Using this technique, the team created cylindrical shapes of various dimensions, suspending the structures in liquid to observe how they transformed. All cylinders morphed into wavy, star-shaped structures, but with characteristic differences: Short, wide cylinders evolved into structures with more wrinkles, whereas tall, slender cylinders transformed into less wrinkly shapes.
Fang concluded that as a hydrogel expands in liquid, various forces act to determine its final shape.
"This kind of tubular structure has two ways of deforming," Fang says. "One is that it can bend, and the other is that it can buckle, or squeeze. So these two modes actually compete with each other, and the height tells how stiff it is to bending, while the diameter tells how easy it is to stretch."
From their observations, the team drew up an analytical model representing the relationship between a structure's initial height, diameter and thickness and its ultimate shape. Fang says the model may help scientists design specific shapes for more efficient drug-delivery systems.
Fang says the group's results may also help explain how complex patterns are created in nature. He points to peppers whose cross-sections can vary widely in shape as a case in point: Small, spicy peppers tend to be triangular in cross-section, whereas larger bell peppers are more star-shaped and wavy. Fang speculates that what determines a pepper's shape, and its number of waves or wrinkles, is its height and diameter.
Fang says the same principle
|Contact: Caroline McCall|
Massachusetts Institute of Technology