PROVIDENCE — In 2004, researchers at the Veterans Administration Medical Center, MIT and Brown University formed a special group with a singular purpose: build artificial arms and legs that perform like, if not someday better than, biological ones.

The need could not be greater. American troops in Iraq and Afghanistan are surviving injuries that in previous wars would have been fatal, but at the cost of damaged limbs.

Yesterday, in a crowded medical center auditorium, MIT researcher Hugh Herr — who lost both his lower legs to frostbite 25 years ago while climbing Mount Washington — walked across the stage with a new invention: the first motorized ankle-foot prosthesis.

Powered by a rechargeable battery, the robotic ankle propels users forward using sensors and tendon-like springs, relieving the hip of having to draw the leg forward as most prostheses require.

Herr compared the feeling of using the prosthesis to stepping on a moving sidewalk at an airport.

The prototype, still being improved at MIT, could become commercially available by next summer.

“We’re not sure yet of a price,” said Herr, who is 42, “but we are committed to it being affordable,” and hopefully paid for by insurance companies.

The creation of the robotic ankle is a watershed moment for this new collaborative effort, said Dr. Roy K. Aaron, a professor of orthopedic surgery at Brown. He created the Center for Restorative and Regenerative Medicine with a $7.2-million grant from the Department of Veterans Affairs.

Other researchers at Brown and MIT with expertise in fields such as tissue engineering and neuron science are carrying on other state-of-the-art work. All are working toward eventually creating true bionic prostheses — machines connected to bone and tissue which could improve mobility, reduce infections and move simply with a command from the brain, a fusion of thought and mechanics.

The center is 1 of 14 around the country where the VA partnered with college researchers to advance rehabilitation in numerous fields, including vision, hearing, wheelchair manufacturing and neuron science.

Garth Stewart, 24, of Stillwater, Minn., joined Herr on stage demonstrating a slightly more improved prosthesis than the one Herr wore. Smaller and lighter.

Stewart, a former Army infantryman, stepped on a landmine south of Baghdad in March 2003. After several surgeries, he had his left leg amputated below his knee.

The new prosthetic ankle is “leaps ahead of anything I have tried,” he said prior to walking across the stage with barely a disruption in his gait.

About 70 percent of amputees suffer back problems from imbalance and the extra work the hips must perform to move a prosthesis forward. Stewart said much of that discomfort is eliminated with the robotic ankle. “If we could get the toes to move, that would essentially seal the deal.”

Herr said several models of the prosthesis are being tested by some 20 MIT researchers who are determined to build the best synthetic ankle that mimics the natural one.

“It is a massive effort,” he said, to make the prosthesis robust enough not to break down but light enough so as not to sacrifice strength or power.

The battery, located where the calf muscle would be on a normal leg, is good for about one day of walking, or 10,000 steps.

Like a natural ankle, it has a built-in turbo system that provides more power when it senses the wearer is walking faster.

“This is a historic day,” said Sen. Jack Reed, who was among the 75 doctors, researchers, school dignitaries and others attending the news conference yesterday. “And a tremendous collaboration.”

Reed said with advances in military equipment and medicine, more troops on the frontlines are surviving attacks today while, at the same time, the number of amputations has doubled “which is why this is so encouraging.”

The device provides hope, Reed said, that soldiers can return home to productive lives.

tmooney@projo.com