Mechanical properties of silk of the Australian golden orb weavers Nephila pilipes and Nephilaplumipes.

Genevieve G Kerr,Joanne Macdonald,Helen F Nahrung,Peter Killen,Aaron Wiegand,Joanna Kristoffersen,Cameron Brown

doi:10.1242/bio.029249

Genevieve G Kerr, Joanne Macdonald + Show 5 more

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https://doi.org/10.1242/bio.029249

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Abstract

ABSTRACTSilks from orb-weaving spiders are exceptionally tough, producing a model polymer for biomimetic fibre development. The mechanical properties of naturally spun silk threads from two species of Australian orb-weavers, Nephila pilipes and Nephila plumipes, were examined here in relation to overall thread diameter, the size and number of fibres within threads, and spider size. N. pilipes, the larger of the two species, had significantly tougher silk with higher strain capacity than its smaller congener, producing threads with average toughness of 150 MJ m−3, despite thread diameter, mean fibre diameter and number of fibres per thread not differing significantly between the two species. Within N. pilipes, smaller silk fibres were produced by larger spiders, yielding tougher threads. In contrast, while spider size was correlated with thread diameter in N. plumipes, there were no clear patterns relating to silk toughness, which suggests that the differences in properties between the silk of the two species arise through differing molecular structure. Our results support previous studies that found that the mechanical properties of silk differ between distantly related spider species, and extends on that work to show that the mechanical and physical properties of silk from more closely related species can also differ remarkably.

Highlights

IntroductionSpider silk is mechanically outstanding: its toughness (amount of energy per unit volume absorbed before rupture) exceeds that of the best synthetic high-performance fibres, including steel and Kevlar (Agnarsson et al, 2010; Guthold et al, 2007; Omenetto and Kaplan, 2010), due to its combination of strength and extensibility (Heim et al, 2009; Rising et al, 2005; Vendrely and Scheibel, 2007; Vollrath and Porter, 2006)
Silk and spider characteristics Female N. pilipes were significantly larger than N. plumipes, but their outer web frame threads did not differ in overall size, nor in individual fibre size or number (Table 1, Fig. 1)
Silk mechanical properties Of the individual threads tested for N. pilipes (n=34 from 12 spiders) and N. plumipes (n=27 from seven spiders), 28% gave invalid results from mechanical failure or fracturing at the attachment site

Summary

Introduction

Spider silk is mechanically outstanding: its toughness (amount of energy per unit volume absorbed before rupture) exceeds that of the best synthetic high-performance fibres, including steel and Kevlar (Agnarsson et al, 2010; Guthold et al, 2007; Omenetto and Kaplan, 2010), due to its combination of strength and extensibility (Heim et al, 2009; Rising et al, 2005; Vendrely and Scheibel, 2007; Vollrath and Porter, 2006). While there are many types of silk, the Major Ampullate (MA) silk produced by orb-weaving spiders is exceptionally strong, extensible and tough, producing silk as tough as 111 MJ m−3 [Nephila clavipes (Linnaeus) – Nephilidae] and 354 MJ m−3 (Caerostris darwini Kuntner and Agnarsson – Araneidae) (Agnarsson et al, 2010). N. pilipes is one of the largest orb-weaving spiders (Su et al, 2007), altering its dragline silk protein in response to variation in prey (Tso et al, 2005), while N. plumipes is a smaller Australian species. Both species are widespread in northeastern and northern coastal Australia, but N. pilipes is genetically divergent from its congeners within Australia (Harvey et al, 2007)

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