Biopolymer-based 4D printing: Achieving heightened printability and shape morphing with composites of alginate and calcium ion-infused 2D vermiculite

4D printing has garnered widespread interest due to its potential to revolutionize the fabrication of stimuli-responsive structures. Despite its promise, the field faces challenges with biopolymer utilization, particularly issues related to processability and structural inertia. Here, we present a pioneering endeavor aimed at surmounting these hurdles, focusing on sodium alginate (SA) as a model biopolymer, amalgamated with calcium ion-infused 2D vermiculite sheets (CaV), culminating in the synthesis of composite hydrogels via a novel in-situ physical crosslinking methodology. The resultant hydrogels exhibit notable gel-like behavior and substantially enhanced rheological characteristics and 3D printability, leading to printed constructs with excellent shape fidelity and mechanical properties. Our investigation underscores the pivotal role of vermiculite sheets' notable physicochemical attributes, coupled with electrostatic interactions, in endowing these hydrogels with exceptional printability, as evidenced by the successful printing of various structures like grids, flower models, and cylindrical shapes. Furthermore, the 3D-printed structures manifest intriguing shape-morphing capabilities, transitioning from a planar configuration into tubular or folded forms within seconds to minutes, with morphing speed tunable via solvent treatments. Our work represents a significant stride in 4D printing, offering functional materials solutions utilizing biopolymers.