A team at Brown University has combined seaweed-derived alginate with graphene oxide to create a composite that is durable and can respond dynamically to its environment. The new hybrid material could be used in the design of other “smart” materials that can respond to external stimuli, making it a good fit for next-generation biomedical, environmental, and marine applications, they said in a Brown University news release.
Brown University researchers have created a hybrid material out of seaweed-derived alginate and the nanomaterial graphene oxide. The 3D printing technique used to make the material enables the creation of intricate structures including the one above, which mimics the atomic lattice of graphene. (Image source: Wong Lab / Brown University)
Scientists already use alginate—derived from seaweed—in biomedical applications, but one limiting factor with hydrogels made from the material is that they are very fragile, said Thomas Valentin, a Ph.D. student in Brown’s School of Engineering, who led the research. “They tend to fall apart under mechanical load or in low salt solutions,” he said in the news release.
The work of the research team managed to reinforce the material by using the versatile, carbon-based material graphene, making it more durable for various applications, Valentin said. “What we showed is by including graphene oxide nanosheets, we can make these structures much more robust,” he said.
Researchers used a 3D-printing method called stereolithography to develop the material. This technique uses an ultraviolet laser controlled by a computer-aided design system to trace patterns across the surface of a photoactive polymer solution—which, in this case, was a sodium alginate mixed with sheets of graphene oxide.
In this process, the light causes the polymers to link together, forming solid 3D structures from the solution. The tracing process is repeated until the layering effect builds an entire object from the bottom up.
A Responsive Material
Another aspect of the technique is what causes the material’s ability to respond dynamically to external stimuli, researchers said. This aspect is the linking of the sodium alginate polymers through ionic bonds, which are strong enough to hold the material together, but can be broken by certain chemical treatments.
This so-called “ionic crosslinking”—proven before by the researchers in other experiments—can be used to create alginate materials that degrade on demand, rapidly dissolving when treated with a chemical that sweeps away ions from the material’s internal structure, they said. Researchers published a paper on their work in the journal Carbon.
New Material Twice as Stiff—Or More
In the most recent study, researchers also observed how graphene oxide changes the mechanical properties of alginate structures, demonstrating how the new composite could be made twice as stiff as alginate alone and far more resistant to failure through cracking, said Ian Y. Wong, an assistant professor of engineering at Brown.
“The addition of graphene oxide stabilizes the alginate hydrogel with hydrogen bonding,” he said. “We think the fracture resistance is due to cracks having to detour around the interspersed graphene sheets, rather than being able to break right though homogeneous alginate.” This added robustness allowed the team to print structures that had overhanging parts—something that could not have been possible with alginate alone.
They also showed other properties of the new material. For instance, by bathing the materials in a chemical that removes its ions, the materials swelled up and became much softer. They then regained their stiffness when ions were restored through bathing in ionic salts. Further experiments showed that the materials’ stiffness could be tuned over a factor of 500 just by varying their external ionic environment.
This ability to vary the stiffness of the material makes it potentially useful for a number of applications, one of which is for dynamic cell cultures, Valentin said. “You could imagine a scenario where you can image living cells in a stiff environment and then immediately change to a softer environment to see how the same cells might respond,” he said. This application could help scientists study how cancer cells or immune cells migrate through different organs throughout the body.
Useful as a Coating
Researchers also showed that the new material is oil-resistant, making another potential use as a coating to keep oil and other grime from building up on surfaces, they said. They used highly saline conditions to test this use, demonstrating the hybrid’s potential for materials used in marine applications, where its durability and stiffness also can come in handy, Wong said.
“These composite materials could be used as a sensor in the ocean that can keep taking readings during an oil spill, or as an antifouling coating that helps to keep ship hulls clean,” he said.
The team plans to continue to work with the material to find new uses, optimize its properties, and find efficient ways to fabricate and mass produce the material, researchers said.
Elizabeth Montalbano is a freelance writer who has written about technology and culture for 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco, and New York City. In her free time, she enjoys surfing, traveling, music, yoga, and cooking. She currently resides in a village on the southwest coast of Portugal.
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