New Shape-Shifting Materials Let Biomedical Implants Morph Over Time
Shape-shifting materials that can be programmed to morph over time could lead to medical implants that unfold at controlled rates inside the body, a new study finds.
Shape-shifting capabilities can enable a wide range of new applications and extend existing ones, according to the researchers. "Living organisms do it all the time," said study senior author Sergei Sheiko, a materials scientist at the University of North Carolina at Chapel Hill. "Birds change the shape of the wings to enable taking off and landing."
Scientists have developed many different shape-shifting materials over the years, but these usually required an external trigger in order for the structures to change form — for instance, the introduction of light, heat, electricity or acidity. In contrast, there are many situations in which researchers might want an item to change shape without the need for outside cues that could upset a stable environment. For example, "the human body makes a tremendous effort to maintain constant temperature and pH,
Sheiko and his colleagues have now developed materials that change shape not due to an outside trigger, but because of the passage of time. "This is similar to a coffeemaker or washing machine — you dial the timer and let it run," he said.
These materials possess two networks of chemical bonds, which serve as counteracting forces. One network is elastic, holding the energy that drives the shape-shifting process, while the other network can flow, controlling how quickly a material reaches its final shape. By varying the concentrations of these bonds, the researchers can program the rate at which shape shifting takes place, lasting anywhere from seconds to hours.
In experiments, the scientists were able to create an artificial blooming flower with petals that gradually opened, one by one. "The general motivation behind this work was to endow synthetic materials with functions and properties of living tissues," Sheiko said.
Temperature can speed up or slow down these clocks. This is "an additional opportunity to control the process," Sheiko said. "This might be useful for certain applications."
Shape-shifting materials that can change shape over time could spur the development of "biomedical implants that can be programmed to alter [their] shape after insertion into the body," Sheiko said. While the initial shape can favor noninvasive or minimally invasive surgery, the final shape can expand to fit an implant's final desired form, he said.
Future research could explore how to encode a delay prior to shape shifting, Sheiko said. "Programming a sequence of multiple shapes is another challenge," he added.