Morphological and confocal laser scanning microscopic investigations of the adductor muscle-shell interface in scallop.

The challenge of joining dissimilar advanced materials has led researchers around the world to search for new and more efficient solutions. This way, we can highlight the muscle-shell attachment in mollusk, which possessed high strength and toughness. In order to make clear how this "bi-material interface" derives its superior mechanical properties, the morphological features of the adductor muscle scar in Patinopecten yessoensis was investigated by means of confocal laser scanning microscopy (CLSM). This scar area was found to consist of a myostracum with many evenly distributed pit structures and a fracture section with a parallel arranged prism-like structure. The measured values of the distribution density, diameter, and depth of those pit structures were 24 ± 4/49,152 μm2, 7.36 ± 2.47 μm, and 1 ± 0.31 μm respectively. Profile of each pit wall was arc curve without closed angle. Furthermore, CLSM micrographs showed that considerable micro pits (0.1-0.9 μm in diameter) distribute round the pit wall and on the pit bottom. This special micromorphology is the first report on the adductor muscle scar in scallop. In addition, the mineral state and mechanical property of the scar surface was analyzed by XRD and nanoindentation test respectively. In general, the study results presented in this work elucidated that the adductor muscle of P. yessoensis was attached to the shell by insertion of collagen fibers and fibril bundles branched from themselves into pits on the myostracum. This specific connection mechanism can increase the strength of the interface without compromising its ductility and toughness.