185. ATTACHMENT DEVICES IN NATURE

Department: Mechanical & Aerospace Engineering
Faculty Advisor(s): Marc A. Meyers | Frank E. Talke

Primary Student
Name: Albert Yu Min Lin
Email: a5lin@ucsd.edu
Phone: 858-534-6091
Grad Year: 2008

Student Collaborators
Ralf Brunner, Rbrunner@talkevax.ucsd.edu | Po-Yu Chen, Pochen@ucsd.edu

Abstract
For the first time a detailed observation of the pedal foot of red abalone Haliotis rufescens reveals the presence of micrometer-scaled setae terminating in nanometer-sized spatulae. Atomic force microscopy (AFM) pull-off force measurements on a single seta performed under various varying humidity conditions indicate contributions from intermolecular and capillary forces. A pull-off force of 424 nN is measured for a single seta at low humidity of 10% on hydrophobic silicon oxide; it is proposed that this is a result of intermolecular forces. An increase to 558 nN at 67% humidity is observed, seemingly due the contribution of capillary forces. These values exceed the theoretical attachment force, 360 nN, for a single seta found using the Johnson, Kendall, and Roberts equation. Using the areal density of setae one can obtain a theoretical attachment stress of 180 kPa. In vivo experiments conducted on live abalone feet in a normal pull-off mode yielded detachment stresses as high as 140 kPa, with a 50% detachment probability of 115 kPa. It is proposed that van der Waals and capillary forces play a role in the attachment mechanism of Haliotis gastropods and effectively enable suction to reach its theoretical limit. These results may lead to improvements in the design of artificial attachment devices.

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