This week's Question: While 3D printing has still not yet reached the mainstream, MIT and other researchers are performing primary tests on the next design dimension. 4D printing, a self-assembly design process, enables the production of composite materials that react and change shape in predictable ways when exposed to external elements such as water. A printed rear wing, for example, would have the ability to transform its aerodynamics during a downpour. Autonomous pipes, too, could expand and narrow based on flow. Self-assembling technologies may eventually allow the construction of space structures whose components deposit themselves in zero-gravity environments without human intervention. Wood and carbon fibers have responded well to 4D testing, but more materials and energy sources are likely required for the materials to self‑optimize according to sensing and logic. What do you think? Will "4D" materials catch on?