Nano-style sheets may aid health, shield ecosystem

Microscopically, “nanomembrane” sheets made from nylon resemble a tangled web. The tiny iron oxide particles on the fiber surfaces can help clean toxic chemicals from water, but if the particles get separated from the web, they can become hazards themselves. In a new study, Cornell researchers examined these special nylon sheets – replete with applied nanoscale iron oxide particles – to see if the particles wash loose. The particles work like magnets to capture bacteria and viruses, and to extract chemicals or dye molecules out of water. Membranes with these particles attached could be used in devices to detect water contamination or in filters to remove chemicals or dyes from industrial waste. However, to be effective and safe, the particles need to stay on the membrane. The study evaluated the nanoparticle treatment uniformity and particle retention of the nylon membranes as they were processed (or washed) in solutions of varying pH levels. “It’s critical to evaluate particle retention and stability on fibers to reduce human health and environmental concerns,” said Nidia Trejo, a Cornell doctoral student in the field of fiber science. Trejo, who with Margaret Frey, professor of fiber science, authored the study, “A comparative study on electrosprayed, layer-by-layer, and chemically grafted nanomembranes loaded with iron oxide nanoparticles,” in the ("A comparative study on electrosprayed, layer-by-layer, and chemically grafted nanomembranes loaded with iron oxide nanoparticles") nanofibers Under a microscope, Nylon-6 fibers comprise nanomembrane sheets. The nanomembrane sheet structure looks like a dryer sheet but is made from layers of tiny, randomly oriented fibers that only can be seen with electron microscopes. These nanomembranes have a high surface-to-volume ratio, which enhances the material’s function. Manufacturing methods vary depending on the liquid environments in which the membranes would be used. Adhering nanoparticles of iron oxide to nylon fiber is done in three ways: electrospraying, which facilitates uniform nanoparticle placement in the fibers; layer-by-layer assembly, where particles are coated on the fiber electrostatically; or chemical bonding. “For the membrane, it’s important to evaluate particle retention and stability,” Trejo explained. “You would want the nanoparticles to stay on the Nylon 6 membranes so the material can have function throughout the life use. If the material is used for wastewater treatment applications, you wouldn’t want the particles themselves to become pollutants if are they releasing from the membranes and into the water.” A range of state-of-the-art facilities on campus was used by the researchers. The Cornell Center for Materials Research (funded through the National Science Foundation’s Materials Research Science and Engineering Center program) supported this study through its shared facilities. Additionally, Cornell’s Nanobiotechnology Center and the Cornell Nutrient Analysis Laboratory supported this research. Can nanofiber save your life? Researchers in professor Margaret Frey’s lab create fibers hundreds of times thinner than a human hair that can capture toxic chemicals and pathogens. The fibers have been designed and combined to prevent the spread of agricultural chemicals and to capture toxic substances in liquids. Tiny, complex devices traditionally are made in high-tech clean rooms using expensive equipment and costly material, like gold. Frey and her colleagues are replacing that cost by making the devices with nanofibers from plastics, outside the clean room, using an inexpensive, scalable process: electrospinning. Using nanofibers, processes done in a medical testing lab – for example, purifying samples, mixing ingredients, capturing bacteria – can be done with material about the size of a deck of cards. The fibers are a fast, easy and inexpensive way to concentrate on E. coli, cholera toxin or carcinogens and to improve accuracy of detection. Eventually, these fibers will be part of devices as inexpensive and easy to use as home pregnancy tests and will diagnose diseases without requiring specialized laboratories – particularly useful in regions with limited access to doctors and hospitals. To prevent pesticides from harming the environment, Frey and her students have encapsulated pesticides into biodegradable nanofibers. This keeps them intact until needed or makes sure they do not wash away from the plants they protect. The delivery system is created by electrospinning solutions of cellulose, the pesticide and polylactic acid – a polymer derived from corn. The materials are biodegradable and derived from renewable resources. “The chemical is protected, so it won’t degrade from being exposed to air and water,” Frey said, explaining that this keeps the chemical where it needs to be and allows it to time-release. “By allowing rapid detection of disease and preventing agricultural chemical release into the environment, these nanofibers just might save a life,” she said.
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A biodegradable nanogenerator made with DNA

Long-standing concerns about portable electronics include the devices' short battery life and their contribution to e-waste. One group of scientists is now working on a way to address both of these seeming unrelated issues at the same time. They report in the journal ("DNA-Assisted β-phase Nucleation and Alignment of Molecular Dipoles in PVDF Film: A Realization of Self-Poled Bioinspired Flexible Polymer Nanogenerator for Portable Electronic Devices") the development of a biodegradable nanogenerator made with DNA that can harvest the energy from everyday motion and turn it into electrical power. Lund Many people may not realize it, but the movements we often take for granted -- such as walking and tapping on our keyboards -- release energy that largely dissipates, unused. Several years ago, scientists figured out how to capture some of that energy and convert it into electricity so we might one day use it to power our mobile gadgetry. Achieving this would not only untether us from wall outlets, but it would also reduce our demand on fossil-fuel-based power sources. The first prototypes of these nanogenerators are currently being developed in laboratories around the world. And now, one group of scientists wants to add another feature to this technology: biodegradability. The researchers built a nanogenerator using a flexible, biocompatible polymer film made out of polyvinylidene fluoride, or PVDF. To improve the material's energy-harvesting ability, they added DNA, which has good electrical properties and is biocompatible and biodegradable. Their device was powered with gentle tapping, and it lit up 22 to 55 light-emitting diodes.
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Producing nanofibers with controlled size

Researchers studied the effective parameters on the production of polymeric nanofibers through electrospinning method ("Effect of electrospinning process parameters of polycaprolactone and nanohydroxyapatite nanocomposite nanofibers"). Nanofibers with desirable diameter and size can be produced using the results of this research by optimizing the process conditions. In this research, composite nanofibers of polycaprolactone/hydroxyapatite nanoparticles were produced through electrospinning method, and the effects of various process conditions were studied on the average diameter of the produced nanofibers. Results of this research can detect a range of variables that lead to the production of nanofibers at desirable size. Therefore, production costs reduce while the desirable nanofibers are produced faster. Effective parameters that affect the average diameter of the final nanofibers are polymer concentration, voltage and current of solution. The produced nanofibers can be used as three dimensional scaffolds in tissue engineering to cure and substitute damaged tissues, including bones. Tissues in human body are made of nanometric fibers. Therefore, scaffolds containing nanofibers produced through electrospinning method can be considered as appropriate environment for the growth of the cells. More textiles with waterproof and antibacterial properties can be produced by using these nanofibers in case other polymers are added to them. In addition, polymeric nanofibers can be used as filters and membranes in separation and purification industries.
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