Shaping Particles The Easy Way

Whether it's round, wrinkled, or rectangular, a polymeric particle's shape can strongly influence its properties. But there's been no simple way to control these shapes, until now.

Researchers at the University of California, Santa Barbara, have developed a versatile and inexpensive method for making substantial quantities of polymeric particles in more than 20 shapes and sizes (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.0705326104). The advance could impact applications in drug delivery and personal care, where polymeric particles are important tools.

"Shape affects nearly every function of particles," says Samir Mitragotri, who spearheaded the project with Julie A. Champion and Yogesh K. Katare. "For example, in drug delivery, polymeric particles are used to encapsulate drugs and release them over prolonged periods of time or target them to specific tissues. Shape influences how drug-carrying particles circulate in blood and adhere to their target, how particles are cleared by the immune system, and the rate of drug release."

To make the shapely particles, the researchers suspend spherical micro- or nanoscale polystyrene beads in polyvinyl alcohol (PVA) and cast the solution into films. Then, using solvent or heat, they liquefy the particles and stretch the films in either one or two dimensions, deforming the spheres into various shapes depending upon how the films are stretched.

Alternatively, the team stretches the polymer particle-PVA film to create voids around each sphere and then liquefies the particles so they fill the empty spaces. After resolidifying the polystyrene, the researchers dissolve the surrounding PVA and collect the particles.

"Our method is not only versatile in terms of the shapes that it can produce, but it is also easy to use and employs routine laboratory methods and equipment," Mitragotri says.

"This is very exciting work based on a powerful concept," comments University of Michigan engineering professor Joerg Lahann. He adds that the technique's impressive control of shape and size is likely to be useful for a range of applications, particularly in drug delivery and personal care.