Hydrogel‐Based Method for High‐Resolution Measurements of Contact Mechanics in Rapid Biological Adhesives: A Case Study in Cuttlefish Tentacle Strikes

ABSTRACT

Cuttlefish and squid attach to various substrates in their environment remarkably well using arms and extensible tentacles lined with arrays of suckers. Each sucker has a stiff internal ring with terminal teeth and microstructured rim. Previous studies have measured attachment forces of amputated suckers; however, in vivo investigations are lacking given the short time scales of attachment (milliseconds) and complex array geometries. To address this, we present a novel framework using a cross‐linked and plasticized gelatin hydrogel mimicking the non‐linear mechanical properties of prey tissues, high‐speed videography to locate sucker contact points, and optical coherence tomography for 3D reconstruction of sucker imprints. Comparing in vivo imprints to ex vivo indentations with predefined loads allowed us to correlate imprint shape with normal, contact forces at the sucker rim. We show that cross‐linking significantly increased the relaxation time of the hydrogel, essential for long‐term imprint retention, while plasticization may have reduced self‐healing by interfering with hydrogen‐bond reformation. Such properties enabled observations of sucker attachment in vivo, which indicated that sucker arrays function probabilistically and that aiming and alignment are achieved through large numbers of high‐safety‐factor suckers. Our hydrogel provides a new approach to study biological small‐scale attachment mechanisms in vivo.