NEW YORK (CNN) -- Scientists said Friday they had managed to grow artificial bladders for transplant into dogs, and said the technology might eventually work for people with bladder disease.

Internationally, about 400 million people worldwide suffer from bladder disease, scientists said. Patients with the worst cases often need bladder transplants, or at least serious repair to their bladders.

Human bladders can be ravaged by cancer, birth defects, nerve damage or trauma. They can be repaired or replaced with intestinal or stomach tissue, but that can lead to infection and bladder stones.

Dr. Anthony Atala of Harvard Medical School and his colleagues report in the February issue of the journal Nature Biotechnology that they grew bladders from cells which functioned normally after they were transplanted into dogs.

"It takes four weeks for the cells to grow and once you have that you can start the process of placing them onto the bladder mold," Atala, a surgeon specializing in urology, said.

"It's like layering a cake -- you basically place one layer of cells over the mold and then place it back into an incubator," he said. The incubator has the same conditions as the body.

The artificial bladders worked well for nearly a year in dogs, the scientists reported.

The researchers took small bits of bladder tissue from six dogs and grew the cells into artificial bladders in the lab. Then they put the artificial organs back into the animals, whose own bladders had been removed.

While scientists have studied artificial bladders before, "this is the best one I've ever seen," commented Dr. Eli A. Friedman, editor of the journal of the American Society for Artificial Internal Organs.

The work must be confirmed by other groups, but Atala's results provide strong evidence that the technique works, said Friedman, a professor of medicine at the State University of New York at Brooklyn.

Atala said more research is needed before the technique could be tried in people.

The technology might work for other organs, Atala said -- which would be a boon in the United States, where waiting lists for organs stretch out for years.

The U.S. Health and Human Services Department estimates that 4,000 people die every year waiting for an organ transplant.

The Associated Press and Reuters contributed to this report.