The Lego form helps the material stick together and create a tight seal (Photo from Brown University)


Researchers at Brown University recently developed a new kind of hydrogel material that can be used for various soft robotic applications. The hydrogel is a new type of dual polymer material with the ability to respond to its environment in dynamic ways. The components, patterned by a 3D printer, are able to bend, twist, and stick together in response to treatment with certain chemicals. The results were published in a paper for the journal Polymer Chemistry.


One polymer contains covalent bonds, which provides strength and structural integrity. The other polymer has ionic bonds, which allows more dynamic behaviors like bending and self-adhesion. When combined, the polymers create a material that is soft, strong and responsive, which is ideal for creating a soft, robotic grip. For one test, researchers 3D printed a soft gripper capable of actuating on demand to pick up small objects.


“Essentially, the one polymer provides structural integrity, while the other enables these dynamic behaviors like bending or self-adhesion,” said Thomas Valentin, a recently graduated Ph.D. student in Brown’s School of Engineering and the paper’s lead author. “So putting the two together makes a material that’s greater than the sum of its parts.”


To create the new material, researchers combined one covalently crosslinked polymer, called PEGDA, with a polymer that’s ionically crosslinked, called PAA. Since the PEGDA has strong covalent bonds, it holds the material together while the PAA’s ionic bonds make it responsive. When the material is placed in an ion-rich environment, it makes the PAA crosslink making it more rigid. When the ions are removed, the material softens and swells as the ionic bonds break. This process also allows the material to be self-adhesive.


Hydrogels are an ideal material for microfluidic devices, especially those used in biomedical testing. They’re soft and flexible like human tissue, and typically nontoxic. But they’re usually problematic since they’re difficult to pattern with the complex channels and chambers needed in microfluidics. One possible solution to this is by using the material to create stackable LEGO-like blocks. Because the new material is 3D printed, it can be shaped like a Lego brick, which can then be carefully assembled and tightly sealed together to create customized microfluidic devices, or lab-on-a-chip, systems that can be used for drug screening, cell cultures, and other applications. And the blocks can be stored for long periods of time and still be effective.


It sounds promising, but the material isn’t quite ready yet. Researchers are still working on the polymers to make them more durable and functional. Once they’ve improved the material, it could help make building soft robotic components and lab-on-a-chip significantly easier.


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