Stable and robust polymer nanotubes stretched from polymersomes
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Communicated by William D. Phillips, National Institute of Standards and Technology, Gaithersburg, MD, December 14, 2005 (received for review August 15, 2005)
Abstract
We create long polymer nanotubes by directly pulling on the membrane of polymersomes using either optical tweezers or a micropipette. The polymersomes are composed of amphiphilic diblock copolymers, and the nanotubes formed have an aqueous core connected to the aqueous interior of the polymersome. We stabilize the pulled nanotubes by subsequent chemical cross-linking. The cross-linked nanotubes are extremely robust and can be moved to another medium for use elsewhere. We demonstrate the ability to form networks of polymer nanotubes and polymersomes by optical manipulation. The aqueous core of the polymer nanotubes together with their robust character makes them interesting candidates for nanofluidics and other applications in biotechnology.
Footnotes
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↵ ‡ To whom correspondences should be addressed. E-mail: kristian{at}nist.gov.
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↵ * Present address: NASA Langley Research Center, Hampton, VA 23681-2199.
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↵ † Present address: Gettysburg College, Gettysburg, PA 17325.
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Author contributions: K.H. designed research; J.E.R., J.M.W., R.B.K., and C.P. performed research; J.E.R., J.M.W., R.B.K., C.P., and K.H. contributed new reagents/analytic tools; J.E.R., R.B.K., and K.H. analyzed data; and J.E.R., J.M.W., R.B.K., and K.H. wrote the paper.
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Conflict of interest statement: No conflicts declared.
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Abbreviation: TEM, transmission EM.
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↵ § The experiment of ref. 20 found that the intermonolayer friction of a polymersome membrane of a particular formulation was ≈1 order of magnitude higher than that of a typical phospholipid membrane. That is, the force required to pull a nanotube from their polymer membrane is ≈1 order of magnitude higher than the force required to pull a nanotube from a typical phospholipid membrane.
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↵ ¶ We typically pulled nanotubes from giant polymersomes with diameters of >5 μm, because these polymersomes adhered more readily to the coverslip surface and therefore did not move as we pulled on the membrane.
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↵ ∥ The corrugation also can be seen under fluorescence microscopy with nanotubes containing the membrane dye DiO-C16 and appears only after the addition of the cross-linking reagents. When care is taken to ensure that both ends of the nanotube are held securely and the nanotube is under some tension, the fraction of nanotubes that are corrugated, as measured with fluorescence microscopy, can be <10%.
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↵ ** We obtain a membrane thickness of 8 nm for our polymers using the curve in figure 3 of ref. 27. This value is consistent with measurements based on our TEM images (circled region of figure 3), which appear to give a membrane thickness of ≈12 nm but systematically overestimate the actual value because the images are not true cross-sectional views.
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Freely available online through the PNAS open access option.
