Research Stories

by Melissa Crytzer Fry

Are nanomaterials really a big deal to humans? That's what ASU life sciences professor David Capco and his graduate research assistant Brian Koeneman want to know.

Capco and Koeneman work with ASU environmental engineer Paul Westerhoff. They all want to better understand the toxicity of nanomaterials in humans. As a first step, the researchers developed a filter membrane system that mimics the small intestine.

The scientists add titanium dioxide nanoparticles into the top chamber of the cell culture system. Once inside the system, the nanoparticles come in contact with a layer of intestinal cells—much like they would if a person ingested nanomaterials in water.

The bottom chamber of the model represents where the body's bloodstream would be located. It also mimics a supportive cell tissue called the extracellular matrix. Using the chamber, the ASU team can precisely measure how many nanoparticles penetrate the epithelial cell lining and how many could enter the blood.

The studies have revealed that the titanium is actually passing through the cell lining and into the bloodstream at rates of two to 14 percent. "The cell did seem to stop a majority of the particles," explains Koeneman.

But at what level are titanium nanoparticles toxic to the human body? The scientists first had to know what to look for to determine if something is toxic or not.

"We increased the nanoparticle concentration to a higher level than you would probably ingest," Koeneman adds. "We needed to know what types of responses we should be looking for."

They found increased amounts of calcium in the cells and a shortening of the intestine's hair-like structures, known as villi. These structures increase the surface area of the intestine and allow for absorption of nutrients.

"When the villi are decreased, the area of the cell is decreased. This means the body's ability to absorb nutrients is affected," Koeneman says. Even though the titanium did not kill the cells, the researchers wanted to see if any other effects were occurring.

They used a powerful electron microscope to study the gaps between the cells. These gaps are called junctional complexes. The gaps illustrate how tight the intestinal membrane is sealed.

"The lining leaks as it is degraded. More nanomaterials make it through," says Westerhoff. The ASU team found that prolonged exposure to nanoparticles does appear to degrade the cell lining.

The scientists also recorded a toxic response with the study of quantum dots. Quantum dots are human-built nanostructures. They are being developed as a method for targeted drug delivery within the human body.

"The metal cadmium core quantum dots killed the cells," says Koeneman. Just one milligram of quantum dot nanomaterial, when introduced to one liter of water, resulted in cell death.

"We now have a better understanding of the effects nanoparticles have on human cells," says Capco. "We can start to investigate newly designed nanomaterials with our novel method."

The resulting speed and cost savings will allow scientists to conduct toxicity studies that can keep up with the development of new nanomaterials.

"We also need to continue educating the public," Koeneman adds. "We need to make sure there is no backlash that shuts down future valuable nanotechnology research."

Read more about the environmental impact of nanoparticles in "Too small to see."