Complex bio-mechanical systems – The spider fang
Spiders mainly feed on insects. This means that their fangs, which are used to inject venom into the prey, have to puncture the insect cuticle that is essentially made of the same material, a chitin-protein composite, as the fangs themselves.
During the report period a series of fangs of the wandering spider Cupiennius salei were investigated, including texture variation in chitin orientation and arrangement, gradients in protein composition, and selective incorporation of metal ions (Zn and Ca) and halogens (Cl). These modifications influence the mechanical properties of the fang in a graded manner from tip to base, allowing it to perform as a multi-use injection needle that can break through insect cuticle, which is made of a chitin composite as well. The description of the structure and chemistry of the spider fang cuticle, and the identification of the modifications are necessary to adapt an efficient injection needle from nature.
Thin slices of air dried fang samples were prepared with an ultramicrotom. The slices were mounted on lacy-carbon support gold TEM grids and viewed with a HR-TEM/STEM (TITAN 80-300, equipped with EDX and EELS systems) in Z-contrast scanning-transmission mode (HAADF-STEM). These methods allow to analyze the structure, and to a certain extend the composition as well, in the nanometer region, and provided valuable assistance to the related work performed at the Department of Biomaterials of the Max Planck Institute of Colloids and Interfaces in Potsdam.
Figure 1: Micro- and Nanostructure of a spider chelicera (HAADF/STEM image obtained in a TITAN 80-300 electron microscope).