3D printing of lightweight, super-strong yet flexible all-cellulose structure.

• Lightweight & strong hierarchical structure was made from cellulose by 3D printing. • Its mechanical properties surpass most of other cellulose-based 3D monoliths. • The printed all-cellulose structure showed superb wet resilient performance. • The aerogel infilled honeycomb structure shows good thermal insulation properties. Lightweight yet strong cellular structural materials have long been sought for varied engineering applications due to the outstanding performance, and have been existing in numerous nature's designs such as wood, bone, and honeycomb. Cellulose is considered an ideal building block for such structure due to its natural abundance, low density, and high mechanical properties derived from the hydrogen bonded crystalline structure. However, restructuring pristine cellulose into 3D architectures with outstanding mechanical properties has always been a challenge. Here, a lightweight (∼90 mg/cm3) and super-strong (16.6 MPa compressive Young's modulus) honeycomb structure is constructed by 3D printing of all-cellulose ink. The 3D printed all-cellulose structure demonstrates switchable high elasticity (to withstand varied repetitive elastic deformation) at the wet state and high rigidity (to support over 15,800 of its own weight) at dry state. Such superb printing and mechanical properties can be ascribed to the controlled dissolution and regeneration of cellulose, as well as shear induced cellulose alignment during printing. In addition, the 3D printed all-cellulose honeycomb structure demonstrates good thermal insulation properties after filling with cellulose nanofibrils aerogel. [ABSTRACT FROM AUTHOR]