Tracking Nano-Metal Marauders

Winter 2009

nanometalmaraudersOur bodies are constantly exposed to tiny invaders. Typically, the body’s natural first line of defense—the mucus barrier—traps and flushes these assailants out. But the mucus barrier may not always intercept everything it encounters, especially if that something is a nanoparticle the size of a handful of atoms.

Because of their unusual properties, many nanomaterials have become indispensable in consumer and industrial applications and medical products and devices. For example, nano-scale zinc oxide particles improve the coating ability of paint and the effectiveness of suntan lotion. But, if inhaled, metal oxides may trigger inflammation. Three Johns Hopkins researchers affiliated with the Institute for NanoBioTechnology—one from the Whiting School of Engineering and two from the Bloomberg School of Public Health—are studying the possibility that nanometal oxides slip through the mucus barrier into the lungs. And, if that happens, they want to know what kind of havoc these nanoparticles might wreak.

“What we learn from these particles may help us begin to understand the effect of other nanoparticles to which we all are exposed,” says principal investigator Shyam Biswal, associate professor in the Division of Toxicology at the Bloomberg School. He is joined by Engineering’s Justin Hanes, professor of chemical and biomolecular engineering, and Public Health’s Patrick Breysse, professor and director of the Division of Environmental Health Engineering. The team brings together expertise in exposure assessment, aerosol science, nanotechnology, the mucus barrier, and pulmonary molecular toxicology.

The researchers are seeking to answer several questions, notes Hanes. “Where these materials are being manufactured, are people exposed to nanometal oxides via inhalation? If so, would one expect one in 10 particles to get through the protective mucus barrier that lines the lung airways, or is it more like one in one trillion? What levels are acceptably low so as not to cause damage?” Hanes will trace the travel of metal oxide nanoparticles in samples of fresh, undiluted human mucus. and high-speed video, he will track and videotape particle motion, and measure and calculate diffusion using mean-square displacement equations. “This will give us an overall picture of how well specific particles can penetrate the mucus barrier over time,” he explains.

Biswal will examine how much inhaled nanometal oxide is required to trigger an inflammatory response in lung cells. And Breysse will analyze the moisture collected in the exhaled breath of people working in the closed environment of a nanometal oxide manufacturing facility. This data will establish parameters from which the team hopes to extrapolate how much the average person might be exposed to such nanoparticles in an open environment—such as walking down the street. “Exposure to nanomaterials in occupational settings is measurable, but exposure in non- occupational settings is hard to characterize,” says Biswal, who holds a joint appointment in the Department of Chemical and Biomolecular Engineering. “These studies will help us understand the health effects of nanoparticles that we might encounter every day.”