Abstract
Like marine mussels, freshwater zebra and quagga mussels adhere via the byssus, a proteinaceous attachment apparatus. Attachment to various surfaces allows these invasive mussels to rapidly spread, however the adhesion mechanism is not fully understood. While marine mussel adhesion mechanics has been studied at the individual byssal-strand level, freshwater mussel adhesion has only been characterized through whole-mussel detachment, without direct interspecies comparisons on different substrates. Here, adhesive strength of individual quagga and zebra mussel byssal plaques were measured on smooth substrates with varying hydrophobicity—glass, PVC, and PDMS. With increased hydrophobicity of substrates, adhesive failures occurred more frequently, and mussel adhesion strength decreased. A new failure mode termed 'footprint failure' was identified, where failure appeared to be adhesive macroscopically, but a microscopic residue remained on the surface. Zebra mussels adhered stronger and more frequently on PDMS than quagga mussels. While their adhesion strengths were similar on PVC, there were differences in the failure mode and the plaque-substrate interface ultrastructure. Comparisons with previous marine mussel studies demonstrated that freshwater mussels adhere with comparable strength despite known differences in protein composition. An improved understanding of freshwater mussel adhesion mechanics may help explain spreading dynamics and will be important in developing effective antifouling surfaces.
Highlights
Material properties of the substrates were not characterized[4]
These substrates were selected based on practical considerations: borosilicate glass contains a high amount of silica, polyvinyl chloride (PVC) is a common piping material, and PDMS typically has a low adhesion strength and is often used in antifouling applications[29]
The Ra values were 1.79 ± 0.49 nm, 49.45 ± 4.24 nm, and 23.30 ± 9.11 nm on glass, PVC, and PDMS, respectively, demonstrating that while slight differences exist, the surfaces are all relatively smooth, and mechanical interlock is not expected to play a large role in adhesion
Summary
Material properties of the substrates (e.g. surface roughness, surface energy) were not characterized[4]. While whole mussel detachment tests provide the best measure of the force required to remove the animal from a substrate, it is not possible to directly determine the strength of the plaque-substrate interface from these tests. In order to evaluate differences in the plaque-substrate adhesive interface between zebra and quagga mussel adhesion, single-plaque tensile detachment studies are necessary, as have been performed for marine mussels[8,19,20,21]. The ultrastructure of the plaque-substrate adhesion interface may vary by substrate and species, affecting the attachment strength as a consequence, but this has not yet been investigated. We measured the adhesive strength of individual quagga and zebra mussel byssal plaques on smooth substrates with varying hydrophobicity, namely glass, PVC, and PDMS, in order to understand the contributions of the plaque-substrate interface directly to adhesion. The failure mode was analyzed for the first time at the microscopic level, and the ultrastructure plaque-substrate interface on PVC was examined by TEM
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