How could you build an artificial tadpole? Or simulate the motion of a cilium? Those would be hard to do with mechanical means — even micromechanical because of their fluid motion. Researchers have been studying shape-programmable matter: materials that can change shape based on something like heat or magnetic field. However, most research in this area has relied on human intuition and trial and error to get the programmed shape correct. They also are frequently not very fast to change shape.
[Metin Sitti] and researchers at several institutions have found a way to make rapidly changing silicone rubber parts (PDF link) that can change shape due to a magnetic field. The method is reproducible and doesn’t seem out of reach for a hackerspace or well-equipped garage lab.
The paper is full of math, but the basic idea is simple. The math part is determining the magnetization profile required for the shape change required. For example, one of the test objects curled a beam into a semi-circle using 100 distinct shapes over time . The math tells you what profile you need and the magnetic field required to actuate it.
The researchers used a silicone rubber known as Ecoflex. They mix aluminum granules with some of the rubber and neodymium-iron-boron particles with the remainder. They create a mold for the part they want to make — a great use for a 3D printer. Then they cast the passive part of the shape using the rubber/aluminum mix. Once cured, a laser cutter creates a channel for the active part of the shape, which is cast using the magnetic rubber material.
It is important that both mixtures have the same elastic modulus, and the amount of material added apparently took some trial and error. (Oh sorry, this is a scientific paper, so it was “experimentally characterized”.) Once the material is ready, it is pressed in a jig, another good chance to turn on the 3D printer, that holds the desired shape. The whole assembly is exposed to a strong magnetic field which serves to program the shape.
Armed with a 3D printer, a laser cutter, and some basic chemical handling gear, this is an interesting place where someone could still contribute to the state of the art. The method only works for essentially 2D objects, but the team wants to investigate 3D versions. In addition, they are unable to work with shapes less than about a millimeter, so there’s plenty of room for new experimentation.