Out: 3-D printing. In: 4-D printing?

Are you experimenting with these materials or are you creating your own programmable materials?
We use some of these materials, but we try not to rely on them because they’re expensive and already come with defined properties. We would rather use everyday materials like plastics, metals and woods, and combine them in smart ways. Our vision for 4-D printing was to combine and print these materials in different thicknesses and orientations. Thicker materials change properties slower after being printed but proved to be stronger, whereas thinner materials change quickly but are weaker. When combined, these different material properties react differently to their environments—whether they’re placed in light, water or some other medium—in a way that could mimic the movement of machine-assembled devices driven by actuators, motors and sensors.

When you talk about programmable materials containing information about the assembly process, what type of information are you talking about?
This information is in the form of a material’s properties, its shape (or geometry) and the amount of energy used to initiate self-assembly. One of our materials, for example, has properties that cause it to expand and change shape when you dip it in water. To maintain control over how the material changes, we designed it with a particular geometry that determines the direction it will curl, the number of times it will curl and the angles at which it will curl. Now we need to make the material more intuitive to use and easier to control.