Hard and soft materials form a fatigue-resistant fan in the mussel’s hinge

How does a mussel shell open and shut easily and without damage for hundreds of thousands of cycles during the bivalve’s lifetime? Such fatigue-resistant materials would be useful in electronics, aerospace and tissue engineering designs, where components need to operate repeatedly without failure. Xiang-Sen Meng and colleagues took a closer look at the hinge on the shell of the bivalve Cristaria plicata, and found that the answer lies in a combination of design and materials that resist brittle fracture over time. Microscopic observations by Meng et al. show that the hinge gets its unique properties through a structure that resembles a folding fan, with biomineralized aragonite nanowires making up the ribs of the fan, and a softer organic matrix as the folds. The nanowires provide rigidity and help distribute stresses toward the circumference of the hinge, and are strengthened by twinning planes that develop in aragonite crystals. The soft matrix absorbs compressive and shear stresses as the valve opens and closes. The researchers developed a proof-of-concept artificial version of the hinge by embedding glass fibers in a matrix of polydimethylsiloxane polymer. Rachel Crane and Mark Denny discuss the findings in a related Perspective.