Thanks to techniques for manipulating materials at the nanoscale and modifying the matter molecule by molecule in the laboratory, engineers are creating new materials with properties worthy of the boldest imagination of science fiction writers.
Although this image may look like a photomontage, the truth is that there’s no trick. What’s floating in the cup, on top of the cappuccino foam, is nothing other than a piece of 20-carat gold, or more precisely, gold foam, a revolutionary material a thousand times lighter than the golden metal—and almost as graceful as air—but impossible to distinguish from solid gold with the naked eye. In chemical terms it’s called an aerogel, composed of 98% air with only 2% solid material. Its creators have proposed using it in watchmaking and jewellery, but, more generally, the emerging field of noble metal aerogels promises interesting applications in catalysis, electronics and the manufacture of biosensors.
Both “Q”, the creator of gadgets and inventions for the famous spy 007, and the designers of superhero costumes, would be eager to get their hands on a piece of the ultra-strong material that engineers at the Universities of California and Riverside (USA) are working on, which mimics the mantis shrimp, the animal with the strongest and most impact-resistant weapon known to man. This Indo-Pacific crustacean can shatter a snail shell or the glass wall of an aquarium with just one blow from its front appendages. Their strength is due to a herringbone structure that, if emulated, could be used to build a new generation of armour and automobiles that are almost indestructible, or at least have a higher impact resistance than commercial aircraft components. This is an example of biomimetics, imitating nature to obtain materials with new properties.
Seeking the cloak of invisibility
An invisibility cloak that makes 3D objects disappear from view seems more at home in the fantasy stories of the Harry Potter saga than in real life. However, scientists at the Lawrence Berkeley National Laboratory (USA) are working to make it possible. For them, the magic lies in the gold nanoantennas from which they create a thin membrane 80 nanometres thick. Placed on a microscopic object, this cloak redirects light waves of a particular wavelength— in the far red—so that the bulge caused by the object disappears in light of this colour. Although these materials do not yet work with larger objects or a wider range of colours, the researchers have not lost hope. “It is potentially scalable for hiding macroscopic objects,” said Xiang Zhang when announcing the milestone in Science.
Rigid and flexible may no longer be antonyms, at least in the field of materials science. These two properties, at first glance incompatible and opposed, have been twinned in a surprising metallic foam created by Rob Shepherd, a researcher at Cornell University (USA). Working with silicone foam and an alloy of indium, tin and bismuth, Shepherd and his team have created a rigid metal-like material that, when heated to 62°C, can change shape and become ductile and flexible like rubber. The US Air Force, which funded part of the project, intends to use it in the design of mini-aircraft so that they can, for example, dive into water in mid-flight. This research lies in the field of soft robots, machines whose materials make them similar to living organisms.
Metal Elastomer Composite from Ilse Mae on Vimeo.
What if, every time the sun went down, instead of switching on streetlamps and spotlights to liberate buildings from the darkness of night, concrete structures could emit their own glow? This is not a utopic idea, but rather the brainchild of José Carlos Rubio at the Michoacan University of Saint Nicholas of Hidalgo (UMSNH) in Mexico. The researcher has spent nine years modifying the microstructure of cement to achieve a phosphorescent material that absorbs solar energy during the day and returns it at night. Even better, it retains its properties for 100 years. The material is already being tested in paving and signage that emits light without consuming electricity.
Lighter than a feather
Could a dandelion support the weight of a computer chip? Only if it is made from the ultra-lightweight metallic microlattices created at the University of California. Using an innovative manufacturing process, a team led by Tobias Schaedler developed an extremely lightweight metallic compound that is 99.99% air. The 0.01% of solid material (nickel and phosphorus) has been manipulated at the nanoscale to weave a kind of lattice of interconnected hollow tubes whose walls are only 100 nanometres thick, i.e. a thousand times thinner than a human hair. And yet, despite its lightness, the new metal is tough, can be compressed and recover its shape, and withstands thermal stress, vibrations and high pressures, as well as electric shocks. The potential applications include the automotive sector, aircraft manufacturing or even as scaffolding for bone regeneration.
Imagine a glue as strong as the union between the cartilage and the bone in your skeleton and composed of 90% water. That’s how powerful the transparent and highly flexible adhesive hydrogel is that has been developed by engineers at the Massachusetts Institute of Technology (MIT) in the USA. For the first time, there is an artificial glue that surpasses the adhesive capacity of the natural glue with which mussels cling to rocks and the surface of ships, even on non-porous materials such as glass, silicon, titanium or aluminium. As it is biocompatible, in addition to having uses on ships and submarines, it could also be used to make catheters, sensors and biomedical implants. In fact, these bioadhesives are already being used to create a tape that replaces surgical sutures and allows tissue to be sealed in seconds, either to close wounds or to secure implants inside the body.
The days may be numbered for windows made of glass if the original material created by Swede Lars Berglund—a transparent wood—is successful. According to an article in the journal Biomacromolecules, to achieve this feat Berglund first eliminated from the wood the lignin, a component of the plant cell wall that provides opacity. Next, he manipulated the wood at the nanoscale to impregnate the pores with a transparent polymer. The optical properties of the polymer and the lignin-free wood merged and—voilà!—he obtained a transparent wood that is strong, durable, inexpensive, made from renewable resources and crystalline. What more could you ask for? Research into transparent wood is currently in full swing, as this material is expected to have great applications in construction as a substitute for glass that is stronger, safer and a more energy-efficient insulator.
The blackest black
Black Is Black sang the Spanish beat music group Los Bravos in the 1960s, but something that seems obvious is perhaps anything but. Since black is the total absence of light, something that no material can ever completely achieve, no Black is actually Black. In 2014, the British company Surrey NanoSystems unveiled Vantablack, a carbon nanotube material that absorbs 99.965% of visible light. But although Vantablack, created for military and astronautical applications, entered the Guinness Book of Records and BMW even painted one of its vehicles with it, the title of blackest black was short-lived; in 2019 researchers at MIT created by pure chance another material 10 times blacker, absorbing up to 99.995% of light. As a playful demonstration, they used it to completely obscure a $2 million diamond, the brightest material on Earth. Now, Black Is Blacker.
If there is one thing all of the above materials have in common, it’s that they are inert, despite their amazing properties and the fact that some of them were once alive, such as wood. But this need not always be the case. Research is progressing in the field of living materials that combine polymers with living cells or use genetically modified living cells to create the materials themselves. Another approach, pioneered by researchers at Cornell University, is to use biomolecules such as DNA to create materials that are not truly alive—but almost—as they use their own artificial metabolism to assemble, regenerate and move. These materials have the potential to create organic robots that blur the boundary between the living and the non-living.