September_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | S E P T E M B E R 2 0 2 0 1 3 DESIGNING SHAPE- MORPHING DEVICES Research out of Harvard’s John A. Paulson School of Engineering and Applied Sciences (SEAS), Cambridge, Mass., provides a new platform for the design and application of shape-mor- phing devices. Scientists designed materials that can control and mold a balloon into preprogrammed shapes using kirigami sheets—thin sheets of material with periodic cuts—embedded into an inflatable device. As the balloon expands, the cuts in the sheet guide the growth, permitting expansion in some places and constricting it in others. The researchers were able to control the expansion not only globally to make large-scale shapes but also locally to generate small features. The team also developed an in- verse design strategy, an algorithm that finds the optimum design for the kirigami inflatable device that will mim- ic a target shape upon inflation. An in- dividual cut on a sheet contributes to the larger shape of the balloon, much like a pixel helps form an image on a 2D surface. The researchers found that by tuning the geometric parameters of these cuts, they could control and em- bed complex shapes. To demonstrate this, they programmed a balloon to mimic the shape of a squash complete with the characteristic bumps and ridg- es along the side. Next, the researchers aim to use these kirigami balloons as shape- changing actuators for soft robots. The work lays a foundation for the design of structures at multiple scales, from mi- cro minimally invasive surgical devices to macro structures for space explora- tion. seas.harvard.edu. WORLD’S LIGHTEST SHIELDING MATERIAL Researchers at Empa, Switzerland, are using cellulose nanofibers as the ba- sis of a new aerogel. The work produced a composite of cellulose nanofibers and silver nanowires, creating ultralight fine structures that provide excellent shield- ing against electromagnetic radiation. The effect of the material is significant— it intercepts virtually all radiation in the frequency range of high-resolution ra- dar radiation. The correct composition of cellu- lose and silver wires in addition to the material’s pore structure is essential to the shielding effect. Within the pores, EMERGING TECHNOLOGY Norman Noble Inc., Highland Heights, Ohio, started improvements on a new 50,000-sq-ft facility at its headquarters. The facility will pro- vide additional manufacturing space to meet medical OEM customers’ growing requirements for products, including Nitinol-based structural heart implants and neurovascular devices as well as multileaf collimator assemblies used in cancer radiation therapy equipment. The new space is scheduled to be operational in late 2020. nnoble.com. BRIEF Programmable balloons could pave the way for new shape-morphing devices. Courtesy of Bertoldi Lab/Harvard SEAS. the electromagnetic fields are reflected back and forth and trigger electromag- netic fields in the composite material, which counteract the incident field. To create pores of optimum size and shape, the researchers pour the mate- rial into precooled molds and allow it to freeze out slowly. The growth of the ice crystals creates the optimum pore structure for damping the fields. With this production method, the damping effect can be specified in different spatial directions. Shielding structures cast in this way are highly flexible. Even after being bent back and forth a thousand times, the damping ef- fect is practically the same as with the original material. The desired absorp- tion can be easily adjusted by adding more or less silver nanowires to the composite as well as by the porosity of the cast aerogel and the thickness of the cast layer. In relation to the weight of the material, no other material can achieve such shielding. This ranks the titanium carbide nanocellulose aerogel as by far the lightest electromagnetic shielding material in the world. www. empa.ch/web/empa. A sample of Empa’s electromagnetic shielding material—a composite of cellulose nanofibers and silver nanowires.