To make these architectures, we start by growing a coral structure (red). We then nucleate the green stems inside the cavities of the coral structure. While the stems are growing, we open them with a CO2 pulse (purple). (False colored SEM image) This image relates to a paper that appeared in the May 17, 2013, issue of Science, published by AAAS. The paper, by Wim L. Noorduin at Harvard University in Cambridge, MA, and colleagues was titled, "Rationally Designed Complex, Hierarchical Microarchitectures."