Staff member

Structural biomaterials achieve diverse mechanical functions by reconfiguring a small chemical palette, often via metal-ligand coordination in hydrated matrices. Despite biology's extensive use of such coordination in water-rich environments, engineered polysaccharide systems have primarily focused on mitigating moisture sensitivity rather than using hydration as a mechanical control parameter. Here we show that chitosan can be mechanically programmed by introducing divalent transition-metal ions (Cu, Zn, and Ni) and activating amines as inner-sphere donors through a simple post-casting neutralization. Multiscale characterization reveals metal-specific coordination states and water partitioning. These molecular differences produce distinct macroscopic behaviours: Zn increases dry strength and stiffness, Cu yields a more compliant and ductile response, and Ni inverts the hydration response, with immersion increasing modulus and strength. Because a single renewable backbone can span a wide mechanical range with minimal compositional changes, the approach reduces materials complexity in both manufacturing and end-of-life processing. Using only these minimal modifications, we fabricate a mechanically graded origami structure that integrates soft and stiff regions, demonstrating that coordination-mediated hydration control provides a scalable route to diverse mechanical designs from a single renewable biopolymer.

JTD

One of the most exploited properties of synthetic materials-and a limiting factor for the broader use of bio-based materials-is their durability and water stability, achieved through strong intermolecular interactions. However, this molecular stability also makes them persistent disruptors of ecological cycles, in contrast with biological structures, which undergo continuous molecular reconfigurations and use their environments to achieve both excellent mechanical properties and biodegradability. This study takes inspiration from chitinous cuticles to produce a biological material that uses water to gain strength and become waterproof. The process involves the vitrification of chitosan with small traces of nickel to create a dynamic network of intermolecular bonds using environmental water, resulting in a biomaterial that increases its strength when wet, an uncommon property previously observed in a few biological structures and never achieved artificially. The approach preserves the biomolecule's original chemistry and biodegradability while avoiding the strong organic solvents typically associated with bio-derived materials. The study describes the principle and demonstrates its application by manufacturing fully biodegradable and aquatically robust consumables and large objects made from Earth's second most abundant renewable molecule.

JTD

Flexible and biocompatible strain sensors are becoming increasingly important in fields such as health monitoring, wearable electronics, and environmental sensing because they offer significant advantages over conventional rigid systems. However, they lack the versatility and ecological and physiological biocompatibility necessary for broader integration within biological systems. Here, we describe the development of an inexpensive water-based plasticized chitosan-carbon black composite ink that can be used to produce conductive and biocompatible strain sensors. The ink can be applied to various surfaces, including skin, internal organs, and other biological tissues, using numerous methods, such as painting, dipping, and stamping. Furthermore, this unprecedented ability to attach and conform to biological surfaces allows the exploration of secondary sensing innovations, such as exploiting skin wrinkles to improve sensitivity. This study demonstrates that the ink exhibits a reliable change in electrical resistance in response to a wide range of motions, from subtle vibrations during speech and heartbeats to extensive articulations, like finger and elbow movements. This exceptional sensitivity range, biocompatibility, and the ink's low cost, biodegradability, and ease of removal enhance its applicability in sustainable, temporary, and customizable sensing solutions, highlighting its potential for versatile applications in human health monitoring, motion detection, and environmental sensing.

JTD Keywords: Blac, Chitin, Composites, Performance strain sensors