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

Insulation materials are essential for engineering efficiency, as they directly reduce energy losses or eliminate the need for extra components to compensate for them. However, most insulation materials are non-biodegradable polymers that significantly contribute to environmental degradation during production and disposal. This study explores the use of bioinspired chito-cellulosic materials -a family of biological composites known in structural applications for their low cost, versatile manufacturing, and ecological integration- as sustainable insulation. The study compares three chito-cellulosic variants with different cellulose compositions and evaluates their electrical, thermal, and acoustic insulation capabilities, as well as flammability, biodegradability, environmental impact, and mechanical properties. The insulating results are compared to conventional polyurethane foams, demonstrating lower thermal insulation capabilities, similar electrical insulation, and better acoustic insulation. Moreover, they offer the advantages of being 3D-printable, fully biodegradable in environmental conditions, and fireproof, highlighting their potential as a viable green alternative to synthetic insulators.

JTD Keywords: Cellulose, Chitosan, Flam, Foam, Insulation

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

A method for the simultaneous (bio)chemical and topographical patterning of enclosed structures in poly(dimethyl siloxane) (PDMS) is presented. The simultaneous chemical and topography transference uses a water-soluble chitosan sacrificial mold to impart a predefined pattern with micrometric accuracy to a PDMS replica. The method is compared to conventional soft-lithography techniques on planar surfaces. Its functionality is demonstrated by the transference of streptavidin directly to the surface of the three-dimensional PDMS structures as well as indirectly using streptavidin-loaded latex nanoparticles. The streptavidin immobilized on the PDMS is tested for bioactivity by coupling with fluorescently labeled biotin. This proves that the streptavidin is immobilized on the PDMS surface, not in the bulk of the polymer, and is therefore accessible for use as signaling/binding element in micro and bioengineering. The use of a biocompatible polymer and processes enables the technique to be used for the chemical patterning of tissue constructions.

JTD Keywords: Biotechnology, Chitosan, Microfabrication, MEMs, Soft lithography

A technique for producing micrometer-scale structures over large, nonplanar chitosan surfaces is described. The technique makes use of the rheological characteristics (deformability) of the chitosan to create freestanding, three-dimensional scaffolds with controlled shapes, incorporating defined microtopography. The results of an investigation into the technical limits of molding different combinations of shapes and microtopographies are presented, highlighting the versatility of the technique when used irrespectively with inorganic or delicate organic moulds. The final, replicated scaffolds presented here are patterned with arrays of one-micrometer-tall microstructures over large areas. Structural integrity is characterized by the measurement of structural degradation. Human umbilical vein endothelial cells cultured on a tubular scaffold show that early cell growth is conditioned by the microtopography and indicate possible uses for the structures in biomedical applications. For those applications requiring improved chemical and mechanical resistance, the structures can be replicated in poly(dimethyl siloxane).

JTD Keywords: Biocompatible Materials/ chemistry, Cell Adhesion, Cell Culture Techniques/ methods, Cell Proliferation, Cells, Cultured, Chitosan/ chemistry, Crystallization/methods, Endothelial Cells/ cytology/ physiology, Humans, Materials Testing, Nanostructures/ chemistry/ ultrastructure, Nanotechnology/methods, Particle Size, Surface Properties, Tissue Engineering/methods

A technique for imparting micro- and nano-structured topography into the surface of freestanding thin sheets of chitosan is described. Both micro- and nanometric surface structures have been produced using soft lithography. The soft lithography method, based on solvent evaporation, has allowed structures similar to 60 nm tall and similar to 500 X 500 nm(2) to be produced on freestanding similar to 0.5 mm thick sheets of the polymer when cured at 293 K, and structures similar to 400 nm tall and 5 X 5 mu m(2) to be produced when cured at 283 K. Nonstructured chitosan thin sheets (similar to 200 mu m thick) show excellent optical transmission properties in the visible portion of the electromagnetic spectrum. The structured sheets can be used for applications where optical microscopic analysis is required, such as cell interaction experiments and tissue engineering.

JTD Keywords: Chitin/chitosan, Microstructure, Nanotopography, Polymerization, Soft lithography

Polymers with high glass transition temperatures, fluorinated ethylene propylene copolymer (FEP) and poly(ethylene naphthalate) (PEN), have been used in imprint lithography as a protective support layer and as a secondary mould, to imprint superficial structures into a polymer with a lower glass transition temperature, namely poly(methyl methacrylate) (PMMA). As a support layer, FEP replaces fragile silicon based supports for the production of freestanding, structured sheets of PMMA, useful, for example, in biomedical applications where transmittance optical microscopy is required. Secondary PEN moulds, produced by imprinting using silicon-based primary moulds, have been used to transfer sub-micrometer tall structures to a freestanding PMMA sheet. Similarly, hole structures, with different dimensions, have been embossed in both sides of a PMMA sheet simultaneously.

JTD Keywords: Polymer engineering, Embossing, Nanoimprint lithography, Biomedical applications

Micro- and nanoscale protein patterns have been produced via a new contact printing method using a nanoimprint lithography apparatus. The main novelty of the technique is the use of poly(methyl methacrylate) (PMMA) instead of the commonly used poly(dimethylsiloxane) (PDMS) stamps. This avoids printing problems due to roof collapse, which limits the usable aspect ratio in microcontact printing to 10:1. The rigidity of the PMMA allows protein patterning using stamps with very high aspect ratios, up to 300 in this case. Conformal contact between the stamp and the substrate is achieved because of the homogeneous pressure applied via the nanoimprint lithography instrument, and it has allowed us to print lines of protein similar to 150 nm wide, at a 400 nm period. This technique, therefore, provides an excellent method for the direct printing of high-density sub-micrometer scale patterns, or, alternatively, micro-/nanopatterns spaced at large distances. The controlled production of these protein patterns is a key factor in biomedical applications such as cell-surface interaction experiments and tissue engineering.

JTD Keywords: Soft lithography, Cell-adhesion, Microstructures, Fabrication, Stability, Patterns