Interdigital interlocking suture: A strong, tough, and flexible biological design

Many animal organs have evolved interlocking sutured structures to achieve superior protective functions while keep excellent flexibility. Interdigital sutures exist widely in animal organs, but the mechanical mechanisms underlying their exceptional properties and functions remain unclear. In this paper, the structure–property interrelation of interdigital sutures is studied through a combination of theoretical, experimental, and numerical efforts. A theoretical model is developed to investigate the strengthening and toughening mechanisms of the sutures. The results are verified by finite element analyses and uniaxial tension tests. The effects of the aspect ratio, interlocking angle, and protrusion length of the sutures on their stiffness, strength, and toughness are revealed. It is found that the higher the interlocking level, the greater the stiffness and strength of the sutures. The toughness first increases and then decreases with the increase in the interlocking level. Our experimental observations show that the optimal geometry of the sutures in Trypoxylus dichotomus can maximize the capability of energy absorption. This study not only deepens our understanding of the mechanical excellence of biological interdigital sutures, but also helps design high-performance biomimetic structures such as engineering joints and protection systems.