Mechanisms of Curing Marine Mussel Adhesives
Marine mussel adhesion is a system that has been of interest in the field of biomimetics due to remarkable properties that have yet to be replicated in synthetic, man-made materials. Development of materials rivaling these biological adhesives has many industrial and everyday consumer applications such as in surgical, construction, and automotive industries. We know that the remarkable strength and underwater properties of these adhesives arise from the presence of 3,4-dihydroxyphenylalanine (DOPA) residues, which exploits unique catechol chemistries to bind to many different types of materials whilst underwater. What remains unknown is the mechanism of how these protein-based materials cure (i.e. cross-link) to produce a solid adhesive material. Such knowledge would greatly advance the development of synthetic adhesives and other catechol-based materials, such as hydrogels. Wilker proposed a mechanism of chemical cross-linking involving the formation of a metal-tris-DOPA complex that undergoes redox reactions to produce an organic radical. This radical is sequestered by oxygen to further cross-link with nearby peptides. This mechanism describes the importance of iron and oxygen to carry out the redox driven cross-linking chemistries. In this work we describe specific implications that iron and oxygen have on the native adhesive materials produced by these mussels. Our in vivo work suggests that iron is used to tune the strength of the materials and oxygen is used to increase extensibility of the native material. These findings are further understood when examined under an electron microscope, where we were able to suggest the structure-function relationships between bulk morphological features and material properties. This study displays the first in vivo evidence for the animal’s use of iron and oxygen to tune the material properties of their underwater adhesives, a material highly mimicked after in man-made materials, and provides potential applications to tune structural and material properties of catechol-based systems.
Wilker, Purdue University.
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