We did a post on the use of nanotechnology in the textile industry about two years ago, and new research has just settled the long-standing controversy over the mechanism by which silver nanoparticles (the most widely used nanomaterial in the world) kills bacteria. You know, all those new textiles that advertise that they’re bacteria and odor free – they are even claimed to prevent colds and flu and never need washing! Not to keep you in suspense: the research comes with a warning: use enough. If you don’t kill the bacteria, you make them stronger. In honor of this new study (summarized below) we’re re-posting our previous posts on nanomaterials:
Recently, I have been noticing various products claiming to have some kind of nanotechnology-based credential. Turns out that’s because the nanotech tsunami is just gaining steam – one tally says that over 10,000 products using nanotechnology are already on the market. In the food industry, the FDA says there are no nano-containing foods on the market in the U.S., yet DK Matai, Chairman of the Asymmetric Threats Contingency Alliance, says that the USA is the world leader in nano foods, followed by Japan, Europe and China. The Environmental Working Group has done it’s own count of lotions, creams, sprays, washes, cosmetics and nutritional supplements on the market in the U.S. and has found close to 10,000 that contain nanoparticles. And there’s an app for that: The Project on Emerging Nanotechnologies has an iPhone app called findNano, which urges users to photograph and submit information on a possible nanotech product for inclusion in its inventory.
Turns out that there are many who think the next Industrial Revolution is right around the corner – because of nanotechnology. They think that nanotechnology will radically transform the world, and the people, of the early 21st century. It has the capacity to change the nature of almost every human-made object. Whether that transformation will be peaceful and beneficial or horrendously destructive is unknown. So naturally it’s become very controversial. More about that later.
It seems the better term is really nanoscience. Nanoscience is the study of things that are really really small: A nanometer is one billionth of a meter (10-9 m). This is roughly ten times the size of an individual atom. For comparison, 10 NM is 1000 times smaller than the diameter of a human hair. How small is that? “If a centimeter is represented by a football field, a nanometer would be the width of a human hair lying on the field,” offers William Hofmeister of the University of Tennessee Space Institute’s Center for Laser Applications.
Nanoparticles are bits of a material in which all three dimensions of the particle are within the nanoscale: nanotubes have a diameter that’s nanosize, but can be several hundred nanometers (nm) long or even longer. A cubic centimeter of material, about the size of a sugar cube, has the same surface area of a half a stick of gum. But if you fill that cube with particles that are 1 nanometer in size, the surface area of all those particles is an astonishing 6,000 square meters, nearly the surface area of 3 football fields.Nanofilms or nanoplates have a thickness that’s nanosize, but their other two dimensions can be quite large. These nanoparticles can be designed into structures of a specific size, shape, chemical composition and surface design to create whatever is needed to do the job at hand. They can be suspended in liquid, ground into a powder, embedded into a composite or even added to a gas.
Many important functions of living organisms take place at the nanoscale. The human body uses natural nanoscale materials, such as proteins and other molecules, to control the body’s many systems and processes. A typical protein such as hemoglobin, which carries oxygen through the bloodstream, is 5 nms in diameter. Based on the definition of nanotech given above, biotech can be thought of as a subset of nanotech – “nature’s nanotechnology.”
Manipulating something so mind-bogglingly small is where the “technology” part comes in – it’s about trying to make technologies, such as computers and medical devices, out of these nanoscale structures. Nanotechnology is different from older technologies because unusual physical, chemical, and biological properties can emerge in materials at the nanoscale. Nano particles have different physical properties from their macro or life-size scale counterparts. For example, copper is an opaque mineral, but at the nano scale it is transparent. Some particles, like aluminum, are stable at macro scale but become combustible when reduced to nano-particles; a gold nanowire is twenty times stronger than a large bar of gold.
Molecular manufacturing is the name given to a specific type of “bottom-up” construction technology. As its name implies, molecular manufacturing will be achieved when we are able to build things from the molecule up, and we will be able to rearrange matter with atomic precision.
As I mentioned earlier, something so little understood is controversial, with many different points of view. These differences start with the very definition of nanotechnology, and moves on to what nanotechnology can achieve. Then there is the ethical challenge – what is the moral imperative about making technology that might help increase our lifespans available to all, for example?
Finally, the concern about possible health and environmental implications is perhaps the most controversial. The problem is that some properties of these tiny particles are unknown, and potentially harmful, and scientists are still trying to determine whether their size affects their toxicity. Scientists worry that the small particles used in nanotechnology could penetrate biological barriers designed to keep out larger particles; also we don’t have guidelines about how much we can safely ingest without harm. For more on possible harm to human health, click here.
