By Kelly A. Reynolds, MSPH, PhD

Search the term nanosponge in scientific databases and you’ll find a handful of articles on their use to deliver chemicals (i.e., drugs, medications, oxygen) to sites within the human body. Primarily explored as a drug delivery system for cancer tumor treatments, new applications are emerging. These invisible particles have many beneficial uses in clinical sciences, soaking up the bad stuff (i.e., toxins and bacteria) and supplying the good stuff (i.e., medicine) within the body. Nanotechnology is rapidly growing with uses in the fields of physics, chemistry, material science, engineering and environmental science. While some are concerned that the thousands of tons of produced nanomaterials could be potent environmental pollutants, others are tapping into the benefits of these tiny powerhouses to reduce pollutants in the body and the environment, including water treatment.


One big advantage to these nanosponges is that they are capable of absorbing different toxins. In other words, treatments do not have to be tailored to a specific agent; rather, the broad spectrum sponges will capture and neutralize hazards from a wide range of sources.


What are nanoparticles?
Nanomaterials, in particular nanoparticles, have been recognized as byproducts of material manufacturing for decades and have been used in the manufacturing of certain products (i.e, carbon black filler in tires). A variety of newer technologies has evolved since, which greatly improved the production and commercialization of nanoparticles. Measuring equal to or less than 100 nanometers, materials formulated as nanoparticles tend to be more reactive than their parent material due to the increased surface area per unit weight. (The website understandingnano.com provides a list of their applications, particularly in medicine.) Medical uses include: starving cancer cells by blocking access to nutrient-rich cells; delivery of encapsulated chemotherapeutic drugs or antiviral medications (now being tested on the incurable human immunodeficiency virus) and delivery of disease-fighting antigens to boost the immune system.

Nanosensors are also developed for diagnostics. The idea is that nanoparticles with attached beacons (actually biochemical amino acids, or the building blocks of proteins) can act as biomarkers of disease. Long ago, scientists learned to mimic competitive binding between cells. What this means is that nanoparticles with their signal beacons can be designed to attach to cancer cells, which in turn causes the release of the beacons; therefore, detection of released beacons indicates the presence of cancer at a very early stage. Other healthcare-related applications are the use of nanoparticles to treat fabrics. Adding tiny metal particles to clothing naturally inhibits bacterial persistence and growth. Nurses’ scrubs are sometimes impregnated with microscopic silver particles to reduce the transmission of germs between patients. Aluminosilicate nanoparticles have been added to medical bandages to help blood clot faster in open wounds.

Soaking up toxins
Diagnostics, drug delivery, inhibition of bacteria: these are all common uses of nanoparticles. A recent publication in Nature Nanotechnology (April, 2013) boasts a new application: the nanosponge. As the name suggests, nanosponges are designed to sop up toxins from the environment, which in this case, happens to be the human bloodstream. Toxins produced by bacteria, such as Methicillin-resistant Staphylococcus aureus (MRSA) and the deadly E. coli, as well as venomous snakes and even bees, are not able to persist in the blood when inoculated with nanosponges. So far, studies have only been conducted in mice but with great success. In one set of experiments, 89 percent of mice exposed to lethal levels of toxin from MRSA bacteria survived when pre-innoculated with the sponges. One big advantage to these nanosponges is that they are capable of absorbing different toxins. In other words, treatments do not have to be tailored to a specific agent; rather, the broad spectrum sponges will capture and neutralize hazards from a wide range of sources. In another clever advancement, nanosponges packaged inside red blood-cell membranes enables them to remain incognito to the human immune system while also luring toxins that target red blood cells to destroy. What the toxin encounters is a Trojan Horse of absorptive nanoparticles inside the cell. Next on the agenda for researchers is to translate their research from mice to humans.


Removal of waterborne contaminants via nanosponges may not be any more effective compared to current treatment technologies (i.e., activated carbon and resin fillers) but researchers are confident that improvements in the technology will eventually surpass conventional treatments.


Water quality and human health
Nanosponges were originally engineered in the US over 10 years ago at the Los Alamos National Laboratory. The tiny particles are well-suited to remove contaminants from passing water and can be engineered as sensors, as well as sorbents. Rice University and Penn State University researchers found that the addition of boron in the manufacture of carbon nanotubes produced a robust floating sponge that could be used to soak up environmental oil spills. Additives such as iron can actually transform waterborne contaminants to less toxic forms in the treatment process. These varied applications have earned nanosponges the label of smart filters. Removal of waterborne contaminants via nanosponges may not be any more effective compared to current treatment technologies (i.e., activated carbon and resin filters) but researchers are confident that improvements in the technology will eventually surpass conventional treatments. Current limitations are the cost to manufacture nanoparticles. In addition, the nanosponges may be too efficient at removing compounds from water; stripping drinking water of essential nutrients and minerals may be an unintended consequence. Perhaps the greatest concern with the nanoparticle explosion is that we do not know much about the public health risks associated with their use, or the environmental health risks. Due to their small size, nanoparticles may be easily inhaled and deposit deep in the lungs. Similarly, particles can be absorbed in the gut and transported to other organ systems in the body. Understanding potential routes of exposure and possible adverse health effects is critical prior to scaling up the use of nanoparticles to treat drinking water.

Conclusions
Nanotechnology is poised to take over with varied applications in clinical applications, water treatment and a long list of other potential benefits. Few studies have focused on the exposure assessment and potential human health risks associated with increased nanoparticle use. Such studies should be as much of a priority as the technology development itself.

References

  1. Raab, C.; Simko, M.; Fiedeler, U.; Nentwich, M. and Gazso, A. Production of nanoparticles and nanomaterials, February 2011. [Online]. Available: http://epub.oeaw.ac.at/ita/nanotrust-dossiers/dossier006en.pdf. [Accessed 10-05-2013].
  2. Boyson, E. Nanoparticles: Uses and Applications, Hawk’s Perch Technical Writing, LLC, 2013. [Online]. Available: www.understandingnano.com/nanoparticles.html. [Accessed 09 05 2013].
  3. Hu, C.J.; Fang, R.H.; Copp, J.; Luk, B.T.; Zhang, L. “A biomimetic nanosponge that absorbs pore-forming toxins,” Nature Nanotechnology, vol. 8, pp. 336-340, 2013.
  4. Makoni, M. “Nanosponges: South Africa’s High Hopes for Clean Water,” The Science and Development Network, 6 May 2009. [Online]. Available: www.scidev.net/en/features/nanosponges-south-africa-s-high-hopes-forclean-wa.html. [Accessed 13 May 2013].
  5. Hashim, D.P.; Narayanan, N.T.; Romo-Herrera, J.M. et al. “Covalently bonded three-dimensional carbon nanotube solids via boron induced nanojunctions,” Scientific Reports, vol. Article number 363, no. April, 2012.
  6. Hoet, P.H.M.; Bruske-Hohlfeld, I. and Salata, O.V. “Nanoparticlesknown and unknown health risks,” Journal of Nanobiotechnology, vol. 2, no. 12, 2004.

About the author
Dr. Kelly A. Reynolds is an Associate Professor at the University of Arizona College of Public Health. She holds a Master of Science Degree in public health (MSPH) from the University of South Florida and a doctorate in microbiology from the University of Arizona. Reynolds is WC&P’s Public Health Editor and a former member of the Technical Review Committee. She can be reached via email at reynolds@u.arizona.edu

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