Nanocellulose-based composites for 3D printed stimuli-responsive swelling hydrogel

Cellulose is a promising biomaterial ink for various applications, such as tissue engineering and soft robotics. Different cellulose derivatives have different advantages, depending on their surface area, fiber structures and rheological properties. In this work, the swelling capacity of carboxymethyl cellulose (CMC) was integrated with the stiffness of cellulose nanofibrils (CNF) to create multifunctional cellulose-based composites for additive manufacturing. CNF, CMC, and their composites show a higher storage modulus (G') than loss modulus (G") in the rheological study. This is indicative of the materials' ability to retain their printed structure post direct ink writing (DIW) 3D printing, thereby avoiding any structural collapse. Notably, the CNF at a concentration of 4.5 wt% demonstrates a higher storage and loss modulus, suggesting that CNF imparts the necessary rigidity to the CNF/CMC composite. Concurrently, CMC plays a pivotal role in water retention, which is a critical factor for the success of 4D printing processes. The CNF/CMC composite hydrogel can respond to stimuli and swell, which makes it suitable for biocompatible actuators. We demonstrated this by printing a prototype valve that can be reversibly closed and opened by dehydration/hydration cycles. The printed CNF/CMC composite structure has excellent mechanical properties, with tensile strength ranging from 55 MPa to 80 MPa, comparable with commercial PLA filament used in fused deposition modelling (FDM) 3D printing.