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

MIT engineers have created soft, 3-D-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. It can even be directed to wrap itself around a small p