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An untethered miniature origami robot that self-folds, walks, swims, and degrades,was presented at ICRA 2015 in Seattle - .PDF file.
This week’s video shows how a sheet can self-fold into a functional 3D robot, actuate immediately for untethered walking and swimming, and then dissolve in liquid.
In use, the robot could be used in medical applications but making one as agile – and disposable – as this one has proved challenging.
According to its developers from MIT and TU Munich, the sheet weighs 0.31g, spans 1.7cm square in size, features a cubic neodymium magnet, and can be thermally activated to self-fold. They add that since the robot has asymmetric body balance along the sagittal axis, the robot can walk at a speed of 3.8 body-length/s being remotely controlled by an alternating external magnetic field.
Developed models include an acetone-degradable version, which allows the entire robot’s body to vanish in a liquid.
Shuhei Miyashita, Steven Guitron, Cynthia R. Sung, and Daniela Rus from MIT and Marvin Ludersdorfer TU Munich describe how they developed with robot in a paper titled: An untethered miniature origami robot that self-folds, walks, swims, and degrades.

I see this as interesting, and remarkable, but how is the thing supposed to know where the open beaker of acetone is to be found out in the field. LOL
Fascinating though the little things are to watch, they seem to rely on a fluctuating external magnetic field, supplied by four big coils under the table, for their power and control intelligence. The use of “self” to describe them is therefore somewhat questionable.
Would not the solvents that dissolve the “entire robot’s body” leave the magnet?