Metal Coordination‐Mediated Functional Grading and Self‐Healing in Mussel Byssus Cuticle

• Published in: Advanced science Vol. 6; no. 23; pp. 1902043 - n/a
• Main Authors: Xu, Quan, Xu, Meng, Lin, Chun‐Yu, Zhao, Qiang, Zhang, Rui, Dong, Xiaoxiao, Zhang, Yida, Tian, Shouceng, Tian, Yu, Xia, Zhenhai
• Format: Journal Article
• Language: English
• Published: Germany John Wiley & Sons, Inc 01.12.2019; John Wiley and Sons Inc; Wiley
• Subjects: Communication; Communications; density functional theory; Etching; iron complex; Laboratories; Lasers; Mollusks; mussels; Oxidation; self‐healing; Spectrum analysis; tensile tests; Tribology; China; Germany; iron complex; mussels; tensile tests; density functional theory; self‐healing
• ISSN: 2198-3844; 2198-3844
• DOI: 10.1002/advs.201902043

Metal‐containing polymer networks are ubiquitous in biological systems, and their unique structures enable a variety of fascinating biological behaviors. Cuticle of mussel byssal threads, containing Fe‐catecholate complexes, shows remarkably high hardness, high extensibility, and self‐healing capability. Understanding strengthening and self‐healing mechanisms is essential for elucidating animal behaviors and rationally designing mussel‐inspired materials. Here, direct evidence of Fe3+ and Fe2+ gradient distribution across the cuticle thickness is demonstrated, which shows more Fe2+ inside the inner cuticle, to support the hypothesis that the cuticle is a functionally graded material with high stiffness, extensibility, and self‐healing capacity. The mechanical tests of the mussel threads show that both strength and extensibility of the threads decrease with increasing oxygen contents, but this property degradation can be restored upon removing the oxygen. The first‐principles calculations explain the change in iron coordination, which plays a key role in strengthening, degradation, and self‐healing of the polymer networks. The oxygen absorbs on metal ions, weakening the iron‐catecholate bonds in the cuticle and collagen core, but this process can be reversed by sea water. These findings can have important implications in the design of next‐generation bioinspired robust, highly extensible materials, and catalysis. Evidence of Fe3+ and Fe2+ gradient distribution across the cuticle thickness of bypass thread is provided, which supports that the cuticle is a functionally graded material with high stiffness, extensibility, and self‐healing capacity. The oxygen absorbed on metal ions can weaken the iron‐catecholate bonds in the cuticle and collagen core, but cuticle can heal itself in sea water.