Bioinspired Hierarchical Composite Hydrogels via Shear-Assembled Direct Ink Writing Technology

Soft materials, such as hydrogels, have garnered significant attention in fields like wearable electronics, soft robotics, biomedicine, and energy technology, thanks to their unique combination of high electrical conductivity, stretchability, biocompatibility, and self-healing capabilities. Nevertheless, the inherent brittleness of hydrogels has presented a challenge to their practical application. Biological soft tissues, like tendons and cartilage, exhibit remarkable strength, flexibility, and message-transmission capabilities due to their composite composition and intricate hierarchical structures. Drawing inspiration from nature, we have developed a promising approach—shear-assembled direct ink writing—to strengthen and toughen hydrogels by incorporating secondary-phase fillers and creating bioinspired hierarchical structures. This process involves applying shear-force-induced self-assembly extrusion printing of nanoceramic platelets enhanced hydrogel inks, providing control over nano- to sub-micro scale structures. Additionally, the filaments can be 3D printed into free-form bioinspired architectures, ranging from micro- to macro-scale, such as unidirectionally aligned, Bouligand, and crossed lamellar configurations. By tailoring the composition, nanoceramic alignment, and printing patterns, the composite hydrogel exhibits multiple strengthening and toughening mechanisms across different scales. Through the application of this technology, we have successfully produced flexible and robust nanoceramic-hydrogel composites with high ceramic compositions for creating reconfigurable structures. Furthermore, we have developed flexible bioceramic-hydrogel composites with potential applications in bone tissue engineering, as well as strong and tough conductive composite hydrogels for use in flexible electronics.