This biomaterial becomes stronger when wet

Most biobased materials soften when they’re wet. A team led by Javier G. Fernández at the Institute for Bioengineering of Catalonia has now shown that the opposite can happen: add a dash of nickel to chitosan, and the material grows stronger in water.Chitosan, derived from chitin in shrimp shells, typically weakens when water slips between its polymer chains. But when the researchers incorporated small amounts of nickel ions into the chitosan films and then immersed them in water, the material’s tensile strength increased by nearly 50% (Nat. Commun. 2026, DOI: 10.1038/s41467-026-69037-4).The idea stemmed from biology. Earlier studies show that when metals such as zinc are removed from the teeth of sandworms, the structures soften in water. That observation prompted the team to test whether introducing a metal ion into a reconstituted chitosan system could control how the polymer behaves in wet conditions.“Water is usually considered a degrading factor,” says coauthor Akshayakumar Kompa. “Here it becomes an integral component.” Nickel acts as a connector, loosely binding to the polymer while also attracting water molecules. Those water molecules bridge neighboring chains, forming a dynamic network that redistributes stress instead of concentrating it.About 87% of the nickel leaches out during the first immersion. The strengthening effect remains, which suggests that only a small fraction of nickel is needed to connect the polymers. The team reuses the released nickel solution to fabricate the next batch and describes the approach as a zero-waste loop.“Chitosan generally degrades within weeks,” Kompa says. “The nickel-modified material slows biodegradation.