The Year in Materials
Stretchable electronics and the strongest material ever were just two achievements of 2008.
Graphene, the material behind one of our 10 emerging technologies of 2008, stayed in the news all year. In July, researchers who poked the single-atom-thick carbon sheets with the tip of an atomic force microscope confirmed that graphene is the strongest material ever tested. But most of the graphene community, including Kostya Novoselov, one of the first to make graphene and one of TR’s top 35 innovators under 35 in 2008, is interested in graphene’s electrical properties. Last month, two separate groups of researchers reported that they had made fast graphene transistors that could be used for wireless communications. Other researchers addressed the problem of manufacturing graphene. Novoselov and his collaborators originally made the single-atom-thick hydrocarbon sheets by crushing graphite between two layers of tape. But more scalable graphene-manufacturing technologies will be needed for the material to be adopted by the chip industry. One group at the University of California, Los Angeles, developed a simple method for making large sheets of graphene by dissolving graphite in hydrazine.
Nanomedicine and Nanomaterials Safety
Researchers made a number of advances in understanding how to make nanomaterials that take a drug straight to diseased cells in the body, which should improve the efficacy and safety of therapies for cancer and many other diseases. They found that nanoparticles shaped like bacteria did a better job getting inside cells, and developed ways to get drugs to the right subcellular machine. And they made major progress in developing agents to deliver RNA. Delivery has been one of the biggest obstacles to a promising therapeutic technique called RNA interference, which uses strands of RNA to muffle the activity of disease genes. A method for screening large numbers of fatty-molecule carriers allowed the company Alnylam Pharmaceuticals to make carriers for delivering RNA to respiratory cells and other targets in mice.
However, there was some bad news this year about the safety of nanomaterials. Two studies in mice suggested that carbon nanotubes could behave like asbestos in the lungs, causing cancer. Whether the nanotubes can, like asbestos, be easily inhaled is just one of many remaining questions. Nanomaterials are diverse in their chemistry and structure, and it’s difficult to make generalizations about their safety. One study this year attempted to address this diversity. Researchers developed a method for screening a diverse group of nanomaterials in large numbers and in many kinds of human cells.
Stretchable, Flexible, Wearable Electronics
Other researchers integrated carbon nanotubes into a number of devices. Researchers in Japan made a stretchy electronic circuit by adding carbon nanotubes to a polymer, creating a material that could be used to make stretchable displays and simple computers that wrap around furniture. In China, researchers made thin, transparent, flexible speakers from carbon nanotubes. And researchers in Illinois made stretchable silicon electrical circuits whose performance equals that of their rigid counterparts.
By coating cotton thread with a mixture of carbon nanotubes and a conductive polymer, researchers in Michigan made fabrics that can perform sophisticated computation and act as wearable biosensors whose sensitivity to biological molecules rivals that of conventional diagnostics.
Tough, Strong, and Sticky
Some of the year’s coolest new materials were made possible by mimicking the nanoscale features of natural structures. For years, researchers have been trying to make materials that are as tough as nacre, the material that lines abalone shells, with limited success. This year, materials scientists created a new ceramic that’s better than nacre; it could eventually be used as a structural material for buildings and vehicles. Like nacre, the new ceramic is a composite of a hard material and a gluey one. Researchers have also finally outdone the gecko, which uses arrays of nanoscale hairs on its paws to scale walls and ceilings. Arrays of carbon nanotubes with two layers–one vertically aligned, the other tangled–mimic gecko-foot structures but are 10 times as sticky.
Super-Resolution Imaging and a $10 Microscope
Metamaterials are usually lauded for their potential to direct light around an object, completely hiding it. This year brought the first designs for acoustic metamaterials, which will shield objects from sound. But the earliest application of metamaterials, usually made up of metals carefully structured on the nano- or microscale to tailor their interactions with light, is likely to be in super-resolution imaging. Light microscopes with resolutions on the scale of biological molecules will help biologists understand not just what proteins are at work in diseased cells, but also how they interact with other molecules to cause disease. Nicholas Fang of the University of Illinois is using metamaterials made up of metals structured on the nanoscale to make superlenses, which increase the resolution of biological light microscopes by an order of magnitude.
Other groups are taking a different approach to super-resolution imaging, developing new fluorescent probes and new optical systems to make the inner workings of cells visible. The highest-resolution 3-D light microscope ever made allowed researchers to see the inner workings of the metabolizing mitochondria, the subcellular organelle that powers cells, for the first time.
Meanwhile, a $10 microscope developed this year at Caltech uses cheap starting materials, including microfluidics and the same light-sensing chips found in digital cameras. Its imaging quality equals that of conventional microscopes. If integrated into a PDA, it could bring sophisticated imaging technology to rural doctors.
This year, researchers at Tufts University demonstrated that they can use proteins from silkworm cocoons to make biodegradable optical devices. They hope that their devices will eventually be implanted during surgery and used to monitor patients for signs of recovery.
The year also saw advances in materials for tissue engineering. It’s been difficult to mimic the structures of the heart, liver, and other tissues in the lab. A stretchy polymer developed at MIT can withstand the mechanical stresses of beating heart tissue, and its honeycomb structure encourages heart-muscle cells to orient naturally, which makes for heart-tissue patches that contract like real heart muscle.