Dimensions, Birefringences, and Force-Elongation Behavior of Major and Minor Ampullate Silk Fibers from Orb-Web-Spinning Spiders—The Effects of Wetting on these Properties

Abstract

The effects of wetting by water were determined on the dimensions, birefringences, and force-elongation behavior of major and minor ampullate silk fibers from Araneus diadematus Clerck, and major only from Araneus sericatus Clerck and Araneus gemma (McCook) (all family Araneidae). The values obtained at room conditions (RC), in the wetted, restrained (WR) and wetted, axially unrestrained (WU) states, the ratios of these, between states, are reported upon. The unexpected supercontraction of major ampullate fibers, WU, is contrasted with the stabile behavior of those from the minor ampullate gland systems. When dried from the WR state, both types appear to recover their RC properties. But when dried slack from the WU state, the major ampullate fibers undergo the “drawing” phenomenon typical of many man-made protofibers. The techniques required in order to secure data on these fragile (diameters, 0.6–6.0 μm) fibers, are described in some detail.

Wet webs work better: Humidity, supercontraction and the performance of spider orb webs

“…First, supercontraction of MA silk could prevent orb webs from sagging under the weight of dew drops by keeping the webs tense (Work, 1977). This hypothesis is consistent with the observation that, within Orbiculariae, orb-weaving spiders' silk supercontracts slightly more than silk from taxa that secondarily lost orb-weaving (Boutry and Blackledge, 2010).…”

“…Puthoff et al, 2010;Shawkey et al, 2011). Spider major ampullate (MA) silk is the main structural element in most prey capture webs and responds to humidity over 70% by supercontracting (Work, 1977). During supercontraction, water infiltrates the silk and disrupts the hydrogen bonding that maintains much of the ordered tertiary structure in the amorphous regions of silk proteins (Eles and Michal, 2004;Grubb and Ji, 1999;Parkhe et al, 1997;Termonia, 1994).…”

Strain-dependent fractional molecular diffusion in humid spider silk fibres

“…It appears that some of the adsorbed water is permanently bound [23]. The diameter of major ampullate dragline silk rises from a typical value [31] of (2.8 + 0.5) mm in the dry state to (20.4 + 6.4) mm in the unconstrained fully humid state [31]. When constrained, the diameter of humid silk only reaches a typical value of (9.7 + 3.5) mm [31].…”

The hidden link between supercontraction and mechanical behavior of spider silks

“…Furthermore, spider silk is endowed with a further outstanding feature: the ability to tune its mechanical behavior in a predictable and controllable way (Work, 1976;Denny, 1976;Garrido et al, 2002a,b;Pérez-Rigueiro et al, 2005). Note that as the silk composition is always the same when the spider is tuning the fibers, processing must play a pivotal role in adjusting the final mechanical properties.…”