I have seen the future, and it is cilia. Yes, you read that right: those trillions of tiny hair-like extensions that carpet every inch of your body could bring scientists’ visions of a universal class of “smart” materials that change and adapt when subjected to various stimuli closer to reality. These artificial cilia could one day do everything from testing drugs and monitoring air quality to measuring glucose levels and detecting electromagnetic fields.

While largely ignored over the past century (or, at best, dismissed as being purely vestigial), scientists are finally beginning to appreciate the many vital functions they perform in and outside of our bodies. Much like an antenna or sensor, cilia gather information from their surroundings and react—by activating a cellular process or shutting down cell growth, for example—if something seems amiss. They can also act as miniature roads or railways, carrying dirt, bacteria and other noxious materials out of our lungs or shuttling a fertilized egg from the ovary to the uterus. And, perhaps most importantly, cilia make it possible for us to see, hear, smell, and otherwise feel the outside world.

Now some researchers believe that cilia-like structures could bring their sensory prowess to medicine, environmental monitoring and a number of other fields. Leading the charge is Marek Urban of the University of Southern Mississippi who has created a copolymer film with hair-like filaments that mimics the functions of normal cilia.

Each of these artificial cilia is equipped with an array of sensors that enable it to respond to the slightest fluctuations in temperature, pH, or light by folding over, shrinking or even changing colors. These unique behaviors are the direct result of molecular rearrangements and conformational shifts in the structure of the copolymers. For instance, when Urban and his colleagues exposed the cilia to hydrochloric acid vapors, they immediately bent towards them and changed colors from yellow to red.

A longer exposure resulted in further bending and a change of color from red to purple. Yet when the researchers switched to using ammonium hydroxide vapors (which have a much higher pH), the cilia reverted to their original shape and color. The cilia similarly responded to variations in temperature and different wavelengths of light by shrinking, modifying their surface morphologies, and becoming fluorescent.

Though more proof of concept than anything else, this work clearly demonstrates the “smart” potential of these copolymers. And, as the NSF release notes, it looks like Urban and his collaborators aren’t wasting any time putting them through more trials and dreaming up new applications. If scientists can further expand their functionality and incorporate them into other technologies (eventually even our bodies), the cilia could become a ubiquitous component of our future everyday lives—helping to treat diseases or simply supplementing our sensory tool set by granting us new abilities.

Images: University of Iowa and Zina Deretsky/NSF

While it may sound unheard of, scientists have been pressing bacteria into service in construction for years. The use of mineral-producing bacteria has already been explored in a variety of applications, including the hardening of sand and in repairing cracks in concrete. But there are two problems inherent to this approach. First, the reaction that these bacteria undergo to synthesize calcium carbonate results in the production of ammonium, which is toxic at even moderate concentrations. The other problem is a more prosaic one. Since the bacteria have to be applied manually, a worker or team of workers would have to go out every few weeks to patch up every little crack on every slab of concrete—nearly defeating the purpose of making the repair process simpler and more cost-effective.

Jonkers’ solution was to track down a different bacterial strain that could live happily buried in the concrete for prolonged periods of time. Because the bacteria would be mixed into the concrete from the start, they could immediately nip small cracks in the bud before they had a chance to expand and become exposed to water, rendering them vulnerable to further wear and tear. (Concrete structures are typically reinforced with steel bars, but these can easily become corroded when water seeps into the cracks.) Such a strain would have to endure the high pH environment of concrete and churn out copious amounts of calcium carbonate without also producing large quantities of ammonium.The researchers found just the right candidates: a hardy bunch of spore-forming bacteria belonging to the genus Bacillus that make a great living in the alkaline soda lakes of Russia and Egypt. Jonkers and his colleagues placed the spores and their food source, calcium lactate, into small ceramic pellets to prevent them from being activated prematurely by the wet concrete mix and adversely affecting the integrity of the material. The spores remained dormant until the formation of a crack allowed water to sneak in, waking the bacteria and their appetite. As they began to chow down, gobbling up the calcium lactate and water, they also began to pump out calcite (a very stable form of calcium carbonate), which quickly went to work filling up the holes. Now that they’ve successfully tested the bacteria’s mettle, Jonkers and his co-workers plan on comparing the strength of their natural concrete to that of the real thing. While not examined in the New Scientist story, I imagine that it should be possible to genetically tweak the bacteria into building a stronger form of calcite (or an even tougher material) that would match up more favorably to its man-made counterpart.

For those of you who would prefer to keep bacteria out of your walls (not that you need to worry, since these particular strains wouldn’t survive outside), there are other alternatives. Michelle Pelletier, an engineer from the University of Rhode Island, has created a microencapsulated sodium silicate healing agent that, like the bacteria, springs into action when a crack begins to appear. The sodium silicate reacts with the calcium hydroxide embedded in the concrete to form a malleable gel that covers the holes and hardens within a week of activation. According to Pelletier, the material may also help ward off corrosion by enveloping the steel bars in a thin, protective film.

