title: The microscopic network structure of mussel (Mytilus) adhesive plaques.
abstract: Marine mussels of the genus Mytilus live in the hostile intertidal zone, attached to rocks, bio-fouled surfaces and each other via collagen-rich threads ending in adhesive pads, the plaques. Plaques adhere in salty, alkaline seawater, withstanding waves and tidal currents. Each plaque requires a force of several newtons to detach. Although the molecular composition of the plaques has been well studied, a complete understanding of supra-molecular plaque architecture and its role in maintaining adhesive strength remains elusive. Here, electron microscopy and neutron scattering studies of plaques harvested from Mytilus californianus and Mytilus galloprovincialis reveal a complex network structure reminiscent of structural foams. Two characteristic length scales are observed characterizing a dense meshwork (approx. 100 nm) with large interpenetrating pores (approx. 1 µm). The network withstands chemical denaturation, indicating significant cross-linking. Plaques formed at lower temperatures have finer network struts, from which we hypothesize a kinetically controlled formation mechanism. When mussels are induced to create plaques, the resulting structure lacks a well-defined network architecture, showcasing the importance of processing over self-assembly. Together, these new data provide essential insight into plaque structure and formation and set the foundation to understand the role of plaque structure in stress distribution and toughening in natural and biomimetic materials.
authors.affiliation: Materials Research Laboratory, University of California Santa Barbara, Santa Barbara, CA, USA.
authors.forename: Emmanouela
authors.identifier: http://orcid.org/0000-0002-4044-0022
authors.initials: E
authors.lastname: Filippidi
authors.affiliation: Molecular, Cellular and Developmental Biology, University of California Santa Barbara, Santa Barbara, CA, USA.
authors.forename: Daniel G
authors.initials: DG
authors.lastname: DeMartini
authors.affiliation: Chemical Engineering, University of California Santa Barbara, Santa Barbara, CA, USA.
authors.forename: Paula
authors.identifier: http://orcid.org/0000-0002-9911-5320
authors.initials: P
authors.lastname: Malo de Molina
authors.affiliation: Biomolecular Science and Engineering, University of California Santa Barbara, Santa Barbara, CA, USA.
authors.forename: Eric W
authors.identifier: http://orcid.org/0000-0003-4630-1100
authors.initials: EW
authors.lastname: Danner
authors.affiliation: Chemical Engineering, University of California Santa Barbara, Santa Barbara, CA, USA.
authors.forename: Juntae
authors.identifier: http://orcid.org/0000-0002-1319-3521
authors.initials: J
authors.lastname: Kim
authors.affiliation: Chemical Engineering, University of California Santa Barbara, Santa Barbara, CA, USA.
authors.forename: Matthew E
authors.identifier: http://orcid.org/0000-0001-9384-4023
authors.initials: ME
authors.lastname: Helgeson
authors.affiliation: Materials Research Laboratory, University of California Santa Barbara, Santa Barbara, CA, USA Molecular, Cellular and Developmental Biology, University of California Santa Barbara, Santa Barbara, CA, USA Biomolecular Science and Engineering, University of California Santa Barbara, Santa Barbara, CA, USA.
authors.forename: J Herbert
authors.initials: JH
authors.lastname: Waite
authors.affiliation: Materials Research Laboratory, University of California Santa Barbara, Santa Barbara, CA, USA Mechanical Engineering, University of California Santa Barbara, Santa Barbara, CA, USA valentine@engineering.ucsb.edu.
authors.forename: Megan T
authors.identifier: http://orcid.org/0000-0003-4781-8478
authors.initials: MT
authors.lastname: Valentine
mesh_terms: D000825:Animal Structures / Q000737:chemistry / Q000648:ultrastructure*; D000818:Animals; D049878:Mytilus / Q000737:chemistry / Q000648:ultrastructure*
keywords: Mytilus; electron microscopy; mussels; plaques; small-angle neutron scattering