CREDIT: Wong Lab / University for Browsing
Researchers at Brown University have shown a way to use gum oxide (GO) to add some backbone of hydrogel materials made from alginate, a natural material derived from algae, which is currently used in various biomedical applications. In one paper published in the journal Carbon, researchers describe the 3-D printing method for making complex and durable alginate-GO structures that are far more robust and more resistant to fractures containing alginate.
"One limiting factor in the use of alginate hydrogels is that they are very fragile – they tend to disintegrate under mechanical strains or in low salt solutions," said Thomas Valentin, a PhD student at Braunschot for Engineering who led the job . "What we have shown is by incorporating graphene oxide agents, we can make these structures much stronger."
The material is also capable of becoming tougher or softer in response to various chemical treatments, which means it can be used to make "smart" materials that can react to their environment in real time, the survey shows. In addition, alginate-GO retains the ability of alginate to dispense oils, giving it the new material potential as a healthy antifouling layer.
The 3-D printing method used to make the materials is known as stereolithography. The technique uses ultraviolet laser control controlled by a computer design system to monitor the patterns through the surface of the photoactive polymer solution. Light causes polymer to connect together, forming solid 3-D structures from the solution. The tracking process is repeated until the whole object builds a layer-by-layer from the bottom up. In this case, the polymer solution is made using sodium alginate, mixed with graphene oxide leaves, a carbon-based material that forms nanotubes with a thickness of one atom that are stronger than pounds of steel.
One advantage of the technique is that the sodium alginate polymers connect through ionic bonds. Bonds are strong enough to hold the material together, but can be broken by certain chemical treatments. It gives the material the ability to dynamically respond to external stimuli. Earlier, Brown's researchers found that this "ion cross-linking" could be used to create alginate materials that are degraded on demand, rapidly dissolving when treated with a chemical that removes them from the internal structure of the material.
For this new study, researchers wanted to see how gum oxide could alter the mechanical properties of alginate structures. They showed that alginate-GO can be made twice as hard as alginate, and much more resistant to failure by shooting.
"The addition of gum oxide stabilizes the alginate hydrogen gel with hydrogen bonding," said Jan J.. Wong, assistant professor of engineering in Brown and senior author of the newspaper. "We think the fracture resistance is due to the cracks that need to bypass the separated graphene leaves, rather than being broken, albeit homogeneous alginate."
Additional stiffness allowed researchers to print structures that had oversized parts, which would be impossible only with the use of alginate. In addition, increased stiffness does not prevent alginate-GO also respond to external stimuli such as alginate alone. Researchers have shown that by bathing materials in a chemical that removes its ions, the materials have grown and become much softer. The materials regained their stiffness when they were returned by bathing in ionic salts. Experiments have shown that the stiffness of the materials can be adjusted to a factor of 500 by changing their external ionic environment.
This ability to change its stiffness can make alginate-GO useful in various applications, scientists say, including dynamic cell cultures.
"You can imagine a scenario where you can imitate living cells in a hard environment, and then immediately move into a softer environment to see how the same cells can respond," Valentin said. It can be useful in studying how cancer cells or immune cells migrate across different organs throughout the body.
And since alginate-GO retains the powerful properties of pure alginate oil, the new material can make an excellent layer to keep oil and other dirty matter from building surfaces. In a series of experiments, the researchers showed that the alginate-GO coating could keep the oil from blurring on the surface of the glass under conditions of very salty water. It could make alginate-GO hydrogels useful for coatings and structures used in marine conditions, researchers say.
"These composite materials can be used as a sensor in the ocean, which can store readings during oil leakage or as a cautious layer that helps keep the clean on the ship," Wong said. The additional stiffness given by graphene would make such materials or coatings more durable than the alginate itself.
The researchers plan to continue experimenting with the new material, seeking ways to streamline their production and continue to optimize their properties.
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