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With the need for transplant organs growing, researchers are making progress toward developing them, using cultured cells and special polymers
Call it the seaweed that's changing medicine. On a balmy summer afternoon in 1986, surgeon Joseph Vacanti of Harvard Medical School in Boston was sitting on a stone breakwater near his Cape Cod vacation house watching his four children play on the beach. He and biomedical engineer Robert Langer of the Massachusetts Institute of Technology (MIT) had been trying for more than a year to devise new ways to grow thick layers of tissues in the laboratory-a first step toward their long-term goal of growing replacements for damaged tissues and organs.
But even though they were using the latest in cell-friendly, biodegradable polymers as scaffolds to support the growing tissue, the thickest slices they could grow were thinner than a dime-not much use for building complex three-dimensional organs like livers, kidneys, or hearts. The problem, Vacanti realized, was that as the tissues thickened, the interior cells couldn't take in enough nutrients and oxygen or get rid of sufficient carbon dioxide to continue growing.
Then, as Vacanti gazed into the water, inspiration struck. He spotted a seaweed waving its branches, silently soaking up nutrients from the water around it. He immediately made the connection: Branching is nature's way of maximizing surface area to supply thick tissues with nutrients, and polymer materials that branch, rather than being completely solid, would be porous enough to support growing tissue in the lab. Vacanti raced up the road to a pay phone to call Langer. "He asked if we could design [biodegradable] polymers that had a branching structure," Langer recalls. "I said, `Well, we could probably do that,' and we tried and we did."
Thirteen years later, branched biodegradable plastics and related sponge-shaped plastics undergird tissues growing in dozens of laboratories around the world. Some of the simpler of these tissues, including skin and cartilage, have already made it to the clinic or are on their way (see sidebar). But, fueled by recent advances in polymer chemistry, in the design of the bioreactors that incubate the tissues, and in the understanding of basic cell and tissue biology, researchers are also beginning to grow organs with more complex architectures.
Two...