A tiny weight-loss device developed by UW-Madison researchers could someday be implanted on people’s stomachs to trick their brains into thinking they’re full.

Lab rats implanted with the device lost about a third of their body weight during testing, Xudong Wang, a professor of materials science and engineering, reported last month in the journal Nature Communications.

The battery-free device, a third the size of a penny, can generate electric pulses from the stomach’s natural churning motions, Wang said. The pulses are delivered by wires to the vagus nerve, which links the stomach and the brain.

“It will stimulate the vagus nerve to tell the brain the stomach is full,” Wang said in an interview. “It can reduce the amount of food intake and achieve the purpose of reducing weight.”

In one test, adult lab rats implanted with the device lost about 30 percent of their weight, while a control group retained their normal weight.

In another test, the weight of young rats implanted with the device increased about 38 percent less than that of other young rats, while both groups were growing into adults.

After the device was removed from the rats, their eating patterns, weight and growth rates returned to normal.

Wang and his UW-Madison collaborators, including graduate student Guang Yao and radiology professor Weibo Cai, patented the device through the Wisconsin Alumni Research Foundation.

Further tests are planned in pigs, hopefully beginning this year, Wang said. If the results are promising, the researchers plan to move to human trials, a step that likely wouldn’t happen for several years.

More than 93 million U.S. adults, or nearly 40 percent of the population, were obese in 2015-16, putting them at higher risk of heart disease, stroke, diabetes and certain types of cancer, according to the Centers for Disease Control and Prevention.

Among children, nearly 14 million, or 18.5 percent, are obese, the CDC said.

Another weight-loss device that stimulates the vagus nerve was approved by the Food and Drug Administration in 2015. It is similar to a pacemaker, delivering electrical pulses to block signals between the brain and stomach.

That device is much larger and includes an external control unit and batteries that must be recharged frequently. Known as vBloc, or Maestro, it was developed by EnteroMedics, of Roseville, Minnesota, which in 2017 became ReShape Lifesciences and moved to San Clemente, California.

Unlike the vBloc device, the one developed at UW-Madison uses the body’s natural movement to stimulate the vagus nerve only when the stomach moves, Wang said.

“Ours is much smaller and flexible … and has less burden to the human,” Wang said. “Our device is automatically self-controlled.”

In rats, the device was implanted through an incision in the abdomen and attached to the outside of the stomach. In humans, the implantation procedure likely would be minor, Wang said.

Unlike gastric bypass surgery, which permanently shrinks the capacity of the stomach, the UW-Madison weight-loss device is reversible, he said.

Wang has developed other wearable or implantable devices, including a nanogenerator that harvests energy for people’s hearts and a motion-powered bandage to speed healing of wounds.

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