Initially, this material can be pulled and stretched out. Doing this applies a force to it, causing the internal structure to crystallize within segments called “chains.” These chains rapidly align in the same direction as crystals begin to form inside them, and consequently, it can hold any shape when left freestanding. This stabilizing process is known as “strain-induced crystallization.”
Although shape-changing polymers aren’t new, this novel material is able to respond dynamically to body heat. It retains its solid form until it’s exposed to a temperature of around 35°C (95°F), whereupon the crystals melt and the internal chains collapse and fall out of alignment.
The key to figuring out how to fine tune a material to respond to such a specific temperature so rapidly lay within its molecular structure. The researchers worked out that by adding molecular linkers – miniature struts that do not crystallize – to the individual chains, they inhibit, but not prevent, crystallization in the material. By tinkering with the material in this way, the team managed to add just enough inhibiting linkers to make body temperature the precise threshold for crystallization.
As this material can be both flexible and rigid around a human body, it could be used in a range of medical science applications, including in the creation of artificial skin.
“Tuning the trigger temperature is only one part of the story,” said Mitchell Anthamatten, a professor of chemical engineering at the University of Rochester, in a statement. “We also engineered these materials to …perform more mechanical work during their shape recovery.”
The internal structure of the material has been designed so that it can contain and store a vast amount of elastic or strain energy, similar to how a spring stores elastic energy when it is compressed. Incredibly, just one gram of this new shape-shifting material could lift a liter of water. A kilogram (2.2 pounds) could lift up to four fully-grown African lions. In terms of medical applications, this could be used to make prosthetics that have unprecedented strength.
In material science, you should never underestimate the power of the very small. Just last week, engineers created the world’s smallest lattice, and despite the fact that 150 lattices can fit on the head of a single pin, it can withstand thousands of atmospheric pressures.