Through a new process called microstereolithography, researchers at the Massachusetts Institute of Technology, in conjunction with work from the Singapore University of Technology and Design, have been able to print micron-scale three-dimensional structures that can “remember” their original shapes.
The researchers further describe that size is important in a project like this because larger shape-memory polymers take longer to respond to stimuli; which is why they formed micron-scale objects. Of course, this is just the beginning but researchers hope to eventually be able to use body temperature as a trigger for these objects.
MIT Associate Professor of mechanical Engineering, Nicholas X. Fang explains, “If we can design these polymers properly, we may be able to form a drug-delivery device that will only release medicine at the sign of a fever.”
Fang also goes on to describe the process they used: microstereolithography.: “We’re printing with light, layer by layer. It’s almost like how dentists form replicas of teeth and fill cavities, except that we’re doing it with high-resolution lenses that come from the semiconductor industry, which give us intricate parts, with dimensions comparable to the diameter of a human hair.”
While the process uses a 3D printer, though, they are calling it “4D printing” because the 3D-printed objects are designed to change over time (which is the 4th dimension).
Still, even when using the micron-scale objects, the researchers found that grabbing claws, coils, flowers, and more could be stretched to a length three times their original size and could be twisted out of their original shape without showing sign of strain. More specifically, when these structures were exposed to a temperature range of 40 to 180 degrees Celsius (equivalent to 104 to 356 degrees Fahrenheit), they could return to their original shape in just a matter of seconds.
Fang also explains that, for example, “a flower can release pollen in milliseconds [but] it can only do that because its actuation mechanisms are at the micron scale.”
This is a practical description of the science behind the technology, and a solid foundation for what Fang hopes could be applications in the future. They are now looking for combinations of polymers to improve the size and capabilities of these shape-memory materials.