The Role of Topology and Tissue Mechanics in Remora Attachment
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The Role of Topology and Tissue Mechanics in Remora Attachment Michael Culler1, Keri A. Ledford2 and Jason H. Nadler2 1 Woodruff School of Mechanical Engineering, Georgia Institute of Technology; Atlanta, GA 2 Electro-Optical Systems Laboratory, Georgia Tech Research Institute; Atlanta, GA ABSTRACT Remora fish are capable of fast, reversible and reliable adhesion to a wide variety of both natural and artificial marine hosts through a uniquely evolved dorsal pad. This adhesion is partially attributed to suction, which requires a robust seal between the pad interior and the ambient environment. Understanding the behavior of remora adhesion based on measurable surface parameters and material properties is a critical step when creating artificial, bio-inspired devices. In this work, structural and fluid finite element models (FEM) based on a simplified “unit cell” geometry were developed to predict the behavior of the seal with respect to host/remora surface topology and tissue material properties. INTRODUCTION The remora, of the teleost family Echeneidae, has evolved a unique dorsal pad, whose morphology permits attachment to a wide variety of marine hosts including sharks, sea-turtles, whales, and man-made vessels, despite substantial variations in host topology and flow regimes over the host skin or hull [1]. Remora attachment is unique because it is directional with a strong passive component, meaning that adhesion is enhanced by the maintenance of a viscous drag, or any other posterior-directed shear loading [2]. When external stresses are reversed, the remora can rapidly detach. This suction pad is composed of at least three hierarchical structural features, shown in Figure 1, that contribute to overall attachment performance, and include spinules, a fleshy lip, and lamellar compartments [3]. Fleshy Lip
5mm Lamellar Compartments
2.5mm Spinules
Figure 1: (Left) Photograph of live remora suction pad (photograph courtesy of Brooke Flammang); (Right) Photograph of detached "suction pad" with highlighted structural features of interest This paper focuses on the suction component of attachment contributed by the fleshy lip, and evaluates the role of host topology in limiting attachment. Structural and fluid finite element models (FEM) based on a simplified “unit cell” geometry are developed to predict the behavior of the seal with respect to host surface topology and material properties of the fleshy lip tissue.
Simulations developed in this work may be used in future efforts that seek to design and construct biologically-inspired mechanical attachment systems. THEORY There are two limiting cases for successful remora attachment with respect to host surface topology. In the first case, the host surface is too smooth to create enough “friction” for the remora to resist drag forces resulting from forward locomotion. The second limiting case, which is the focus in this work, occurs when the host surface is so rough that a robust seal cannot be formed due to fluid flow into the pad through a network of channels created
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