Biobased fibers made from renewable sources could be useful for a variety of applications, including textiles or medical devices. But it can be difficult to make long, continuous threads from these materials. Now, researchers from the University of São Paulo and Aalto University have made sturdy, flexible threads from a combination of chitin nanofibers extracted from crab shells and alginate, a compound found in seaweed (ACS Sustainable Chem. Eng. 2019, DOI: 10.1021/acssuschemeng.9b06099). The team studied how differences in the concentration of each component, the size of the nanofibers, and other variables affect the mechanical properties and spinnability of the final thread. With this information, the researchers were able to produce strong, flexible threads continuously, limited only by the volume of each component.
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The following is the script for the video.
Kerri Jansen (voice-over): These two droplets contain biomaterials that, when combined, cling together to form a sturdy and flexible thread. Scientists want to use biobased threads for a variety of applications, including high-performance textiles and tissue engineering. But first they’ll need to develop a simple, scalable production process. And it can be hard to make long, continuous threads with these biomaterials.
In this case, researchers wanted to make a fiber that combined the properties of chitin, a strong, antimicrobial material derived from crab shells, and alginate, a compound found in seaweed that is already used for wound healing and tissue engineering. When the researchers designed this material, they knew that the negatively charged alginate would be attracted to chitin nanofibers, which they had modified to have a positive charge. They found that when a solution of alginate contacts a suspension of chitin nanofibers, the alginate wraps around the chitin nanofibers, forming fibrils that align in parallel as the thread is drawn upward.
The researchers studied how variables like the concentration of each component and the size of the chitin nanofibers affected the properties of the composite thread. For example, they found that longer nanofibers made the thread stronger, but it also broke more frequently, possibly because the larger nanofibers more easily form clumps that can act as defects. Shorter nanofibers gave the thread more flexibility and made it easier to spin continuously. In lab tests, the team found that the composite threads were about as strong as threads made only from the crab-shell-derived chitin. But they had the bonus of flexibility from their alginate. The researchers plan to explore how further tweaks might improve the mechanical properties of their new threads.