Protein-based biogenic materials provide important inspiration for the development of high-performance polymers. The fibrous mussel byssus, for instance, exhibits exceptional wet adhesion, abrasion resistance, toughness and self-healing capacity–properties that arise from an intricate hierarchical organization formed in minutes from a fluid secretion of over 10 different protein precursors. However, a poor understanding of this dynamic biofabrication process has hindered effective translation of byssus design principles into synthetic materials. Here, we explore mussel byssus assembly in Mytilus edulis using a synergistic combination of histological staining and confocal Raman microspectroscopy, enabling in situ tracking of specific proteins during induced thread formation from soluble precursors to solid fibres. Our findings reveal critical insights into this complex biological manufacturing process, showing that protein precursors spontaneously self-assemble into complex architectures, while maturation proceeds in subsequent regulated steps. Beyond their biological importance, these findings may guide development of advanced materials with biomedical and industrial relevance.
Mussel mooring made mighty by metals Mussels produce an exceptional proteinaceous adhesive so they can withstand waves and currents. Metal ions bound to modified tyrosine residues play an important role in reinforcing the adhesive. Priemel et al . brought together a variety of spectroscopy and microscopy techniques to study the cellular mechanisms involved in adhesive fabrication in mussels (see the Perspective by Wilker). They found that metal ion–rich vesicles are secreted alongside vesicles containing the adhesive protein and mix in a microfluidic-like process within interconnected microchannels found in the lateral duct of the mussel foot to create porous, adhesive plaque filaments. —MAF
Inspired largely by the role of the posttranslationally modified amino acid dopa (DOPA) in mussel adhesion, catechol functional groups have become commonplace in medical adhesives, tissue scaffolds, and advanced smart polymers. Yet, the complex redox chemistry of catechol groups complicates cross-link regulation, hampering fabrication and the long-term stability/performance of mussel-inspired polymers. Here, we investigated the various fates of DOPA residues in proteins comprising mussel byssus fibers before, during, and after protein secretion. Utilizing a combination of histological staining and confocal Raman spectroscopy on native tissues, as well as peptide-based cross-linking studies, we have identified at least two distinct DOPA-based cross-linking pathways during byssus fabrication, achieved by oxidative covalent cross-linking or formation of metal coordination interactions under reducing conditions, respectively. We suggest that these end states are spatiotemporally regulated by the microenvironments in which the proteins are stored prior to secretion, which are retained after formation—in particular, due to the presence of reducing moieties. These findings provide physicochemical pathways toward greater control over properties of synthetic catechol-based polymers and adhesives.
Biology offers a valuable inspiration toward the development of self-healing engineering composites and polymers. In particular, chemical level design principles extracted from proteinaceous biopolymers, especially the mussel byssus, provide inspiration for design of autonomous and intrinsic healing in synthetic polymers. The mussel byssus is an acellular tissue comprised of extremely tough protein-based fibers, produced by mussels to secure attachment on rocky surfaces. Threads exhibit self-healing response following an apparent plastic yield event, recovering initial material properties in a time-dependent fashion. Recent biochemical analysis of the structure–function relationships defining this response reveal a key role of sacrificial cross-links based on metal coordination bonds between Zn2+ ions and histidine amino acid residues. Inspired by this example, many research groups have developed self-healing polymeric materials based on histidine (imidazole)–metal chemistry. In this review, we provide a detailed overview of the current understanding of the self-healing mechanism in byssal threads, and an overview of the current state of the art in histidine- and imidazole-based synthetic polymers.
Biotechnology offers an exciting avenue toward the sustainable production of high performance proteinaceous polymeric materials. In particular, the mussel byssus-a high performance adhesive bio-fiber used by mussels to cling on hard surfaces-has become a veritable archetype for bio-inspired self-healing fibers, tough coatings, and versatile wet adhesives. However, successful translation of mussel-inspired design principles into man-made materials hinges upon elucidating structure-function relationships and biological fabrication processes. This review provides a detailed survey of the state-of-the-art understanding of the biochemical structure-function relationships defining byssus performance with a particular focus on structural hierarchy and metal coordination-based cross-linking. The efforts to mimic the byssus in man-made materials are then discussed. While there has been a strong push to mimic the byssus via synthetic chemistry taking a reductionist approach, herein the focus is specifically on recent progress of biotechnology-based strategies that more closely approximate the biochemical complexity of the natural material. As an outlook, an overview of recent research toward understanding the natural byssus assembly process is provided, as processing remains a critical factor in achieving native-like properties.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.