Quasi-static responses of marine mussel plaques detached from deformable wet substrates under directional tensions

Quantifying the response of marine mussel plaque attachment to wet surfaces remains a significant challenge to a mechanistic understanding of plaque adhesion. Here, we develop a novel, customized microscope system, combined with two-dimensional in situ digital image correlation (DIC), to quantify the in-plane deformation of a deformable substrate that interacts with a mussel plaque under directional tension. By examining the strain field within the substrate, we acquired an understanding of the mechanism by which in-plane traction forces are transmitted from the mussel plaque to the underlying substrate. Finite-element (FE) models were developed to assist in the interpretation of the experimental measurement. Our study revealed a synergistic effect of pulling angle and substrate stiffness on plaque detachment, with mussel plaques anchoring to a ‘stiff’ substrate at small pulling angles, i.e. natural anchoring angles, having mechanical advantages with higher load-bearing capacity and less plaque deformation. We identify two distinct failure modes, i.e. shear-traction-governed failure (STGF) and normal-traction-governed failure (NTGF). It was found that increasing the stiffness of the substrate or reducing the pulling angle results in a change of the failure mode from NTGF to STGF. Our findings offer new insights into the mechanistic understanding of mussel plaque–substrate interaction, providing a plaque-inspired strategy to develop high-performance and artificial wet adhesion.