Roll, jump and even grab objects. The small flexible robots described in “Nature” by Xuanhe Zhao and colleagues from the Massachusetts Institute of Technology can do this and more. Made with a new “programmable material” thanks to an innovative 3D molding technique, these automata have the ability to transform quickly and reversibly when an external magnetic field is applied.
In essence, the technique described by the authors consists in printing a silicone rubber in three dimensions in which nanoparticles are immersed, consisting of a ferromagnetic material, that is, it has the property of magnetizing and maintaining polarity for a long period of time, if subjected to an external magnetic field (they are used for example to make common magnets). The peculiarity is that in this case the initial polarity is set directly from the printer nozzle.
This allows the nanoparticles to be aligned so as to predict how they will react later by applying magnetic fields. It is possible, for example, to transform their static form or make them move dynamically. Because the material is elastic, it returns to its original shape when the magnetic field is removed.
The authors have demonstrated the capabilities of their technique by creating a small soft six-legged robot, similar to a spider. By applying various magnetic fields, the robotic spider was able to advance by walking on its paws, rolling, carrying medicine pills, or grabbing and returning a fallen object.
A second prototype, based on the same technology, is able to do so
make a horizontal jump of 12 centimeters: a first magnetic field applied in one direction collapses the structure, a second field extends the “legs”, producing the jump.
Soft robots controlled by the magnetic field
The “spider” has changed shape, contracting its legs, due to an external magnetic field (Credit: Yoonho Kim & Xuanhe Zhao)
The prototype, like other devices based on soft materials that change shape in response to physical stimuli such as heat, light or the magnetic field, has many potential applications, for example in medical applications: for example, it could operate in closed spaces being controlled by remote. Another idea is to design a reconfigurable electronic circuit at will.
The new printing method has some advantages that could facilitate its dissemination. The first is that it could be adapted to a wide variety of silicone rubbers and also hydrogels, containing different types of ferromagnetic materials. The second is that it is an inexpensive manufacturing process and not very different from conventional 3D printing.