A study led by IBEC, based at the Barcelona Science Park of the University of Barcelona (PCB-UB), demonstrates that a single biomaterial, chitosan, can be modified with trace amounts of metal ions to adjust its stiffness and flexibility without altering its base chemistry. This technique is inspired by how insects construct their exoskeletons, combining rigid and flexible parts in one piece.
This approach aims to overcome the recycling challenges of modern products, often composed of multiple materials. According to Javier G. Fernández, the study's leader, if a single material can behave differently in various zones, the recycling or composting process is simplified. Living organisms, like insects, already employ this "material economy" to achieve diverse functionalities with a single base polymer.
The team used chitosan, a derivative of chitin, and introduced copper, zinc, or nickel ions. Interactions with these ions modify the polymer chain associations. Zinc-doped chitosan proved stronger and stiffer, copper-doped chitosan was more ductile, and nickel-doped chitosan exhibited a unique property of increased stiffness when wet, a phenomenon previously observed in earlier IBEC studies.
As a proof of concept, researchers constructed an origami-inspired fan-shaped structure, combining rigid and flexible chitosan in a continuous sheet. This component can be controllably folded and unfolded, simulating insect wing movement without glue, seams, or separate parts. The study also analyzed the materials' degradation in soil, with doped versions degrading at different rates.
“"Nature commonly changes the local properties of a single material to gain efficiency. An insect builds its entire exoskeleton as a single continuous piece, yet it includes very flexible parts, like leg joints, and very rigid parts, like the thorax or wings. This is efficient to produce, as the animal only needs to adjust a single process, and it is also mechanically efficient, because a structure without joints is much more resistant than one built by joining separate pieces."
