December 2018
Vol 4, Issue 12

About The Cover

Cover image expansion

COVER Cellular structures found in nature are often imitated in synthetic materials like polymeric and metallic foams. New technologies like four-dimensional printing are being used to create cellular structures with various characteristics that display unique mechanical, functional and thermal properties. These materials—known as metamaterials—generally do not respond to a changing environment because the material and architecture are fixed in time after their creation. Seeking a material that better adjusts to the stimuli in their environment, Jackson et al. incorporated magnetorheological (MR) fluid suspensions into three-dimensional-printed polymer tubes to create a new class of FRMMs. The MR fluids line up under a magnetic field, thus making them stiffer. The authors demonstrated their approach by printing cuboctahedron unit cells with controlled fluid delivery methods and testing them in a custom device in which the magnetic field strength could be specially regulated. They found that the average response time when hardening was less than a second and, when turned off to soften, was less than a quarter of a second. The researchers further developed a model to predict the responsiveness of their FRMMs in different conditions. [CREDIT: JULIE A. JACKSON]