; Adele Boskey, Ph.D., professor of biochemistry and cell and molecular biology, Weill Medical College of Cornell University, and director of research, Hospital for Special Surgery, New York City; Nov. 23, 2001, Science
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