The machine uses a rocking motion -- 15 seesaws per minute -- to bathe the liver cells in nutrients so they can survive longer and function better. In the dog tests, Nyberg says, the cells remained fully active in the reservoir for 48 straight hours of blood detoxification. He says he's kept pig liver cells metabolically viable in the device for up to a month, and sees no reason why humans could not be kept alive while attached to the device for at least that long.

For those achievements alone, Nyberg and laboratory director Bruce Amiot deserve plaudits, says Dr. Mehmet Toner, a professor of biomedical engineering and surgery at Harvard Medical School who specializes in liver tissue preservation. "Since the oxygenization of the liver cells is a key problem in preserving them in an external device, this approach is a good step forward," he said. "Nyberg has always been very good in his controls and studies, and porcine cells are definitely better than preserved human cell lines as we now stand."

Toner explains that a few research efforts in liver-dialysis have used cryogenically preserved human cells, but those cells lose most of their liver-cleansing attributes in the freezing process. Live human cells are very hard to come by because of a lack of donors.

Another crucial aspect of Nyberg's device is that it encourages the pig liver cells to form rapidly into aggregates called spheroids. Unlike isolated liver cells, which lose functionality as they flatten out over time, spheroids of liver cells, which roughly resemble a microscopic soccer ball, perform vital liver functions at a far higher metabolic rate. "Creating a machine that can keep a very large number of liver cells alive and biochemically active is essential," Nyberg says, "because only primary hepatocytes isolated straight from a liver -- human or animal -- have been shown to perform all the necessary purification activities simultaneously."

Nyberg's machine, if it succeeds, would fill a huge technology void. Today, there are no active FDA-approved tests of any external liver device in the United States, according to the American Society for Artificial Internal Organs. Meanwhile, about 17,000 Americans are on waiting lists for liver transplants, with fewer than 5,000 livers becoming available annually. Some 40,000 Americans die every year of liver ailments.

Of course Nyberg's is not the only pig-cell device in the works. Several other corporate and academic labs are working on devices, but Toner says Nyberg's effort stands out for the length of cell life and the machine's overall capacity to cleanse blood. "There is a vital niche application for the porcine device in the sense that it keeps the patient alive while treatment is sought or while human donors become available," he adds.

Meanwhile, other researchers are trying to create genetically engineered pig livers that could be transplanted into humans, but that remains far-off and controversial.

What all researchers agree on, though, is that pig tissue is safer than tissue of other animals because humans have relatively few diseases in common with pigs.