Can we utilise spider feet for space applications?
Space conditions prohibit the use of fluids for e.g. means of adhesion. Hence reversible adhesion is acquired by (bio inspired) Velcro. For adhesion on various surfaces we intent do mimic the 'dry' adhesion principle employed by spiders and geckos.
Spiders are not insects
Contrary to insects, spiders use a dry adhesive system for attachment to smooth surfaces such as glass of plant leafs. The absence of sticky fluids requires the spiders to employ a different strategy which consists in a fine structural differentiation of the skeleton material into hairs (setae) from which even tinier structures emerge (setules). These setules are brought into close contact with the surface and hence adherer via van der Waals forces. But no matter how strong the attachment is, the spiders easily detach their feet from any surface. This is achieved by an asymmetric design of the setule-tips and different leg kinematics during touch-down and lift-off. While web-living spiders catch their prey by waiting, freely hunting spiders have to literally hunt their prey. Jumping off a smooth surface, catching the prey and subsequently holding on the smooth surface again would not be possible without such an elaborated system of attachment as spiders have developed.
The arthropod cuticle - a fascinating material
The exoskeleton of arthropods, i.e., spiders, insects, etc., is composed of only a few different basic materials. However, by varying parameters such as composition or geometrical organization this material compound can adapt its mechanical properties to a great range of demands. For example, the attachment points of muscles need to be very tough, while joints need to be as flexible as possible. The surface of the body, and especially lightweight structures such as wings need to remain free of dust and therefore show particle repellency. On the other hand the feet need to establish safe and removable attachments to smooth surfaces. All these and many other features are achieved with a material continuum that can change its properties within a few micrometers.
During my studies in Saarbrücken, I mainly focussed on the characterization of the cuticle’s properties using the atomic force microscope (AFM). But in other (unpublished) studies we employed methods such as strain measurements and high resolution NMR.
Experiments included:
- Adhesion measurement on single attachment hairs of spider tarsi
- Indentation measurements on tick opistosoma
- Indentation measurements on passive conveying systems of the wings of May bugs
- Microstructure of particle repellent coverings on insect wing membranes
- Geometry of folded beetle-wings
