Researchers from Brown University have come up with a way to use graphene oxide (GO) to improve the structural integrity of hydrogel materials made from alginate. Alginate is a natural material derived from seaweed that is currently in use in a variety of biomedical applications. Alginate-GO structures are significantly stiffer and more resistant to fracture than alginate alone.
“One limiting factor in the use of alginate hydrogels is that they’re very fragile — they tend to fall apart under mechanical load or in low salt solutions,” said Thomas Valentin, a Ph.D. student in Brown’s School of Engineering who led this project. “What we showed is by including graphene oxide nanosheets, we can make these structures much more robust.”
The new material is also capable of becoming stiffer or softer in response to chemical treatments, meaning it could be used to create smart materials that can respond to their surroundings in real time. It also retains alginate’s ability to repel oils, hence it could be used as an antifouling coating.
The new material was constructed using a 3D printing technique known as stereolithography, which utilizes a computer-controlled ultraviolet laser to trace patterns across the surface of a photoactive polymer solution. The light causes the polymers to link together, forming a 3D structure. This process is repeated until the structure is complete. In the case of Alginate-GO, the polymer solution is made using sodium alginate mixed with sheets of graphene oxide.
“The addition of graphene oxide stabilizes the alginate hydrogel with hydrogen bonding,” said Ian Y. Wong, an assistant professor of engineering at Brown. “We think the fracture resistance is due to cracks having to take a detour around the interspersed graphene sheets rather than being able to break right through homogeneous alginate.”
The added stiffness given to alginate by graphene oxide has allowed the researchers to print structures with overhanging parts. This would have been impossible with alginate alone. Furthermore, the added stiffness did not prevent the Alginate-GO structures from responding to external stimuli. Brown researchers showed that by bathing the materials in a chemical that removes its ions, the materials swelled up and became much softer. Once bathed in ionic salts that restored that materials’ ions, they regained their stiffness.
“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,” said Wong.
For now the researchers continue to experiment with this new material, looking for new ways to make its manufacture more efficient and optimize its properties.