Magnetic 3D-printed structures crawl, roll, and jump

Engineers have created soft, 3D-printed structures whose movements can be controlled with a wave of a magnet, much like marionettes without the strings. 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.