Friction regulation of chiton radulae through the interlocking effect of rigid-flexible structures

The radulae of chitons are chitinous structures that form ribbons bearing tiny denticles used principally to scrape rocky surfaces. Associated teeth have a distinctive interlocking mechanism conferring both flexibility and stiffness to protect the structure against excessive damage caused by high frictional forces. Here we examine the interlocking mechanism and its influence on frictional behavior were examined using numerical modeling and friction tests involving experimental manipulation of the structure. Radulae of the chiton Acanthochitona rubrolineata were compared with those modified to cut the interlocking effect by removing the main lateral teeth (MLT) while leaving the other parts of the structure intact. Results indicate that the interlocking effect significantly enhanced the stiffness of MLT translation/rotation and frictional force through contact constraints from neighboring teeth while substantially reducing the maximum strain of the radulae. The interlocking effect was primarily facilitated by three contact constraints from neighboring second lateral teeth and MLT. The low elastic modulus of the membrane and the connection between MLTs-membrane contribute to the flexibility of the radular structure, which allows for greater freedom of translation/rotation for the loaded MLT, resulting in a strong interlocking effect. This study therefore provides valuable insights into the damage prevention mechanism of a rigid-flexible biological structure under conditions of high friction.