Science Concentrates ELECTRONIC MATERIALS
Strong graphene aerogels bounce back Plant-inspired materials are strong, elastic, and conductive
A graphene aerogel recovers after being squished by an object more than 6,000 times its weight.
graphene aerogel, 10 mm on a side, using strength, superelasticity, and conductivity Ultralight and exceptionally strong, a specialized freezing technique for creatin an aerogel requires carefully designed, graphene aerogels are attractive materials ing structured porous materials that Bai ordered structures, says Hao Bai of Zhejifor use as catalysts, electrodes, and flexhelped develop in 2015 while at Lawrence ang University. He and his colleagues took ible electronics. But one property that’s Berkeley National Laboratory. The method inspiration from Thalia dealbata, an aquatneeded for those applications has been ic plant with strong and flexible stems that uses ice as a template to freeze a suspenhard to impart to the materials: elasticision of graphene oxide such that parallel allow the plant to withstand wild winds. ty. Researchers have now overcome that graphene oxide sheets form, connected The stems are built out of concentric layhurdle by making a squishable graphene by bridges as in T. dealbata. Freeze-drying ers of 100- to 200-µm-diameter structural aerogel that mimics a bendable aquatand warming the sample transformed the tubes, connected to each other by thinner, ic plant’s highly ordered inner porous material into graphene, producing the 1-mm-long bridges that act like springs. structure (ACS Nano 2017, DOI: 10.1021/ aerogel. The researchers sought to replicate the acsnano.7b01815). In addition to being strong and elastic, plant’s properties with a similar strucThe new, conductive aerogel springs the material is highly conductive, considture in an aerogel. They made a cube of back to its original shape after being ering its low density, Bai notes. squeezed to half its size with an This is a clever, low-cost, object more than 6,000 times its and scalable freezing process to weight. The aerogel retains 85% generate a new aerogel microof its original strength even after structure, says Peter Pauzauskie being squeezed more than 1,000 of the University of Washington. times. In comparison, typical The microstructure “would be aerogels with random pore strucvery expensive and difficult to tures that the researchers made achieve” using other methods, inand tested lost more than half cluding three-dimensional printtheir strength after just 10 coming, he says.—PRACHI PATEL, pression cycles. The ordered structure of a graphene aerogel (left) mimics Combining low density, that of a strong, flexible aquatic plant stem (right). special to C&EN
CHEMICAL COMMUNICATION
C R E D I T: ACS N A NO ( B OT H)
Dopamine sends immune signals too Nerve cells often communicate chemically. One cell releases packets of molecules called neurotransmitters, which then influence the behavior of another neuron. Dopamine is one such neurotransmitter known to carry signals in brain circuits involved in rewarding behavior and motor control. Now scientists report that dopamine also ferries messages between immune cells outside the brain to promote antibody production (Nature 2017, DOI: 10.1038/nature23013). When a pathogen invades the body, immune cells that recognize the threat become active and migrate to lymph nodes
or the spleen. Once there, activated T cells and B cells “talk” to each other through immunological synapses—similar to the structures used in nerve cell communication. The conversation between the cells further activates them, including triggering the B cells to mature and start producing antibodies to clear the infection. Ilenia Papa and Carola G. Vinuesa of the Australian National University and coworkers studied immune cells from human tonsils, spleens, and lymph nodes and determined that the T cells in the samples contained granules filled with dopamine. These granules are similar to those carry-
ing dopamine and related neurotransmitters in nerve cells. In cell culture experiments, the team found that human B cells exposed to dopamine move proteins important in immune responses to their surfaces. This triggers a feedback loop that helps strengthen the synapses between T cells and B cells and pushes the B cells to mature. The findings, Papa says, could lead to strategies to enhance dopamine signaling to boost vaccination responses or to disrupt it to block the production of autoantibodies in autoimmune diseases.—MICHAEL TORRICE JULY 17, 2017 | CEN.ACS.ORG | C&EN
7
