Constructing onion-like multilayered hydrogels from natural polymers by diffusion reaction coupled with substrate effect.

Multilayered natural polymer-based hydrogels possess excellent properties and hold great promise for applications in materials science, food technology, and biomedicine. However, constructing such complex structures remains challenging due to difficulties in achieving precise control and ensuring operational convenience. To address these challenges, we propose a facile strategy based on a diffusion reaction combined with substrate effect to construct onion-like multilayer natural polymer-based hydrogels, using calcium alginate hydrogels as a model system. Hydrogels formed on hydrophobic substrates present multilayered, concentric grooved structures, while those formed on hydrophilic substrates display a more homogeneous morphology. Mechanical testing reveals that the layered hydrogels exhibit higher compressive and tensile strength compared to flat hydrogels. Additionally, the layered hydrogels could reduce friction and enhance wear resistance under load conditions, a result attributed to their unique surface architecture. These findings provide new insights into how surface properties can be utilized to control hydrogel structure and underscore the potential of layered hydrogels for applications that require sustained mechanical stress and low friction, such as joint implants and soft robotics.