Researchers from the Institute for Bioengineering of Catalonia (IBEC), in collaboration with the Singapore University of Technology and Design (SUTD), have created an advanced material made from biodegradable chitosan that gets stronger when wet rather than breaking down.
The research team behind the study suggests their material could offer a viable alternative to harmful plastics and other plastic alternatives that break down when exposed to water, including environmentally damaging forms like single-use plastic cups and water bottles.
Material That Gets Stronger When Wet Inspired by Worm Fangs
According to study leader and IBEC research professor Javier G. Fernández, most plastics and other customized polymers are designed to resist environmental conditions, including water. However, the durability of plastics has resulted in a growing environmental crisis, including the discovery of microplastics in the human body.
Scientists have explored biodegradable materials with a much lower environmental impact than plastics. Unfortunately, these alternatives break down more easily than plastic. The breakdown of biodegradable plastic alternatives is even more pronounced when these materials come into contact with water.
To combat this issue, engineers have turned to chemical modifications or water repellent coatings. While these changes can extend the lifespan and increase the viable applications of plastic alternatives, their addition undermines the environmental benefits of biomaterial-based plastic alternatives.
During the hunt for cheap, biodegradable, sustainable alternatives, Fernández noted a finding from a seemingly unrelated study on sandworm fangs. According to that previous work, removing zinc, a metal, from the fangs of the sandworm Nereis virens made them soften when exposed to water.
“This finding suggests that metals may play a key role in how natural materials interact with water,” the research team notes in a statement announcing their study.
A Combination of Chitosan and Nickel Becomes 50% Stronger After Immersion
Inspired by the sandworm fang study, the researchers explored whether metals could confer the same hydrophobicity to other biological materials. Given its wide availability as the second-most-abundant biological material on the planet, the researchers focused on chitosan, a naturally occurring polymer derived from crustacean shells such as shrimp.
Instead of incorporating zinc as the metal in their advanced material, the team chose the naturally occurring trace element nickel. In addition to dissolving readily in water, nickel readily interacts with chitin, the base material of chitosan, making it easy to study and fabricate
To test the concept, the research team mixed a batch of chitosan derived from discarded shrimp shells and nickel into a water solution. After removing the nickel that did not incorporate into the base material, the team processed the nickel-infused chitosan into thin films.
When the team tested the sheets, they not only resisted water, but also appeared to react to it. This interaction between the water and the chitosan/nickel hybrid material creates a network of weak, reversible bonds that continually break and reform due to the mobility of nickel ions and surrounding water molecules.
According to Fernández, the material’s constant reconfiguration at the microscopic level imbues it with a strength and resiliency that mirror those of biological systems that absorb stress and reorganize themselves.
“(This is) a material where being ‘soft’ at the molecular scale actually makes it stronger,” the professor explained.
Tests of the material’s resiliency showed that it resisted 50% more stress than before immersion in water.
Advanced Hybrid Material Remains ‘Biologically Pure in the Eyes of Nature’
Although the advanced material, which gets stronger when wet, was created in a lab, Professor Fernández said its chemical structure remains unchanged, making it “biologically pure in the eyes of nature” and completely biodegradable.
“It remains essentially the same molecule found in insect shells or mushrooms,” he explained.
Another benefit of the new material is its zero-waste manufacturing process. According to the study authors, most of the nickel that does not bind to chitosan during the water-immersion process is “released.” This leftover nickel is captured and reused for the next batch, achieving what the team described as a “100% efficiency in the use of nickel.”
“This approach enables the full recovery and reuse of nickel, drastically reducing environmental impact and costs,” they explained.
Unlike some modern, advanced materials, the new chitosan/nickel hybrid, which gets stronger when wet, is easily scalable due to the availability of the base materials. According to Akshayakumar Kompa, a postdoctoral researcher in Fernandez’s group and the study’s first author, the world produces an estimated one hundred billion tons of chitin each year.
“(That’s) equivalent to three centuries’ worth of plastic production,’ Kompa explained.
The research team notes that chitosan, which is primarily obtained from shrimp shells, can be obtained from organic waste or fungal byproducts. They also note that chitosan can be produced locally, reducing or eliminating transportation costs.
“Our goal is to integrate the production of these materials into the local ecosystem by using whatever form of chitosan is available nearby,” said Kompa. “The key is to adapt to local sources.”
Single Use Plastics Made From a Material That Gets Stronger When Wet
When discussing potential applications of a material that gets stronger when wet, the research team highlighted the agriculture, packaging, and fishing industries as primary beneficiaries. The researchers also formed their advanced material into watertight containers, offering an environmentally friendly alternative to single-use containers like cups and water bottles.
Because nickel and chitosan have previously been approved by the FDA for certain medical applications, the material could benefit companies designing waterproof coatings for medical devices and implants. Fernández and colleagues also suspect that other molecules beyond nickel can imbue chitosan with these unique properties.
“This is the first study,” the professor explained. “Now that we know this effect exists, we and others can search for new materials and new ways to achieve it.”
When discussing the study’s material science implications, the study authors said it “represents a shift in mindset away from the plastic age.” Instead of designing biological materials to behave like synthetic ones, the researchers said they “must design materials that work with the environment, not isolating from it.”
“For over a century, we have assumed that, in order to succeed in nature, materials must become inert,” Fernández explained. “This research shows the opposite: materials can thrive by interacting with their environment rather than isolating themselves from it.”
The study “Stronger when wet: Aquatically robust chitinous objects via zero-waste coordination with metal ions” was published in Nature Communications.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.