Johns Hopkins, had established that some viruses are able to make their way through the human mucus barrier. Hanes and his colleagues decided to look for a chemical coating that might mimic the characteristics of a virus.
"We found that the viruses that got through had surfaces that were attracted to water, and they had a net neutral electrical charge," said Samuel K. Lai, a Johns Hopkins chemical and biomolecular engineering doctoral student from Canada and Hong Kong who was lead author of the journal article. "We thought that if we could coat a drug-delivery nanoparticle with a chemical that had these characteristics, it might not get stuck in the mucus barrier."
To make their nanoparticles behave like viruses, the researchers coated them with polyethylene glycol, PEG, a non-toxic material commonly used in pharmaceuticals. PEG dissolves in water and is excreted harmlessly by the kidneys.
The researchers also considered the size of their nanoparticles. Previous studies indicated that even if nanoparticles did not stick to the mucus, they might have to be smaller than 55 nanometers wide to pass through the tiny openings in the human mucus mesh. (A human hair is roughly 80,000 nanometers wide.) Using high-resolution video microscopy and computer software, the researchers discovered that their PEG-coated 200-nanometer particles could slip through a barrier of human mucus.
They then conducted further tests to see how large their microscopic drug carriers could be before they got trapped in the mesh. Larger nanoparticles are more desirable because they can release greater amounts of medicine over a longer period of time. "We wanted to make the particles as large as possible," said Hanes, who also serves as director of therapeutics for the Institute for NanoBioTechnology at Johns Hopkins. "The shocking thing was how fast the particles that were 500 nanometers wide moved through the mucus mesh. The work suggests that the openings
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Source:Johns Hopkins University
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