An "origami robot" that unfolds itself to perform remote-controlled surgery in the stomach has undergone laboratory tests.

The small rectangular device, swallowed in a dissolvable capsule, is steered by magnetic fields and can crawl across the stomach wall to patch a wound or capture foreign material.

One of its uses could be to remove potentially harmful swallowed button batteries, said the US researchers.

Each year, 3,500 cases of batteries being swallowed are reported in the US alone.

The robot is folded like an accordion when enclosed in the capsule. It contains a magnet that not only responds to external magnetic fields, but can also be used to pick up a button battery.

Lead scientist Professor Daniela Rus, from Massachusetts Institute of Technology in the US, said: "It's really exciting to see our small origami robots doing something with potential important applications to health care.

"For applications inside the body, we need a small, controllable, untethered robot system. It's really difficult to control and place a robot inside the body if the robot is attached to a tether."

The robot was tested in the laboratory in artificial simulations of the human stomach and oesophagus.

The team designed to robot to travel easily through the fluid-filled stomach, and to compress sufficiently to allow it to fit into a capsule that can be swallowed.