Tensile properties of single- and multi-type mixed fibre bundles of spider silk.

Abstract

Spider silk is known for its outstanding toughness at low density, making it a promising model for the biomimetic design of advanced fibre materials. Spiders naturally do not spin single silk fibres but instead produce bundles, or threads, composed of two or more fibres that may originate from the same or different silk glands. Despite their ubiquity, the mechanical properties of these fibre bundles have been largely overlooked. In this study, both naturally spun and forcibly silked fibre bundles from the cosmopolitan cellar spider <i>Pholcus phalangioides</i> (Pholcidae) and naturally spun bundles from the comb-footed cellar spider <i>Nesticus cellulanus</i> (Nesticidae) were examined to test whether post-spinning combinations of different silk materials, such as stiff and soft fibres, enhance the toughness of silk bundles. Despite their compositional diversity, tensile tests showed that the performance of fibre bundles cannot be predicted solely from the properties or the number of the individual fibres. These findings reveal that silk fibre bundles exhibit more complex tensile behaviour than previously recognised and demonstrate that spiders can produce a wide range of mechanical properties through the specific post-processing and combination of silk fibres. This principle of forming heterogeneous bundles may inspire biomimetic approaches to the post-spinning processing of recombinant silks and the design of advanced fibre materials.