Nanotechnology has been discovered by the textile industry – in fact, a new area has developed in the area of textile finishing called “Nanofinishing”. Making fabric with nano-sized particles creates many desirable properties in the fabrics without a significant increase in weight, thickness or stiffness, as was the case with previously used techniques. Nanofinishing techniques include: UV blocking, anti-microbial, bacterial and fungal, flame retardant, wrinkle resistant, anti-static, insect and/or water repellant and self-cleaning properties.
One of the most common ways to use nanotechnology in the textile industry is to create stain and water resistance. To do this, the fabrics are embedded with billions of tiny fibers, called “nanowhiskers” (think of the fuzz on a peach), which are waterproof and increase the density of the fabric. The Nanowhiskers can repel stains because they form a cushion of air around each cotton fiber. When something is spilled on the surface of the fabric, the miniature whiskers actually cohesively prop up the liquid drops, allowing the liquid drops to roll off. This treatment lasts, they say, for about 50 home wash cycles before its effectiveness is lost. A corollary finish is that of using nanoparticles to provide a “lotus plant” effect which causes dirt to rinse off easily, such as in the rain.
Nanotechnology can also be used in the opposite manner to increase the ability of textiles, particularly synthetics, to absorb dyes. Until now most polypropylenes have resisted dyeing, so they were deemed unsuitable for consumer goods like clothing, table cloths, or floor and window coverings. A new technique being developed is to add nanosized particles of dye friendly clay to raw polypropylene stock before it is extruded into fibres. The resultant composite material can absorb dyes without weakening the fabric.
The other main use of nanoparticles in textiles is that of using silver nanoparticles for antimicrobial, antibacterial effects, thereby eliminating odors in fabrics. Nanoparticles of silver are the most widely used form of nanotechnology in use today, says Todd Kuiken, PhD, research associate at the Project on Emerging Nanotechnologies (PEN). “Silver’s antimicrobial property is one that suits a lot of different products, and companies pretty much run the gamut of how many consumer products they put it in.”
PEN’s database of consumer products that contain nanoparticles lists 150 different articles of clothing, including athletic clothes, jogging outfits, camping clothing, bras, panties, socks, and gloves, that are treated with nano-silver because it kills the bacteria that cause odor.
The new research mentioned above was published in the American Chemical Society’s Nano Letters by researchers at Rice University , who found that the assumption that silver nanoparticles are toxic to bacteria is unfounded.
Scientists have long known that silver ions, which flow from nanoparticles when oxidized, are deadly to bacteria, and the assumption was made that silver nanoparticles were equally toxic. In fact, when the possibility of ionization is taken away from silver, the nanoparticles are practically benign in the presence of microbes, said Pedro Alvarez, George R. Brown Professor and chair of Rice’s Civil and Environmental Engineering Department. He said the straightforward answer to the decade-old question is that the insoluble silver nanoparticles do not kill cells by direct contact. But soluble ions, when activated via oxidation in the vicinity of bacteria, do the job nicely.
To figure that out, the researchers had to strip the particles of their powers. “Our original expectation was that the smaller a particle is, the greater the toxicity,” said Zongming Xiu, a Rice postdoctoral researcher and lead author of the paper. “We found the particles, even up to a concentration of 195 parts per million, were still not toxic to bacteria,” Xiu said. “But for the ionic silver, a concentration of about 15 parts per billion would kill all the bacteria present. That told us the particle is 7,665 times less toxic than the silver ions, indicating a negligible toxicity.” In fact, E. coli bacteria became stimulated by silver ions when they encountered doses too small to kill them.
The Environmental Protection Agency (EPA) granted it’s first-ever approval to use nanosilver particles in fabrics in December 2011, and is based on a conditional four year registration. . “Conditional” means that the manufacturer must provide test results (within four years) showing how the nanosilver particles interact with the environment. However, the EPA has a long history of letting such approvals linter, and has already expressed concern about nanosilver particles impacts on health, saying the approval “will likely lead to low levels of human and environmental exposure and risks.”
Last year, the Swiss Federal Laboratories for Materials Testing and Research examined what happens to silver nanoparticles in fabrics during washing – and found that these silver nanoparticles actually wash out of fabrics – so there is a high likelihood that the silver will spread into the environment. Another study found that socks treated with nanosilver lost, on average, half the nanoparticles embedded in the fabric during washing.
