Author(s)

E. V. Gorb, V. L. Popov & S. N. Gorb

Abstract

Natural hook-and-loop fasteners: anatomy, mechanical properties, and attachment force of the jointed hooks of the Galium aparine fruit E.V. Gorb1, V.L. Popov2 & S.N. Gorb1 Biological Microtribology Group, Division II, MPI of Developmental Biology, Tuebingen, Germany. 2University of Paderborn, FB6 Theoretical Physics, Germany. Abstract Diaspores of many flowering plants are adapted to dispersal by mechanical interlocking to animal fur and feathers. In this study, the attachment force of the fruit hooks of Galium aparine plants is measured using a force tester. It ranges from 9.37 to 44.89 mN (x=23.23, SD=8.13, n=50) and depends on the hook size. Using light and scanning electron microscopy, it is found that the hook consists of two parts, a joint-like base and a hooked cone. The latter originates from the outer layer of the pericarp and may be considered as a modified hollow unicellular trichome. Staining of resin-embedded semithin sections with safranin and fast green shows that the hook wall contains cellulose and lignin. To calculate the Young's modulus, a mathematical model describing the effect of the complex hook geometry was applied. The hooks with and without the base are characterised by different values of the elastic moduli: 2.02 GPa and 23.20 GPa, respectively. Experimental data show that jointed hooks are better adapted to resist forces in different directions compared with non-jointed hooks. This effect is not present in many other plant hooks and is also unknown in industrial hook-and-loop fasteners. 1 Introduction Diaspores (fruits and seeds) of many plant species are adapted to dispersal by attachment to passing animals [ 11. To provide mechanical interlocking to animal fur and feathers, various hooked devices have been evolved on the diaspore surface [2-4]. These structures may posses either several or only one curved part

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