SPECIAL FEATURE: EMERGING TECHNOLOGIES
Researchers have discovered how to make synthetic polymer molecules form into long cylinders, a nanostructure potentially suited for drug-delivery applications.
Block copolymers can be found in rubber soles for shoes, and, more recently, in portable memory sticks (flash drives) for computers. Soon, the material might be found in the human body as well. Researchers have discovered how to make synthetic polymer molecules assemble and form into long cylinders, a nanostructure potentially suited for drug-delivery applications. The finding was first reported in the August issue of Science by a research team lead by Darrin Pochan, associate professor at the University of Delaware (Newark, DE), and Karen Wooley, professor at Washington University (St. Louis).
“A block copolymer is a long-chain molecule, a length of which, or block, is chemically different than the other,” says Pochan. “So, you put them in a solution where one of the blocks repels and tries to get away and the other doesn’t, which is how you get different shapes to form.”
The scientists used a tri-block copolymer composed of polyacrylic acid, polymethylacrylate, and polystyrene. They introduced it to a solution of tetrahydrofuran and water, as well as organic diamines. The technique relied on divalent organic counter ions and solvent mixtures to drive the organization of the block copolymers down specific pathways into long, one-dimensional structures.
In the past, self-assembly on the nanoscale has typically produced simple shapes, such as spheres, which present problems for drug delivery. “If you put little balls full of a drug into the bloodstream, the body’s organs and immune system will clear it out in a day,” Pochan says. “But, if you place the molecules into long, floppy cylinders, they may stay in the body for weeks.”
Floppy cylinder nanostructures can also be formed to provide multiple compartments (unlike a sphere, which is capable of providing only one compartment)—another potential advantage for drug delivery. Multicompartmental structures suggest intriguing possibilities, says Pochan, including devices that could store different drugs in separate compartments, thereby enabling a single device to deliver an entire drug regimen.
In addition to new shapes, the research has also yielded a bottom-up approach for building nanostructures. “Bottom-up manufacturing has gotten a bad rap in recent years, but this research has made it relevant for nanomanufacturing,” Pochan says. “Rather than design a large structure or component and use lithography to form it into what you want, our goal is to design a molecule with all the information it needs built-in, and then you throw it in water and it zips up into the desired complex shape and size.”
“It’s all about constructing materials and nanostructures in an easy way,” he adds.
University of Delaware, Newark, DE
Washington University, St. Louis, MO