Among other well documented studies (see sites listed below) which have shown silver nanoparticles to be highly toxic to bacteria, fungi and other microorganisms is one by Duke University, in which it was found that silver nanoparticles negatively impacted the growth of plants – and also kills the beneficial soil microbes which sustain the plants. “Nanoparticles likely enter the environment through wastewater, where they accumulate in biosolids (sewage sludge) at wastewater treatment plants. One of the ways in which the sludge is disposed of is through land application, because it is valuable as a fertilizer. Whereas fertilizers add nutrients to the soil that are essential for plant growth, plants also depend on soil bacteria and fungi to help mine nutrients from the air and soil. Therefore, the antimicrobial effects of silver nanoparticles could have impacts at the ecosystem level—for example, affecting plants whose growth is dependent on soil-dwelling microorganisms.” Another study (Choi, Yu, Fernandez et al in Water Research 2010) found that once nanosilver is washed down the drain, it’s highly effective at killing the microorganisms used to treat sewage in wastewater treatment plants, which could lead to bigger problems with drinking-water safety.
The future for textile applications using nanotechnology is exploding due to various end uses like protective textiles for soldiers, medical textiles and smart textiles. Consider the T-shirt. Research is being done that will use nanotechnology-enhanced fabric so the T-shirt can monitor your heart rate and breathing, analyze your sweat and even cool you off on a hot summer’s day. What about a pillow that monitors your brain waves, or a solar-powered dress that can charge your ipod or MP4 player? The laboratory of Juan Hinestroza, assistant professor of Fiber Science and Apparel Design at Cornell University, has developed cotton threads that can conduct electric current as well as a metal wire can, yet remain light and comfortable enough to give a whole new meaning to multi-use garments. This technology works so well that simple knots in such specially treated thread can complete a circuit – and solar-powered dress with this technology literally woven into its fabric. Dr. Hinestroza designed the fabrics used in a Cornell Univesity fashion show by designer Olivia Ong, which guards the wearer against bacteria, repels stains, fights off allergies and oxidizes smog. And costs about $10,000 per yard to make.
And yet, there is mounting evidence that nanotechnology requires special attention. Here’s an excerpt from an interview with Andrew Maynard, science advisor to the Project on Emerging Technologies (PEN), from Technology Review:
- “Individual experiments have indicated that if you develop materials with a nanostructure, they do behave differently in the body and in the environment.
- We know from animal studies that very, very fine particles, particles with high surface area, lead to a greater inflammatory response than the same amount of larger particles. We also know that they can enter the lining of the lungs and get through to the blood and enter other organs. There is some evidence that nanoparticles can move into the brain along the olfactory nerve, so this is completely circumventing the blood-brain barrier.
- There really isn’t any consensus on how you go about evaluating the risks associated with carbon nanotubes yet. In cell cultures, you have to have some idea what kind of response you’re looking for. We already know in some studies that the lungs see carbon nanotubes almost as biological materials–they don’t see it as a foreign material. But then because of that, they start building up layers of collagen and cells around these nanotubes. They almost see them as a framework for building tissue on. Now, that actually may be a good thing in parts of the body, but in the lungs you end up using up the air space. But without that information, you wouldn’t necessarily know what were the appropriate cell tests to do in the first place.
- The thing that concerns me is, there is very much a mind-set that is based on the conventional understanding of chemicals. But nanomaterials are not chemicals. They have a structural component there as well as a chemical component.
At the recent meeting of the Society of Environmental Toxicology and Chemistry (SETAC), more than 20 studies were presented on the fate of nanoparticles once they enter the environment, and nearly all found that these materials were building up in organisms, such as earthworms, insects, and fish, and having subtle effects on their abilities to survive
The Rodale website had some suggestions for those of us who are worried about smelly clothes: Try nature and a little common sense.
- Pretreat. Before you wash your smelly gym clothes, sprinkle some baking soda on them, leaving it on for about an hour before laundering them to remove perspiration odors as well as stains.
- Launder with care. Because sweat can be oily, it can build up on clothing, becoming difficult to remove with regular detergents and water. Add a cup of white vinegar to the rinse cycle; vinegar helps break through oils on fabric, and it serves as a deodorizer. Or hand-wash your clothes with shampoo, which is designed to cut through body oils.
- Line-dry. Nothing cuts through bad odors like oxygen and sunlight. Let your clothes dry outside, rather than in a machine, and you’ll save energy, make your clothes last longer, and prevent offensive odors the next time you hit the gym. Read our Nickel Pincher’s line-drying story for the ultimate in line-drying advice.
Some other studies on toxicity of nanoparticles: