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Nanomaterials

Background Information

Nanoscale materials are substances that have at least one dimension less than 100 nanometers. They possess unique optical, magnetic, or electrical properties. One example of these materials is ultrafine particulate matter—very fine, tiny particles of matter.

Nanoscale materials are engineered from nearly any substance. A few examples include:

  • Semiconductor nanocrystals (tiny light-emitting particles on the nanometer scale)
  • Organic dendrimers (repetitively branched molecules)
  • Carbon fullerenes ("Buckyballs"—molecules made up of 60 carbon atoms arranged in the shape of a sphere)
  • Carbon nanotubes (cylindrical carbon nanostructures)

Nanoscale materials have appeared in commerce as industrial and consumer products and as drug delivery formulations. In fact, the global demand for nanomaterials and devices is measured as being in the multi-trillions of dollars.

Commercial applications and resultant opportunities for human exposure may differ substantially for "nanoscale" compared with "bulk" materials. Surface properties are changed by coating nanoscale particles with different materials, but surface chemistry is also influenced by the size of the particle—making the impact of size an important factor. This interaction of surface area and particle composition in eliciting biological responses adds an extra dimension of complexity in evaluating potential adverse events that may result from exposure to these materials.

NTP Studies

NTP scientists are concerned with the potential toxicity of nanoscale materials, in particular, how and where these materials interact with the body, and what possible health concerns could result from the interaction. Current projects look at the size, shape, surface chemistry and composition of these materials.

Three core agencies that contribute to NTP—the National Center for Toxicological Research (NCTR), the National Institute for Occupational Safety and Health (NIOSH), and the National Institute of Environmental Health Sciences (NIEHS)—coordinate together to study several classes of nanoscale materials. Specific classes of nanoscale materials covered by NTP activities are:

List of Nanoscale Material Classes
Nanoscale Material Project
Carbon Fullerenes (Buckyballs)

NTP inhalation studies on fullerene C60 were conducted through an NIEHS testing contract. Two 13-week inhalation studies of fullerene C60 were completed. Additional studies of fullerene C60 have examined potential impacts on the immune system. These studies of rodent lungs involved two distinct particle sizes of C60 atmospheres. Studies examined:

  • Toxicity
  • Tissue distribution
  • Immunological effects
  • Clearance in the lungs

Fullerene C60 was evaluated under a NIOSH-NIEHS Interagency agreement to provide a better assessment of US worker exposures and occupational health concerns.

Carbon Nanotubes

The multiwalled carbon nanotubes (MWCNT) project examines the impact of nanotube length and diameter. Studies analyzed the toxicity of multiwalled carbon nanotubes in the lungs of animal models.

The initial phase of the project included the procurement and physical and chemical characterization of 24 commercially available carbon nanotubes to evaluate the diversity of commercially available materials. Results from this phase were used for selection of a specific test article for additional tests. Based on toxicity and clearance data, a 30-day study was designed to evaluate immunotoxicity at lower atmosphere concentrations. In addition, a chronic 2-year toxicity and carcinogenicity study in rats and mice exposed to these low concentrations of MWCNT is also ongoing.

Carbon nanotube exposure has been evaluated under a NIOSH-NIEHS Interagency agreement to provide a better assessment of US worker exposures and occupational health concerns.

Nanoscale Crystalline Cellulose

National Institute for Occupational Safety and Health (NIOSH) staff, supported by a NIOSH-NIEHS Interagency agreement, conducted in vitro physicochemical analyses of a variety of micro and nanocrystalline cellulose (NCC) to assess dissolution and durability. Based on the persistence of nanocrystalline silver, NTP is developing plans for future in vivo studies of nanocrystalline cellulose.

Carbonaceous Nanomaterials

As part of another interagency agreement with NIOSH, NTP is committed to an industry-wide exposure assessment as well as epidemiology studies of U.S. manufacturers of engineered carbonaceous nanomaterials (ECN). The information collected includes:

  • Nanomaterials produced (including characterization of size and shape)
  • Size of worker population by facility
  • Tonnage of materials used or produced
  • Workforce size
  • Status
Nanoscale Silver

The U.S. Food and Drug Administration nominated nanoscale silver (n-Ag) for study by the NTP based on two factors:

  • Increasing widespread use in drug, food, and cosmetic products
  • The general lack of data on the toxicology and pharmacokinetics of these materials

The n-Ag project was conducted by scientists at the National Center for Toxicological Research (NCTR). In vitro toxicity and toxicokinetic studies on the effect of particle size of nanosilver pharmacokinetics were completed. Subchronic, or short-term, 13-week studies on different sizes of n-Ag have also been completed.

Cadmium Selenide Based "Quantum Dots"

Staff at NCTR evaluated the kinetics of tissue distribution following intradermal injection of quantum dots.

Scientists also evaluated kinetics and tissue distribution after dermal exposure of quantum dots to intact and dermabraded mice. Results showed that absorption of nanoscale materials through the skin depends on skin barrier quality, and that lack of an epidermis provides access to quantum dot penetration.

Metal Oxides
  • Titanium Dioxide

NTP studies on nanoscale titanium dioxide have been conducted as part of the nanotechnology safety initiative. One study, together with other FDA-supported studies, examined the tissue distribution of titanium dioxide materials in animal models following skin exposure. Results indicated that intact skin is an effective barrier to titanium dioxide nanoscale materials.

Studies also examined the resulting protein expression in the lymph nodes of mice following titanium dioxide exposure.

Titanium dioxide was evaluated at NCTR supported by a NCTR-NIEHS Interagency agreement.

Informational Resources

Resources From Other Organizations

Informational resources on topics related to nanoscale materials and nanotechnologies are listed below.

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