Though their approaches to solving the problem may differ, both Jonkers and Pelletier tout the climate benefits of their inventions: Cement production already accounts for roughly 7 percent of worldwide carbon dioxide emission production, so any technology or procedure that could make concrete structures more durable would be a welcome development.

Image: sociotard/Flickr

Despite what you may think, this isn’t actually such an unusual pairing. By virtue of their simple design (most only contain enough genes to encode a few dozen proteins) and infinite capacity for manipulation, viruses have become the favored go-to tool for scientists seeking to explore cellular systems and tinker with their underlying components. Gene therapists have been infecting bacterial, plant, and animal cells with viruses for years in order to shuttle in new genes and repair malfunctioning ones. In one recent application, a team of researchers led by University of Pennsylvania ophthalmologist Arthur Cideciyan restored sight to two blind individuals by injecting a virus equipped with a retinal gene into their eyes.For others, the appeal of viruses lies in their aptitude for genetic engineering. A little over a year ago, a group of MIT scientists led by Angela Belcher successfully transformed the M13 bacteriophage, a virus harmless to humans, into the cathode and anode of a lithium-ion battery. In 2006, the same team had tweaked several of the M13′s genes to make it self-assemble into a negatively-charged paper-thin film that could be used as an anode.

Constructing the cathode proved to be more of a challenge because the materials used to make it needed to be highly conducting—and most such materials tend not to be. To get around that problem, Belcher and her colleagues imbued the viruses with the ability to attract iron and phosphate along their thin, filamentous bodies and paired them up with carbon nanotubes to create dense networks of conductive material.

Unlike conventional batteries, these can be molded to fit any shape and could eventually be sprayed onto a range of other devices. The virus batteries can also be assembled in a more environmentally friendly way: at normal room temperatures and without relying on toxic chemicals. The ease with which researchers can alter their properties—to change the battery’s design or, say, to switch to a better cathode—by simply turning on or off one gene or another only makes them more attractive. This week at the American Chemical Society (ACS) meeting, Mark Allen, a postdoctoral researcher from Belcher’s lab, reported that they had done just that—engineer the virus’ genetic code slightly differently to make an iron fluoride cathode. That’s important because the use of current lithium ion battery technologies is severely limited by their relatively low energy density. Metal fluorides have shown promise because they do a better job of maximizing energy density, particularly when used in the cathode. Their Achilles’ heel is their cycle life, which is much shorter than existing batteries, but some research indicates that infusing them with oxygen could resolve that issue.

Another research group led by James Culver from the University of Maryland announced that it had also made the parts for a lithium-ion battery by using the tobacco mosaic virus (TMV), which infects tobacco plants. In a study published this month, he and his colleagues demonstrated that their virus-built silicon anode had roughly 10 times the capacity of current graphite anodes. One advantage of Culver’s design is that the batteries could eventually be grown (quite literally) in the field by farmers—though that is at least several years away. And while these batteries will initially be developed for the military to lighten soldiers’ loads on the battlefield, there is no reason why they couldn’t eventually make their way into your next shirt or pair of shoes. Perfect for when that invisible dress goes out of style.

Image: Donna Coveney/MIT

The major challenge that scientists face is developing a sensor that is both long-lived and biocompatible. The human body is extremely picky about implants, and will quickly reject or react poorly to most materials found in everyday electronics. Even the materials that make peace with the body’s immune system, like those found in pacemakers, are not always ideal. Some require constant maintenance, while others need to be replaced every few days and are inconvenient to install, to say the least.

But external devices have their own problems. Patients often forget to wear portable devices like glucose monitors, making it more difficult for their physicians to evaluate their condition over extended periods of time. And imagine how annoying it would be to walk around with several monitors because your doctor wanted to track multiple vital signs. A much better alternative would be a single, unobtrusive, and long-lived implant that could detect and measure several chemicals in the body at once.

Fiorenzo Omenetto, a biomedical engineer at Tufts University, may have the solution: a tiny flexible biosensor wrapped in silk and gold. Long-time DISCOVER readers will already be familiar with the many benefits of silk and its numerous potential applications in medicine—there’s a reason we’ve been trying to mass-produce spider silk for years. In addition to being super-tough and stretchy, silk also happens to be a great fit for most tissue surfaces in the body.

What makes gold an appealing component is its unique electromagnetic properties. Along with a number of other highly conducting metals, including silver and copper, gold can be tweaked on a nanoscale level and combined with other materials to respond to frequencies in the terahertz range, which sits at the far end of the infrared range. These artificial composites, called metamaterials, have vaulted into the popular imagination in recent years due to their frequent association with the Harry Potter invisibility cloak.

As it turns out, enzymes and other proteins in the body resonate at specific frequencies within this range (they have their own “T-ray” signatures), making them easy to identify with the right type of antenna—the biosensors. To build the sensors, Omenetto and his colleagues took 1 square centimeter silk film squares and sprayed them with a gold-based metamaterial sheen. They then folded them up into small cylinders and implanted them into muscle tissue. Even buried under several thin slices of muscle, the sensors still resonated at their characteristic frequencies.

