The shape-shifting material holds promise for flexible robotics and medicine, said the researchers, mooting tiny devices that can envelop a drug, transport it through the body, and unfold to release it where needed.

A team of US-based researchers made the new type of 3-D printing ink by mixing magnetic iron particles with soft, silicone rubber.

"The menagerie of structures that can be magnetically manipulated includes a smooth ring that wrinkles up, a long tube that squeezes shut, a sheet that folds itself, and a spider-like 'grabber' that can crawl, roll, jump, and snap together fast enough to catch a passing ball," said the Massachusetts Institute of Technology (MIT), whose experts spearheaded the project.

"It can even be directed to wrap itself around a small pill and carry it across a table."

The exploit was reported in the scientific journal Nature.

According to Xuanhe Zhao of MIT's mechanical engineering department, the material can be used to manufacture magnetically-controlled biomedical devices.

"For example, we could put a structure around a blood vessel to control the pumping of blood," he said in a statement issued by the institute.

Or a magnet could be used to guide a tiny device through the gastrointestinal tract to take pictures, extract tissue samples, clear a blockage, or deliver drugs.

This is the latest breakthrough in the quest for a soft, flexible material that can be manipulated to change shape and move.

- 'Fast, forceful' -

Devices made from hydrogels, for example, swell or shrink when temperature or pH changes, while hydraulic devices can be activated when water is pumped into them. So-called "elastomers" stretch when an electric current is applied.

These devices are slow, however, with some requiring hours to change shape, said the research team.

Some must be connected to water or air via tubes, while elastomers require high-voltage electric shocks.

"There is no ideal candidate for a soft robot that can perform in an enclosed space like a human body, where you'd want to carry out certain tasks untethered," said Zhao's colleague, Yoonho Kim.

The new method, he added, is promising "because it is fast, forceful, body-benign, and can be remotely controlled."

Unlike other magnetically-activated materials created so far -- in which iron particles have the same magnetic polarity -- particles in the new method are imbued with differing polarities.

This allows for more complex movements, the researchers reported.

The material can be seen in action here: https://www.youtube.com/watch?time_continue=1&v=aV07hCF7-AQ