Uncoiling springs promote mechanical functionality of spider cribellate silk

Abstract

Composites, both natural and synthetic, achieve novel functionality by combining two or more constituent materials. For example, the earliest adhesive silk in spider webs – cribellate silk – is composed of stiff axial fibers and coiled fibers surrounded by hundreds of sticky cribellate nanofibrils. Yet little is known of how fiber types interact to enable capture of insect prey with cribellate silk. To understand the roles of each constituent fiber during prey capture, we compared the tensile performance of native-state and manipulated threads produced by Psechrus clavis, and the adhesion of native threads along a smooth surface and hairy bee thorax. We found that the coiled fiber increases the work to fracture of the entire cribellate thread by up to 20-fold. We also found that the axial fiber breaks multiple times during deformation, an unexpected observation that indicates: i) the axial fiber continues to contribute work even after breakage, ii) the cribellate nanofibrils may perform a previously unidentified role as a binder material that distributes forces throughout the thread. Work of adhesion increased on surfaces with more surface structures (hairy bee thorax) corresponding to increased deformation of the coiled fiber. Together, our observations highlight how the synergistic interactions among the constituents of this natural composite adhesive enhance functionality. These highly extensible threads may serve to expose additional cribellate nanofibrils to form attachment points with prey substrata while also immobilizing prey as they sink into the web due to gravity.

Ambient Climate Influences Anti-Adhesion between Biomimetic Structured Foil and Nanofibers

“…These so-called cribellate spiders produce thousands of nanofibers as adhesive parts of their capture threads (Figure 1a,b). The 10 to 30 nm thick nanofibers are wrapped around supporting axial fibers and, depending on the species, further silk types can be involved, influencing the mechanical properties of the thread [12][13][14][15][16][17]. The spiders extract the nanofibers from spigots of the eponymous cribellum, a spinning plate on the abdomen of cribellate spiders [18,19].…”

Spidroin profiling of cribellate spiders provides insight into the evolution of spider prey capture strategies

“…The cribellate capture threads are composed of materials with different mechanical properties, the core fibre is stiff, and the cribellate nanofibrils is extensible 23 . This composite has a synergistic mechanical function that the core fibres are broken intermittently at the early stage of tensile deformation, and the threads gradually unravel and elongate to increase thread extension 24 . The cribellate capture threads are dry and, rather than adhering to prey, entangle prey 25 – 27 .…”

Cribellate thread production as model for spider’s spinneret kinematics

“…The cribellate spinning process is a rhythmical interplay of different spatio-temporal factors leading to a combination of cribellate, axial, and possibly other fibres, such as undulating and supporting fibres (Peters 1984 ; Joel et al 2015 ; Grannemann et al 2019 ; Michalik et al 2019 ;). This combination of different types of silk affects the mechanical properties of a cribellate capture thread (Michalik et al 2019 ; Piorkowski et al 2020 ). The spinning sequence is highly conserved, not only in B. longinqua but also in other cribellate spiders, such as Uloborus plumipes or Kukulcania hibernalis (Joel et al 2015 , 2016, Grannemann et al 2019 ).…”

“…The online version of this article (https ://doi.org/10.1007/s0035 9-020-01460 -4) contains supplementary material, which is available to authorized users. silks, comparable to a fibre-composite (Michalik et al 2019;Piorkowski et al 2020).…”

“…Up to six different types of silk, including thousands of nanofibres (Ø 10–30 nm) and several larger fibres, are connected to complex three-dimensional structures (Peters 1992 ; Eberhard and Pereira 1993 ; Opell 2002 ; Joel et al 2015 ; Grannemann et al 2019 ). The use of different fibres influences the mechanical properties of the capture threads beyond the molecular properties of their individual silks, comparable to a fibre-composite (Michalik et al 2019 ; Piorkowski et al 2020 ).…”