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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 1 9 9 CARNEGIE MELLON’S ENHANCED FLEXIBLE MATERIALS Scientists from Carnegie Mel- lon University, Pittsburgh, have devel- oped a new process to create a class of stretchable polymer composites with enhanced electrical and thermal prop- erties. These materials are promising candidates for use in soft robotics, self- healing electronics, andmedical devices. The new methodology uniform- ly incorporates eutectic gallium indi- um (EGaIn), a metal alloy that is liquid at ambient temperatures, into an elas- tomer. This process creates a new ma- terial—a highly stretchable, soft, multi- functional composite that has a high level of thermal stability and electrical conductivity. Using atom transfer radical po- lymerization, scientists can connect monomers in a piece-by-piece fashion, resulting in highly tailored and consis- tent polymers with specific properties. “We can now suspend liquid metal in virtually any polymer or copolymer in order to tailor their material properties and enhance their performance,” the scientists say. “This has not been done be- fore. It opens the door to future materials discovery.” The researchers envision that this process could be used to combine different polymers with liquid metal and, by controlling the concentration of liquid metal, they can control the properties of the materials they are creating. They believe that with the help of artificial intelligence, their approach could be used to design “made-to-order” elas- tomer composites that have tailored properties. The result will be a new class of materials that can be used in a variety of applications, including artifi- cial skin, soft robotics, and bio-compat- ible medical devices. cmu.edu . METALLICITY: A NEW UNDERSTANDING OF MATTER New possibilities in materials de- sign are now within reach following the discovery of unexpected particle be- havior. Researchers from Northwest- ern University, Evanston, Ill., found that nanoparticles engineered with DNA in colloidal crystals—when extremely small—behave just like electrons. “We have never seen anything like this before,” says Northwestern’s Monica Olvera de la Cruz, who made the initial observation through com- putational work. “In our simulations, the particles look just like orbiting electrons.” With this discovery, the research- ers introduced a new term called “me- tallicity,” which refers to the mobility of electrons in a metal. In colloidal crys- tals, tiny nanoparticles roam similarly to electrons and act as a glue that holds the material together. “This is going to get people to think about matter in a new way,” says scientist Chad Mirkin. “It’s going to lead to all sorts of materials that have po- tentially spectacular properties that have never been observed before. Properties that could lead to a variety of new technologies in the fields of op- tics, electronics, and even catalysis.” “In science, it’s really rare to dis- cover a new property, but that’s what happened here,” Mirkin says. “It chal- lenges the whole way we think about building matter. It’s a foundational piece of work that will have a lasting impact.” northwestern.edu. NANOTECHNOLOGY BRIEF Grafoid, Canada, recently launched Grafprint3D Inc., a new company with a focus on production for the worldwide additive manufacturing market based on Grafoid’s proprietary MesoGraf technology. The initial key application target markets include wearable device fabrication with biocompatible polymers, biomaterial substrates for cell therapy engineering research, and rapid product prototyping with printable advanced nanomaterials. grafoid.com. Northwestern researchers discovered that programmable atom equivalents (PAEs)—when reduced in size and DNA grafting density—behave similar to elec- tron equivalents (EEs), roaming through and stabilizing the lattices defined by larger PAEs, as electrons traditionally do in metals. Left: This single liquidmetal nanodroplet was grafted with polymer chains. Right: A depiction of polymer brushes grafted from the oxide layer of a liquidmetal droplet. Courtesy of Carnegie Mellon University.