title: Determination of the Young's modulus of the epicuticle of the smooth adhesive organs of Carausius morosus using tensile testing.
abstract: Adhesive organs like arolia of insects allow these animals to climb on different substrates by creating high adhesion forces. According to the Dahlquist criterion, adhesive organs must be very soft, exhibiting an effective Young's modulus of below 100 kPa to adhere well to substrates. Such a low effective Young's modulus allows the adhesive organs to make almost direct contact with the substrate and results in van der Waals forces along with capillary forces. In previous studies, the effective Young's moduli of adhesive organs were determined using indentation tests, revealing their structure to be very soft. However, adhesive organs show a layered structure, thus the measured values comprise the effective Young's moduli of several layers of the adhesive organs. In this study, a new approach is illustrated to measure the Young's modulus of the outermost layer of the arolium, i.e. of the epicuticle, of the stick insect Carausius morosus. As a result of the epicuticle being supported by upright fibres, tensile tests allow the determination of the Young's modulus of the epicuticle with hardly influence from subjacent layers. In our tensile tests, arolia of stick insects adhering on a latex membrane were stretched by stretching the membrane while the elongation of the contact area between an arolium and the membrane was recorded. For analysis, mathematical models of the mechanical system were developed. When fed with the observed elongations, these models yield estimates for the Young's modulus of the epicuticle of approximately 100 MPa. Thus, in arolia, a very thin layer (~225 nm) of a rather stiff material, which is less susceptible to abrasion, makes contact with the substrates, whereas the inner fibrous structure of arolia is responsible for their softness.
authors.affiliation: Department Cellular Neurobionics, Institute for Biology II, RWTH Aachen University, Worringerweg 3, 52074 Aachen, Germany Westfälisches Institut für Bionik, Westfälische Hochschule Gelsenkirchen Bocholt Recklinghausen, Münsterstraße 265, 46397 Bocholt, Germany michael.bennemann@w-hs.de.
authors.forename: Michael
authors.initials: M
authors.lastname: Bennemann
authors.affiliation: Department Cellular Neurobionics, Institute for Biology II, RWTH Aachen University, Worringerweg 3, 52074 Aachen, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Backhaus
authors.affiliation: Department Cellular Neurobionics, Institute for Biology II, RWTH Aachen University, Worringerweg 3, 52074 Aachen, Germany.
authors.forename: Ingo
authors.initials: I
authors.lastname: Scholz
authors.affiliation: Central Facility for Electron Microscopy, RWTH Aachen University, Ahornstraße 55, 52074 Aachen, Germany.
authors.forename: Daesung
authors.initials: D
authors.lastname: Park
authors.affiliation: Central Facility for Electron Microscopy, RWTH Aachen University, Ahornstraße 55, 52074 Aachen, Germany.
authors.forename: Joachim
authors.initials: J
authors.lastname: Mayer
authors.affiliation: Department Cellular Neurobionics, Institute for Biology II, RWTH Aachen University, Worringerweg 3, 52074 Aachen, Germany Institute of Biomedical Mechatronics, University of Linz, Altenbergerstraße 69, 4040 Linz, Austria.
authors.forename: Werner
authors.initials: W
authors.lastname: Baumgartner
mesh_terms: D000268:Adhesiveness; D000818:Animals; D001696:Biomechanical Phenomena; D055119:Elastic Modulus; D005121:Extremities / Q000033:anatomy & histology* / Q000502:physiology; D006244:Hardness; D007313:Insecta / Q000502:physiology / Q000648:ultrastructure*; D013499:Surface Properties; D013718:Tensile Strength
keywords: Adhesion; Arolium; Carausius morosus; Cuticle; Finite element simulation; Stick insects