Bio-Inspired Toughening Mechanisms in Densified Delignified Wood Laminates

Natural materials exhibit extraordinary mechanical properties, allowing them to withstand some of the most demanding environments. What sets them apart is their ability to overcome the typical trade-off between strength and toughness, thanks to their intricately designed microstructures that enable multiple energy dissipation mechanisms. In this work, we present a significant advancement in the creation of a bio-based material that not only demonstrates exceptional fracture resistance and high strength but also successfully incorporates a range of bio-inspired toughening mechanisms, mirroring nature's strategies for durability and resilience. By employing a combination of bio-inspired toughening mechanisms—including micro-scale suturing and nano-scale interlocking—our material achieves high toughness, far exceeding that of its constituent components.<br/>We have employed a rigorous process of wood delignification and vacuum-assisted densification, which effectively reduces the porous structure of wood and enables the formation of tightly packed, unidirectional cellulose layers. This approach allows us to strategically laminate the material in both radial and tangential orientations, taking advantage of the natural interlocking of wood cells as well as native wood’s material gradients. By integrating the inherent microstructures of wood into the design, we enhance the material's mechanical performance, creating a highly organized architecture that maximizes not only strength but also fracture resistance across multiple length scales. We validate the great damage-resistance performance of our modified wood using a comprehensive set of advanced techniques, including microcomputed tomography (micro-CT), scanning electron microscopy (SEM), fracture testing, and digital image correlation (DIC). These methods allow us to closely observe and quantify the material's behavior post failure, revealing insights into its toughening mechanisms. Our analysis reveals that by leveraging bio-inspired toughening mechanisms such as crack deflection, crack trapping, and fiber bridging, our densified wood laminate demonstrates fracture strengths of up to 350 MPa and fracture energy as high as 60 KJ/m².<br/>When comparing our bio-based laminate to other major material classes, its damage tolerance surpasses that of native wood and virtually all technical and non-technical ceramics and polymers, as well as several pure metals and metallic alloys, including magnesium and aluminum. These comparisons highlight the outstanding mechanical properties of our material, positioning it as a remarkable alternative in fields where high-performance, lightweight, and durable materials are crucial.<br/>The presented bio-inspired densified wood combines low density, cost-effectiveness, and recyclability. This combination of features makes our novel material highly attractive for a wide range of advanced engineering and structural applications, from aerospace to construction, where sustainability and performance are key considerations.