Anisotropic Nature of Lightweight Wooden Metamaterials with Mechanical/Thermomechanical Multistability

Abstract Nanoengineered wood provides a renewable structural material with 3D micro and nanoarchitectures, exhibiting many beneficial characteristics such as being lightweight in nature, mechanically strong, eco‐friendly, thermally insulation, and low carbon footprint. Most nanocellulose aerogels lack sufficient mechanical strength, while nanowood involves a trade‐off between mechanical strength and insulation performance. Here, a nanowood‐derived product with mechanical/thermomechanical multistability called a wooden metamaterial, which is ultrastiff yet lightweight, is designed and synthesized. The self‐healing behaviors of cellulose nanofibrils originally present in the cell walls and their combination with microscale mechanical constraints are utilized to form directional porous frameworks (porosity ≥98%) and encapsulated empty fiber lumen in predesigned macroscopic architectures. The wooden metamaterials are lightweight, showing ultrahigh specific strength (207.7 MPa cm 3 g −1 ), and ultrahigh anisotropy with an approximate factor of 4. Wooden metamaterials have overcome the mechanical/thermomechanical deficiencies of existing building materials and advanced aerospace thermal insulators, and have great potential for revolutionizing architecture and manufacturing industries, particularly as a lightweight, eco‐friendly, scalable, energy‐efficient, and cost‐effective.