title: Sliding-induced adhesion of stiff polymer microfibre arrays. II. Microscale behaviour.
abstract: The adhesive pads of geckos provide control of normal adhesive force by controlling the applied shear force. This frictional adhesion effect is one of the key principles used for rapid detachment in animals running up vertical surfaces. We developed polypropylene microfibre arrays composed of vertical, 0.3 microm radius fibres with elastic modulus of 1 GPa which show this effect for the first time using a stiff polymer. In the absence of shear forces, these fibres show minimal normal adhesion. However, sliding parallel to the substrate with a spherical probe produces a frictional adhesion effect which is not seen in the flat control. A cantilever model for the fibres and the spherical probe indicates a strong dependence on the initial fibre angle. A novel feature of the microfibre arrays is that adhesion improves with use. Repeated shearing of fibres temporarily increases maximum shear and pull-off forces.
authors.affiliation: Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, CA 94720, USA. bschuber@eecs.berkeley.edu
authors.forename: Bryan
authors.initials: B
authors.lastname: Schubert
authors.forename: Jongho
authors.initials: J
authors.lastname: Lee
authors.forename: Carmel
authors.initials: C
authors.lastname: Majidi
authors.forename: Ronald S
authors.initials: RS
authors.lastname: Fearing
mesh_terms: D000268:Adhesiveness; D000818:Animals; D040761:Biomimetic Materials; D005528:Foot / Q000033:anatomy & histology* / Q000502:physiology; D008116:Lizards / Q000033:anatomy & histology* / Q000502:physiology; D008962:Models, Theoretical; D011126:Polypropylenes / Q000737:chemistry*; D033081:Shear Strength
chemical_list: D011126:Polypropylenes