An artificial pancreas that has been tested successfully on animals may one day rescue millions of diabetics from the daily routine of insulin injections, researchers say in a study published Friday.

The plastic device, shaped like a hockey puck but slightly smaller, contains living pancreas cells that are able to respond naturally to the body's need for insulin.A membrane protects the cells from rejection by the immune system while allowing insulin to flow into the bloodstream.

The journal Science published a report Friday on the manufactured pancreas.

Dr. William L. Chick of BioHybrid Technologies Inc. of Shrewsbury, Mass., a co-developer of the device, said the invention has kept diabetic dogs healthy for months in laboratory tests. He said plans call for human clinical trials to start in about two years.

"It's a giant first step toward what is essentially a permanent pancreas transplant without the need for immune suppression drugs," said Dr. Richard Kahn, the chief scientist for the American Diabetes Association.

"It's exciting research that holds a great promise. But there's a lot of work that needs to be done yet before it can be applied in humans."

Chick, in a telephone interview Thursday, said the heart of the device is the membrane, a plastic material that he said is "selectively permeable."

The membrane lines a hollow coil inside the artificial pancreas. On one side of the membrane, insulin-producing cells, called islets, are implanted. Blood from the body circulates through the coil on the other side of the membrane.

Chick said the membrane allows small molecules from the blood to pass through and nourish the islet cells. The islets, in turn, produce insulin that penetrates the membrane to join the blood.