A new study led by the Biomedical Research Networking Center (CIBER), with participation from the Institute for Bioengineering of Catalonia (IBEC), has successfully programmed a biomaterial locally to be rigid in some areas and flexible in others, a strategy inspired by nature and used by insects and other arthropods.
This research, published in the Journal of Materials Chemistry A, has enabled the creation of articulated structures with rigid segments and flexible joints within a single continuous sheet. The approach, which uses only trace amounts of metals to modulate the properties of chitosan, a biopolymer derived from chitin, simplifies both the manufacturing and recycling of objects.
According to Javier G. Fernández, ICREA Research Professor at IBEC and study leader, the main bottleneck in current recycling is the recovery and sorting of different materials within a single product. If a single material can adapt to various functions, it can be recycled or composted as a single unit, eliminating the need for separation.
The researchers introduced copper, zinc, or nickel ions into dissolved chitosan. Interactions between these ions and the polymer allowed for modulation of the material's stiffness, strength, and flexibility. For instance, zinc-doped chitosan became stronger and stiffer, while copper-doped chitosan increased its elasticity. Notably, the nickel-doped material became stronger and stiffer when wet, unlike the zinc- and copper-doped versions, which weakened.
To demonstrate the utility of this local programming, the team constructed a fan-shaped, origami-inspired structure combining rigid (nickel-doped) and flexible (undoped) chitosan in a single sheet. This piece can be folded and unfolded in a controlled manner, much like an insect wing, without requiring glue, seams, or separate parts.
Soil degradation tests showed that zinc-doped films degraded completely within three weeks, copper-doped films lost approximately half their mass, and nickel-doped films, the toughest when wet, degraded more slowly.
These findings open a promising avenue for using biological materials to create diverse mechanical functions within a continuous structure. Next steps include assessing durability under repeated movement, adapting the process for large-scale manufacturing, and studying the materials' interaction with the environment.
