Kirigami Dragon-Inspired Structural Design for Super Tough and Highly Ductile Nanocellulose Films.

Cellulose nanofibril (CNF) films hold great promise as advanced flexible biomaterials for high-value applications. However, their inherently low ductility and limited toughness still pose major challenges for broader commercial utilization. Herein, a structural design inspired by a 3D kirigami dragon is presented, which incorporates highly homogeneous, submicrometer-sized lignin colloidal spheres as soft zones into an interwoven network of rigid CNFs, thus greatly enhancing the ductility and toughness of CNF films. Such a structure allows the film to stretch over large areas under stress due to the conformable deformability of the uniform submicron soft zones. Specifically, the as-prepared CNF films containing monodispersed lignin colloidal spheres unfold an elongation of 54.25% and a toughness of 60.58 MJ/m3, which represent increases of 3.4 times and 3.7 times, respectively, compared to pure CNF films. Furthermore, they demonstrate the ability to accurately detect tensile strain signals and body motion, with potential applications in wearable sensors. This work provides a structural design strategy to dramatically improve the toughness and ductility of CNF films, advancing their potential as sustainable alternatives to petroleum-based plastics.