The Amazing Power of Cactus
Its gooey material can be engineered to purify water. But that’s just the beginning.
By Rosemarie D. Wesson with Sylvia W. Thomas
Nature is a very big part of emerging engineering research – and not just in developing technologies that imitate nature. Researchers are also including nature – that is, naturally occurring materials – in the engineering of useful solutions to human challenges. An example is the work currently being performed by a research team at the University of South Florida that exploits material in the cactus plant to purify water.
A cactus plant has a viscous, liquid material inside often referred to as cactus mucilage. This gooey substance is made of carbohydrates and sugars and is what allows the plant the ability to store water. Previous research has shown that pure mucilage is amazing in its ability to clean water, including removing arsenic, bacteria, and cloudiness from rural drinking water. Its potential uses include cleansing drinking water of cholera bacteria, cleanup following oil spills, and purifying groundwater in regions that see significant heavy metals contamination.
The engineering challenge now is to apply this knowledge in developing workable water filtration systems. Can you imagine engineers creating a form of natural cactus mucilage that can be used in homes and businesses? Can this natural material change the number of children and families we can save from dehydration, starvation, and disease, just by making the water we use and consume cleaner?
With funding from the National Science Foundation, engineers in USF’s Advanced Materials Bio and Integration Research Laboratory are spinning naturally occurring cactus mucilage into nanofibers. These spiderweb-like nanofibers are then layered to produce membranes.
Cactus mucilage can be mixed with different types of polymers to form nanofiber membranes using an electrospinning or force-spinning process, similar to making layers of cotton candy. Electrospinning is a process in which the surface tension of the polymeric cactus mucilage solution is influenced by an electric field and then undergoes plastic stretching to form fibers. The polymeric cactus mucilage solution forms a cone at the tip of a syringe needle, and a jet of fibers collects on a plate as a non-woven web. The nanofibers are gathered in spiral manner with fiber diameters ranging from nanometers to a few microns. These polymeric cactus membranes are made of nontoxic, biodegradable, and inexpensive materials.
Cactus mucilage has been electrospun with polyvinyl alcohol and polystyrene polymer solutions to make hydrophilic nanofiber membrane filters. Typically these polymer fibers are hydrohobic, repelling water. However, with the incorporation of the natural cactus mucilage, the fibers are hydrophilic and attract water. As a result, cactus nanofiber membranes can be used as water filters to remove arsenic content and other impurities from water.
Effective water treatment using cactus mucilage could help address a major and growing global problem. Fresh water, one of the most essential needs for human life, is only available to 1 out of every 12 people in the world, and only 1 percent of this fresh water is safe for drinking. The World Health Organization has mandated that research be conducted to reduce this 1:12 ratio of people currently living without clean drinking water and experiencing the burden of disease.
This is just the beginning. Further investigations are under way to use these cactus nanofiber membranes for toxic sensing, wound healing, and tissue scaffolding to further explore the natural capability of the cactus.
Rosemarie D. Wesson, Ph.D., P.E., is a program director in the National Science Foundation’s Directorate for Engineering and an adjunct professor of chemical engineering at the University of Maryland, College Park. Sylvia W. Thomas, Ph.D., is an assistant professor in electrical engineering and a member of the Advanced Materials Bio and Integration Research (AMBIR) Laboratory at the University of South Florida.