Isotropic Bouligand Wood with High Strength and Toughness

Achieving structural materials that combine high strength, toughness, and sustainability remains a significant challenge in materials science and engineering. Wood, as a renewable and widely available natural resource, presents promising potential but is limited by its intrinsic anisotropy and mechanical property variations across directions. Inspired by the Bouligand architecture─composed of helicoidally stacked layers of aligned fibers─we developed a straightforward and effective approach to overcome these limitations. By exploiting the natural orientational alignment of wood fibers, we chemically treated the wood to expose hydroxyl groups of cellulose and then densified the wood by helicoidal stacking to obtain Bouligand wood. This bioinspired design yielded a wood-based material exhibiting in-plane isotropy alongside exceptional strength (∥235.2 MPa, ⊥203.9 MPa) and toughness (∥10.8 MPa·m1/2, ⊥15.3 MPa·m1/2), outperforming many commonly used polymers and metals. The helicoidal architecture facilitates crack deflection and bridging mechanisms, substantially enhancing toughness, while hydrogen bonding strengthens the cellulose network and improves interfacial adhesion. Integrating structural design with cellulose's inherent molecular interactions enabled us to significantly reduce wood's anisotropy and realize a novel, high-performance wood-based structural material with well-balanced mechanical properties. This sustainable, mechanically isotropic material offers considerable promise for applications in construction, automotive, aerospace, and other engineering fields.