The sensor works by detecting subtle changes in the silk substrate that are caused by blood proteins and other chemicals floating around it in the tissue. Once the metamaterial picks up on the molecules’ distinct T-ray signatures, it transmits the information back to the researchers. In the case of a diabetic patient, for instance, the metamaterial would be able to track minute variations in glucose and insulin levels. As Omenetto puts it, the sensor is effectively “a lot of small antennas that behave as one.”

The possibilities of this sensor in research and medicine could be limitless. The ability to detect tell-tale signs of diabetes, cancer and a variety of other severe diseases would make treatments much more effective and tailored to the individual patients. Though the field is still in its infancy, startups like GlySens Incorporated and Physiologic Communications are hoping to capitalize early on the growing wave of interest in this technology. In addition to tracking small-scale changes in protein levels, the sensors could eventually be used as remotes to activate other devices in the body, such as a wireless defibrillator or insulin pump. And there may come a day when we can check our health status via an iPhone app. Of course, I’m still holding out hope for Fantastic Voyage-style mini-submarines to monitor the body, but that’s a different story.

Image: Hu Tao/Tufts University

The composition was imagined by Evegenii Narimanov, a materials engineer at Purdue University, and then created by Mikhail Noginov, a materials physicist at Norfolk State University. (Narimanov recently made some news when he produced the first electromagnetic black hole, capable of slurping up the light waves that come near it.) The mesh is placed at intervals smaller than the wavelength of the radiation it needs to be absorbed. The new material reflected as little as less than one percent of the sub-infrared, 900-nanometer-wavelength radiation, though Narimanov said the effect would be the same at any wavelength —- including the visible light spectrum —- under other configurations. Narimanov told New Scientist he anticipates the material will find its use in coating stealth fighters to improve their invisibility to radar.

The battle for blackness has been going on for some years now. In 2003, scientists and the United Kingdom’s National Physical Laboratory created a coating that reflected 25 times less light than ordinary paint. The substance, made from a pitted surface of a nickel alloy, was intended to be used on the inside of binoculars and telescopes, to reduce interference. At the time, Dr. Richard Brown, lead scientist for the project, told the BBC, “It’s a very interesting surface to look at because it’s so black.”

Imagine how hard he’ll stare at  the new black.

Will we use metal in the future? What else would we build things out of? Might we use organic technology (machines and buildings made of or from biological organisms) instead?”
In The Graduate, that iconic film from 1967, bewildered 20-something Benjamin Braddock (Dustin Hoffman) gets some career advice from a businessman who leans close and intones “I want to say one word to you. Just one word. Are you listening? Plastics.” Benjamin didn’t follow that advice, but the rest of the world did, and in spades. By 1979, global production of plastic had exceeded that of steel and is still growing, reaching over 200 million tons this year. There’s no doubt that plastic will continue to play a major role in how we make things, but it won’t replace everything.

In some ways, plastic is the material of the future, the latest step in humanity’s long upward trek through the ages of stone, bronze, iron, and steel. The word “plastic” comes from Greek roots meaning “capable of being molded.” Compared to metals and other materials, plastic is infinitely versatile. With its ability to shape-shift and to take on different mechanical and optical properties, it shows up in a huge spectrum of applications from packaging and plumbing to toys, medical supplies, and computers. And unlike iron and steel, plastic doesn’t rust.

But plastic also has problems that will prevent it from replacing metals any time soon. Its very durability can be an issue. Discarded plastic objects can survive for centuries in garbage landfills without degrading, and plastic artifacts have been found polluting the oceans far distant from any land. Also, what doesn’t seem to be widely appreciated, the raw material to make plastic comes from a resource we need to conserve, petroleum.

On top of this, metals do some things better than plastic—just try cutting up an apple with a plastic knife. Copper and other metals are needed to conduct electricity through power grids; all plastic can do is insulate the current-carrying wires. However, plastic is making inroads relative to some materials such as wood, which is being replaced by plastic “lumber” in certain applications.

Plastic also offers a possible way to actually construct things using biotechnology. Unlike metals, which are classified as inorganic, plastics are organic; they’re made of carbon, hydrogen, nitrogen, and oxygen, the same constituents as living things, which links plastic to biological products. For instance, under the right conditions, certain microorganisms can synthesize compounds called polyhydroxyalkanoates (PHAs). These display properties like those of artificial plastics, with the benefits that they’re not petroleum-based and are biodegradable. Researchers are investigating ways to mass-produce these bioplastics, for instance by bioengineering plants to create them.

If you want to speculate even further, way past the idea of growing plastic rather than making it in factories, think about the science-fictionish possibility of bioengineering plants to produce plastic exactly in a desired shape from a drinking cup to a house. Current biotechnology is far short of this possibility, but science fiction has a way of pointing to the future. If bioplastics are the materials breakthrough of the 21st century, houses grown from seeds may be the breakthrough of the 22nd.