Materials World Network: Structural design and micromechanical properties of mechanotransducing biological materials
Experimental Condensed Matter Physics
Final Report Abstract
The lyriform organ located between the last and the second last segments of the leg of the central American wandering spider Cupiennius salei is its most sensitive vibration detector. In addition to its function as a vibration sensor for external stimuli this organ operates as a propriosensor, i.e. a sensor reporting stimuli caused by the spiders own movement. The latter stimuli occur during locomotion, rapid escape and complex movements like those involved in spinning the eggsac or turning around in small crevices. The former stimuli originate from prey, predators and importantly sexual-partners during courtship. The different stimuli are also characterized by different vibration frequencies and amplitude. Locomotive and other proprio-stimuli occur at low frequency and large amplitude (between 0.1 Hz and up to 40 Hz), and external vibration stimuli occur at higher frequencies (above 40 Hz and up to several kilohertz). The sensor is composed of a slit system and a cuticular pad placed just in front of the slits (towards the distal end of the metatarsus), which controls the transmission of the vibrations to the slit organ. We have studied the structure and the mechanical properties of the pad and the slits in order to better understand how they function as a vibration sensor and a filter. Our results show how the different parts of the slit-pad vibration sensory systems are “optimized” in terms of their structure and mechanical properties to allow the filtering and the complex sensory function. We found that the mechanism of high-frequency stimulus transfer (above ca 40 Hz) can be related to the viscoelastic properties of the pad’s most external layer - the epicuticle whereas low-frequency stimuli (less than 40 Hz) transmission is governed by the internal structure and mechanical properties of the pad. For the pad epi-cuticle the transition from glassy material, which can transmit vibration stimulus, to a rubbery material, which is damping the stimulus, occurs at 19 °C. This temperature likely represents the maximum temperature in which the spider spends most of its active hours - the spider is active at night time, when the mountainous area in which it is found cools to 20 °C and slightly below. In addition, the complex overall and sub-structure of the pad not only allow effective stimulus transmission at low frequency but also help to provide mechanical robustness to avoid damage and over compression of the slits by the typical large amplitude of low frequency stimulus. One surprising result was the significantly low modulus value of the distal part of the pad. Such low modulus values (100 MPa) are usually found for joint membranes in insects and arachnids or in the cuticles of larvae. Despite the surprise the structural and the compositional investigation following this observation could fully explain the result and the role of this region in the mechanism of low signal transmission is now clear.
Publications
- A spider’s biological vibration filter: Micromechanical characteristics of a biomaterial surface. (2014) Acta Biomat. 10, 4832-484
S. L. Young, M. Chyasnavichyus, M. Erko, F. G. Barth, P. Fratzl, I. Zlotnikov Y. Politi, V. V. Tsukruk
(See online at https://doi.org/10.1016/j.actbio.2014.07.023) - Micro- and nano-structural details of a spider’s filter for substrate vibrations. Relevance for low frequency signal transmission. (2015) Royal Soc. Interface. 12: 20141111
M. Erko, O. Younus-Metzler, A. Rack, P. Zaslansky, S. Young, G. Milliron, M. Chyasnavichyus, F. G. Barth, P. Fratzl, V. Tsukruk, I. Zlotnikov and Y. Politi
(See online at https://doi.org/10.1098/rsif.2014.1111) - Micromechanical properties of strain-sensitive lyriform organs of a wandering spider (Cupiennius salei). (2016). Acta Biomater. 41, 40-51
S.L. Young, M. Chyasnavichyus, F. G. Barth, I. Zlotnikov, Y. Politi and V. V. Tsukruk
(See online at https://doi.org/10.1016/j.actbio.2016.06.009)
