Herein, we report a facile and cost

Herein, we report a facile and cost-effective top-down method to prepare lightweight yet strong bulk densified bamboo with up to 1 GPa tensile strength and 400 MPa flexural strength. Figure 1A shows the schematic of our top-down approach to directly transform natural tubular bamboo into bulk densified bamboo by a flattening, delignification, and hot compression process. Prior to chemical treatment, each round bamboo stemwas made with a linear cut to remove the inner node sections, softened with high-pressure steam, and flattened into a bulk bamboo material using a horizontal pressing apparatus. The flattened bulk bamboo was then chemically treated to partially remove the lignin and hemicellulose from its lignocellulosic cell walls, leading to swelling and softening of the well-aligned structure of the cellulose fibers. Upon hot-pressing, the paren- chyma cells and lumens of the bamboo cellular structure perpendicular to the growth direction are fully compressed, resulting in a densified piece of bamboo with a 70% reduction in thickness. The densified bamboo notably exhibits a record high tensile strength up to 1 GPa, surpassing those of various wood natural materials, engineered steel, strong metallic alloys, and even the recently developed super-strong densified wood reported by our group (Figure 1B). As one of the fastest growing plants on Earth, bamboo features a peak growth rate up to 100 cm per day, which is far faster than all kinds of wood (typically 0.1–0.4 cm per day) (Figure 1C). The scalable structural materials with extraordinary mechanical strength and toughness from the fast-growing bamboo can open up a range of emerging applications such as lightweight vehicles for energy saving, aerospace and buildings.