Just 15 years ago, Bob Langer and his colleague Joseph Vacanti pioneered a remarkable new process- growing human tissues in the lab. Back in 1987, Langer and Vacanti couldn't get their work published; journal editors didn't see any practical applications. Today, the pair are acknowledged as the fathers of the field of tissue engineering. Now, Langer, Vacanti and his brother Charles, as well as teams of researchers around the world, pursue the day when replacement tissues and organs are readily available, custom-made for those who need them.
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REPLACEMENT PARTS

Today, tissue engineered skin, the first so-called "neo-organ" approved by the U.S. Food and Drug Administration, comes to the aid of burn victims and patients with severe skin sores or ulcers. In the not-too-distant future, lab-grown cartilage and bone could relieve arthritis sufferers, while blood vessels, cardiac valves and muscle tissue could save thousands of cardiovascular disease patients. Ultimately, custom-made hearts, livers, breasts, corneas, kidneys, bone marrow and bladders could offer elegant solutions to most life-threatening illnesses.

"We can't say what the timeline will be," says Dr. Joseph Vacanti, Director of the Tissue Engineering and Organ Fabrication Laboratory at Massachusetts General Hospital in Boston. "But there are thirty plus tissues we're experimenting on in our lab."

Imitating Life

This human heart valve was grown in the lab.

Cultivating tissues in the lab requires closely mimicking the environment in which cells naturally grow. This turns out to be a tall order. Unlocking the biochemical signals that influence growth and development was the first step on the road to tissue engineering. By adding the right combination of compounds, scientists coax cells into growing and proliferating.

But, to produce biologically useful tissues like cartilage and heart valves, tissue engineers must also pay special attention to the physical environment in which cells grow.

In nature, the circulatory system gives each individual cell in a tissue access to nutrients and a means of waste removal. Many of the advances in tissue engineering have been means of replicating this scenario in the lab. One of Langer's major contributions to his filed was his work in biodegradable materials that can serve as scaffolding on which cells can be seeded. Joseph Vacanti deserves credit for the idea of the scaffold itself.

"The scaffold looks like strands of spaghetti attached together," according to Langer. "The cells are seeded 2 to 3 millimeters apart and the whole apparatus is bathed in a nutritive media."

After this human ear is removed, the mouse will remain healthy.

The biodegradable scaffolding provides each cell with better access to nutrients and waste removal. Additionally, since the scaffolding can be molded into any shape or size, the tissue can be custom grown for the intended recipient. For example, to grow an ear like the one on the mouse pictured here, tissue engineers mold the biodegradable scaffold into the proper size and shape. Researchers then "seed" the scaffold with young cartilage cells and surgically implant the mold under the skin. The mouse, hairless and specially bred to lack an immune system that might reject the human tissue, nourishes the ear as the cartilage cells grow.

In the future, bits of scaffolding seeded with young cells could be implanted into ailing organs, where the body's own biochemistry would direct the young cells to grow into a "patch" of healthy tissues.

"Both functions are important," according to Joseph Vacanti. "but, in many circumstances, the shape is less important than the exchange of nutrients. "

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Photos: Charles Vacanti, MD; Advanced Tissue Sciences
Video: Advanced Tissue Sciences