February 21, 2006
Stretching Novel Polymer Nanotubes from Nanoparticles
Scientists at the National Institute of Standards and Technology (NIST) have created polymer nanotubes that are unusually long (about 1 centimeter) as well as stable enough to maintain their shape indefinitely. Described in a new paper in the Proceedings of the National Academy of Sciences USA, the polymer nanotubes may have use as channels in microfluidics and nanofluidics devices, or as nanoscale needles for injecting molecules directly into tumor cells.
While researchers have developed polymer nanotubes before, they have been fragile and usually collapse within a few hours. The NIST team, headed by Kristian Helmerson, Ph.D., developed processes for extending the shelf life of polymer nanotubes – considered essential for commercial applications – and forming sturdy nanotube network structures.
To realize these advances with polymer nanotubes, the researchers first made tiny, fluid-filled spherical containers consisting of polymers with one end that likes water and one end that does not. These fluid-filled containers are similar to liposomes, artificial cells with fatty membranes used in cosmetics and for drug delivery. The researchers made the membranes stretchy by adding a soap-like fluid to change the polymer membranes' mechanical properties. Then they used "optical tweezers" (highly focused infrared lasers) or tiny droppers called micropipettes to pull on the elastic membranes to form long, double-walled tubes that are less than 100 nanometers in diameter.
The investigators then added a chemical that breaks some of the chemical bonds present in one section of the polymers and induces new bonds to form between the two different sections, forming a rigid "cross-linked" membrane. The nanotubes are then snipped free from the parent cell with an "optical scalpel," a highly focused ultraviolet laser pulse. The nanotubes maintain their shape even after several weeks of storage, and can be removed from the liquid solution and placed on a dry surface or in a different container.
This work is detailed in a paper titled, “Stable and robust polymer nanotubes stretched from polymersomes.” The entire paper is available free of charge through PubMed Central.
This sequence of images taken at NIST shows the creation of a nanotube as a highly focused infrared laser tugs on a polymer membrane that has been colored with a fluorescent dye. The white scale bar indicates 10 micrometers.