BRIEF: New Fiber Toggles Between Stiff and Floppy

(Inside Science) -- Researchers from Switzerland and Italy have made a new fiber with a heat-controlled split personality -- soft and flexible when warm; strong and stiff at room temperature.

The fiber contains a core of low-melting-point metal alloy encased in a tube of silicone rubber. It can have a diameter as small as a few millimeters, with lengths up to several meters. The threadlike geometry makes a versatile material that can be knitted, knotted, wrapped and woven, the team said.

The fiber acts like a stiff metal wire at room temperature, but when researchers apply current through a thin copper wire coiled around the silicone tube, the metal core melts and the fiber turns floppy. Above 62 degrees Celsius (144 degrees Fahrenheit), the fiber becomes more than 700 times softer and 400 times more deformable than when the core is solid. The material is also self-healing. A broken metal core can fuse itself back together when it is melted.

Threadlike materials that can switch between soft and stiff could come in handy in reconfigurable robots that morph from flying machines to land vehicles. The new material could also be used in medical devices, such as adjustable-stiffness casts and endoscopes.

The new fiber is described in a paper in the journal Advanced Materials.