Macroscopic assembly behavior of silk/lignin-based adhesive hydrogels: elementary macroscopic assembly

Macroscopic assembly has been explored as a strategy to construct appealing materials. Yet, an open question remains: does macroscopic assembly always occur one by one? In this study, a new kind of silk-based hydrogel was developed through incorporating lignin-related compounds <i>via</i> 1-ethyl-3-(3-pyl)-carbodiimide/<i>N</i>-hydroxysuccinimide (EDC/NHS)-mediated coupling chemistry. Thanks to the hydrogen-bond, hydrophobic, and π-π interactions, the hydrogels possessed the capability of adhesive and macroscopic assembly, which could be further tuned by introducing iron ions, as Fe³⁺ can form coordination bonds with lignin. Examination of the three-body macroscopic assembly behavior of the silk/lignin-based hydrogels was conducted as an approach towards answering the above question. Under the experimental conditions tested in this study, the answer is yes. However, it would be premature to draw a definitive conclusion on this question. This study aims to highlight this issue and stimulate further interest and research in diverse macroscopic assembly systems.