Flowers usually open to the sun, but scientists at the University of North Carolina at Chapel Hill have engineered a polymer bloom that unfurls over the course of two hours, due to the location, strength and number of its molecular bonds. This feat of hydrogel horticulture isn’t just aesthetically pleasing, it also demonstrates how a material can be programmed to change shape over hours and minutes, without an external trigger.
Covalent vs. Physical Crosslinks
The UNC team based their smart material on a soft polymer with the texture of human cartilage. The majority of bonds are reversible physical crosslinks which are easily broken and give the polymer its flexibility. A small portion of the polymer’s molecular bonds are covalent crosslinks, which enable the material to return to its original shape after being stretched, like a rubber band. The UNC team adjusted the molecular structure of their polymer so the physical crosslinks would act as a brake against shape recovery by the covalent crosslinks, allowing control of the rate of shape change.
Biomedical Applications of Shape-Changing Polymers
The ability of smart materials to change shape and function without an outside trigger has many potential biomedical applications, including slow-release drug delivery and minimally invasive surgical procedures.
CPG works with shape-memory materials as well, incorporating them into medical devices to produce environmentally-responsive devices. Our devices respond to temperature, fluid environment, salinity and pH as appropriate.
Journal reference: Nature Communications, 10.1038/ncomms12919