Sucker Rings from the Humboldt Squid Dosidicus gigas: The Role of Nanotubule Architecture on the Mechanical Properties
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Sucker Rings from the Humboldt Squid Dosidicus gigas: The Role of Nanotubule Architecture on the Mechanical Properties Ali Miserez1, James C. Weaver2, David Kisailus2 and Henrik Birkedal3 1 , Materials Department and Marine Science Institute, University of California, Santa Barbara, CA-93106, USA 2 Department of Chemical and Environmental Engineering University of California, Riverside, CA-92521, USA 3 Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO), 140 Langelandsgade, Aarhus University, DK-8000 Århus, Denmark
ABSTRACT The suckers that line the arms and tentacles of squid are equipped with rigid toothed ringlike elements that increase the gripping power during prey capture and handling. The sucker rings of the Humboldt squid Dosidicus gigas, are fully proteinaceous and contain nanotubules with diameters ranging from 100 to 250 nm. It has been shown previously that the ensuing porosity is a prime determinant of the local elastic modulus [A. Miserez et al., Adv. Mater. 21, 401 (2009)]. Here additional nanoindentation data are presented together with structural analyses. The nanomechanical data support our model that the measured modulus is determined by the local porosity. The dry moduli reach ca. 8 GPa and are reduced about two-fold in the hydrated state. This surprisingly small reduction is discussed in relation to possible chemistries responsible for assembly of these structures. INTRODUCTION The cephalopods, which include squid and octopi, grasp onto objects through the action of muscularized suckers regularly placed along their tentacles and arms. Despite these similarities in prey capture strategies, the design of squid and octopi suckers differ significantly from each other: While the suckers of octopi rely exclusively on the suction power generated by muscular contraction and the conforming nature of the flexible outer margin [1], squid suckers are mounted on flexible stalks and are equipped with additional rigid toothed ring-like elements [2] as illustrated in Figure 1A and 1B. We recently showed that the sucker rings of the up to 2 m long red devil or Humboldt squid, Dosidicus gigas, contain parallel tubular elements with diameters in the 100-250 nm range [3]. In addition to this unusual microstructure, the sucker rings were shown to be proteinaceous and devoid of chitin. They were also found to be noncrystalline and contain, in addition to their organic constituents, only sulfur and chlorine (as determined by the detection limits of energy dispersive spectroscopy) [3]. Here we review our previous results and provide new data on the local mechanical properties as probed by nanoindentation and speculate on the underlying chemistry responsible for these observations. EXPERIMENT The sucker rings used in this study were isolated from Humboldt squid collected from Hueneme Canyon (N 34.06, W 119.16) during May to July, 2007 at 110-183 m depths [3]. The
sucker rings were isolated from 10 individuals and the residual salt was removed by soaking them overnight in deionized w
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