New research has revealed that large nanoparticles can penetrate mucus barriers and may therefore provide an efficient means of mucosal drug delivery (Lai SK et al. Proc Natl Acad Sci U S A. doi:10.1073/pnas.0608611104 [published online January 23, 2007]).
While nanoparticles that are 200 to 500 nm in diameter can encapsulate high concentrations of drugs and provide sustained delivery, it was previously thought that they were too large to diffuse through human mucus barriers. But scientists at Johns Hopkins University, in Baltimore, have now found that when such nanoparticles are coated with polyethylene glycol of certain molecular weights, they can penetrate samples of fresh human cervicovaginal mucus with an effective diffusion coefficient only 4- and 6-fold lower than that for the same particles in water. Smaller coated nanoparticles or larger ones not coated in polyethylene glycol were much less effective at mucus penetration. The work also suggests that the openings in the human mucus barrier are much larger than originally thought.
Hampton T. Nanoparticles and Mucus. JAMA. 2007;297(9):941. doi:10.1001/jama.297.9.941-b