IS THE MOST STRETCHABLE COCOON SILK NANOCOMPOSITE BUNDLE THAT OF THE SPIDER META MENARDI
Abstract
Summary. Spider silks display generally strong mechanical properties, even if differences between species and within the same species can be observed. While many different types of silks have been tested, the mechanical properties of bundles of silk taken from the cocoon of the cave spider Meta menardi have not yet been analyzed. Meta menardi has recently been chosen as the spider of the year 2012, from the European Society of Arachnology. Here we report a study where silk bundles were collected directly from several caves in the north-west of Italy. Field emission scanning electron microscope (FESEM) images showed that bundles are made up of a large number of threads, each of them with diameter of 6.03 ± 0.58 µm. The bundles were strained at the constant rate of 2 mm/min, using a tensile testing machine. The observed maximum stress, strain and toughness modulus, defined as the area under the stress-strain curve, are 0.64 GPa, 751 % and 130.7 MJ/m 3 , respectively. To the best of our knowledge such an observed huge elongation has never been reported for cocoon silk bundles and suggests a “blade of Arianna” mechanism, for preserving the connection with the eggs also under critical detachment conditions. The Weibull statistics was used to analyze the results from mechanical testing, and an average value of Weibull modulus (m) is deduced to be in the range of 1.5 - 1.8 with a Weibull scale parameter (σ0) in the range of 0.33 - 0.41 GPa, showing a high coefficient of correlation (R 2