Imagine structures that can change shape with the flip of a light switch.
An international team of researchers has found a way to 3D print hydrogels that respond to light, contracting and expanding like magic.
These new structures can act as remotely controlled devices, known as actuators.
Joe Tracy, a professor at North Carolina State University, explains, “We knew hydrogels could contract when heated and that gold nanorods could make them respond to light.
Our goal was to combine these ideas and 3D print hydrogels that react to light.”
Hydrogels are networks of polymers filled with water, found in items like contact lenses and diapers.
In this study, the researchers embedded gold nanorods in hydrogels to make them light-responsive.
When exposed to light, these gold nanorods heat up, causing the hydrogel to contract. When the light is turned off, the hydrogel cools and expands back to its original shape.
The researchers didn’t directly print hydrogels. Instead, they printed a special solution containing gold nanorods and the ingredients needed to form a hydrogel.
Julian Thiele, a co-author of the study and chair of organic chemistry at Otto von Guericke University Magdeburg, explains, “When this printed solution is exposed to light, it turns into a hydrogel with gold nanorods evenly distributed throughout.”
Printing the low-viscosity solution onto a regular surface would result in a puddle. To solve this, the team printed the solution into a translucent mixture of gelatin microparticles and water.
The printer nozzle can penetrate this mixture, creating the desired 3D shape. Light then converts the solution into a solid hydrogel.
Finally, the entire structure is placed in warm water, which melts away the gelatin, leaving the 3D hydrogel intact.
When exposed to light, the gold nanorods in the hydrogel convert light into heat, causing the hydrogel to contract and push out water. When the light is removed, the hydrogel cools and absorbs water, expanding back to its original size.
Melanie Ghelardini, the first author of the paper and a former Ph.D. student at NC State, notes, “We’ve shown that hydrogels can contract with light, not just heat. This 3D printing method means we can now trigger this effect remotely with light.”
Thiele adds, “3D printing hydrogels offers almost unlimited design possibilities and allows for preprogrammed motion during light-triggered contraction and expansion.”
This new method of creating light-responsive hydrogels is detailed in the paper “3D-Printed Hydrogels as Photothermal Actuators,” published in the open-access journal Polymers. This breakthrough opens the door to innovative applications where light, instead of direct heat, can control movements and actions in various devices and structures.
