Los Angeles, CA, USA. A new review article examines measures to enable safe design of nanomaterials. Their expanded development with enhanced performance characteristics for use in commercial and medical applications has increased the likelihood of people coming into direct contact, with uncertain effects on human health.

The materials can be reduced to fibers smaller than a one tenth of a micrometre in at least one dimension and can probe the human body and diagnose medical conditions that would be overlooked by more traditional methods. Nanomaterials also have direct applications in more precise and strengthed surgical instruments and implants.

There are currently more than 800 products on the market — including clothes, skin lotions and cleaning products — claiming to have at least one nanocomponent, and therapeutic nanocarriers have been designed for targeted drug delivery inside the human body. Human exposure to nanomaterials, which are smaller than one one-thousandth the diameter of a human hair, raises some important questions, including whether these "nano-bio" interactions could have adverse health effects.

 

Nanotechnology & Nanotubes

 

Nanotechnology manipulates matter on an atomic or molecular scale. Nanotubes are tiny structures with unique electronic, thermal, and structural properties.

 

Diverse applications range from novel extensions of conventional device physics to completely new approaches based upon molecular self-assembly, to developing new materials with nanoscale dimensions, even to speculation on whether we can directly control larger assemblies of matter on the atomic scale.

 

This makes the technology potentially useful for biomedicine, electronics, optics and other fields that depend on the use of advanced materials.

 

Products based on nanotechnonology (nanotech) are increasingly present in everyday life. Currently, there are more than a thousand products that range from solar panels, scratch-resistant automobile paint to enhanced golf clubs.

 

The first use of the concepts involved (predating the term nano-technology) came in a talk by physicist Richard Feynman at a Caltech meeting of the American Physical Society: There's Plenty of Room at the Bottom (29 December 1959). [ Download PDF ] 

 

Feynman described a process by which the ability to manipulate individual atoms and molecules might be developed, using one set of precise tools to build and operate another proportionally smaller set, so on down to the needed scale. Currently, there are two main approaches:

 

• Bottom-up. Materials and devices are built from molecular components which assemble themselves chemically by principles of molecular recognition.

 

• Top-down. Nano-objects are constructed from larger entities without atomic-level control.

 

This is work on a very small scale. One nanometer (nm) is one billionth of a meter (10-9), or 3.93700787402E-8 inches. It equals ten Ångström. The proportion of a nanometer to a meter is the same as that of a marble to the size of the earth. By comparison, typical carbon-carbon bond lengths (the spacing between atoms in a molecule) range from 0.12—0.15 nm.

 

The diameter of a DNA double-helix is around 2 nm. Even the smallest cellular lifeforms, such as the bacteria of the genus Mycoplasma have dometers around 200 nm in length.

 

New studies of nanotechnology and its reception by the public indicate the influences of cultural and religious beliefs on the technology's acceptibility. This can be distinguished from a lack of confidence in manufacturing technique; such errors have been detected, but are susceptible to regulatory correction.

 

Cultural and religious impediments are a different matter — they require more extensive educational intervention.

 

The image above is a view from within a flattened, twisted carbon nanotube. Courtesy of Vin Crespi, Pennsylvania State Physics. Distributed under the Creative Commons license v2.0.

"Instead of waiting for knowledge to unfold randomly, we can already begin to view the events at nano-bio interface as a discoverable scientific platform that can be used for setting up a deliberate inorganic-organic roadmap to new, better and safer products."

— Andre NelIn a research review published in the journal Nature Materials, the team provides a comprehensive overview of current knowledge on the physical and chemical properties of nanomaterials that allow them to undergo interactions with biological molecules and bioprocesses.

Despite remarkable advances in nanoscience, relatively little is known about the intracellular activity and function of engineered nanomaterials, an area of study particularly important for the development of effective and safe nanoparticle drug-delivery systems.

Much of the current knowledge derives from the study of tagged or labeled nanoparticles and their effects on cells after cellular uptake — without any detailed understanding of what these interactions may lead to, good or bad.

The review article examines the variety of ways in which nanomaterials interface with biological systems and presents a roadmap of the physical and chemical properties of the materials that could lead to potentially hazardous or advantageous interactions at the nano-bio interface. A better understanding of the biological impact, combined with appropriate stewardship, will allow for more informed decisions about design features for the safe use of nanotechnology.

"What we have established here is a blueprint that will serve to educate the first generation of nanobiologists," said Dr. Andre Nel, leader of the team and chief of the division of nanomedicine at the David Geffen School of Medicine at UCLA and the California NanoSystems Institute.

"Based on our rapidly improving understanding of nano-bio interactions, we have done a thorough examination of the literature and our own research progress to identify measures that could be taken for safe design of nanomaterials," he said.

"Not only will this improve the implementation and acceptance of this technology, but it will also provide the cornerstone of developing new and improved nanoscale therapeutic devices, such as drug-delivering nanoparticles."

"We are committed to ensuring that nanotechnology is introduced and implemented in a responsible and safe manner," said Nel. The review article spotlighted several important research advancements:

• A classification of the interactions when nanomaterials contact and bind to biological systems will help scientists understand how man-made materials may react when exposed to cells, tissues and various life forms in different natural environmental contexts.
  
  
• When nanomaterials enter a biological fluid — for example, blood, plasma or interstitial fluid — the materials' surface may be coated with proteins.
  
  Understanding how these protein layers change the properties of the nanomaterials and the ways in which they interact in the body can provide valuable information on how to alter the protein coatings to allow for targeted delivery of nanomaterials to specific tissues, such as in cancer treatments.
  
  
• Physicochemical properties such as size, charge, shape and other characteristics could greatly affect the ability of nanomaterials to enter a cell; this could determine whether a material can be useful in nanomedicine applications or could cause harm if taken in by life forms in an ecosystem or food chain.
  
  
• Nanoparticles can elicit a wide range of intracellular responses, depending on their properties, concentrations and interactions with biological molecules. These properties and their relationships to cellular function can induce cellular damage or induce advantageous cellular responses, such as increased energy production and growth.

Based on the link between certain nanomaterial properties and potential toxic effects, the team asserts that scientists can reengineer specific nanomaterial properties that are hazardous while maintaining catalytically useful function for industrial use.

As an example of a safe design feature, some nanoparticles now receive a surface coating designed to improve safety by preventing bioreactivity. Nanoparticles in cosmetic formulations such as suntan lotions, for instance, may be coated with a water-repelling polymer to reduce direct contact with human skin.

An extension of this principle uses polymers and detergents to decrease cellular uptake. However, there is the potential that when the coating wears off, the material may become hazardous. It is therefore important to consider improving the stability of coating substances. Coating nanoparticles with protective shells is also an effective means of preventing the breakup of materials that could release toxic substances upon dissolution.

"Instead of waiting for knowledge to unfold randomly, we can already begin to view the events at nano-bio interface as a discoverable scientific platform that can be used for setting up a deliberate inorganic-organic roadmap to new, better and safer products," Nel said. "What we can identify by understanding the rules that shape the nano-bio interface will have a massive impact on the ability to develop safe nanomaterials in the future."

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Interactions Between Nanomaterials and Biosystems
Monday, 29 June 2009

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