Scientists have taken what may be a key step toward creating human organs such as livers and kidneys. Taking their cue from the body's own vascular system, researchers from M.I.T. and Harvard Medical School constructed a microscopic device capable of supplying oxygen and nutrients to organ cells.

Recent efforts to grow new organs have met with limited success. Whereas researchers have managed to make skin and cartilage, functional vital organs have eluded them. The problem, explains M.I.T.'s Mohammad Kaazempur-Mofrad, is that although conventional tissue engineering methods provide a scaffold for the cells of the tissue, they do not offer the vascular support necessary to nourish organs such as livers and kidneys.

To address that problem, Kaazempur-Mofrad and his colleagues used fractal computational models to design networks mimicking the intricate branching pattern of actual blood vessels. They then etched those nano networks onto silicon surfaces, which in turn served as molds for biocompatible polymer films. The next step was to sandwich a microporous membrane between two films and seal them together.

"Our microfabricated devices can efficiently supply oxygen and nutrients to sustain the viability of human liver and kidney cells for at least one week in the lab," Kaazempur-Mofrad reported yesterday at the American Society for Microbiology's conference on Bio- Micro- Nano-systems in New York City. In experiments, 96 percent of kidney cells incorporated into the artificial vascular network lived for one week; 95 percent of liver cells survived for two weeks. A liver system implanted into rats lasted a week.

So far, the team has experimented with only single-layer devices, as opposed to the 30 to 50 layers researchers believe are required to represent an operational liver. "But the ultimate goal," Kaazempur-Mofrad remarks, "is to make whole, functional organs."