Artificial and natural silk materials have high mechanical property variability regardless of sample size

Abstract

Silk fibres attract great interest in materials science for their biological and mechanical properties. Hitherto, the mechanical properties of the silk fibres have been explored mainly by tensile tests, which provide information on their strength, Young’s modulus, strain at break and toughness modulus. Several hypotheses have been based on these data, but the intrinsic and often overlooked variability of natural and artificial silk fibres makes it challenging to identify trends and correlations. In this work, we determined the mechanical properties of Bombyx mori cocoon and degummed silk, native spider silk, and artificial spider silk, and compared them with classical commercial carbon fibres using large sample sizes (from 10 to 100 fibres, in total 200 specimens per fibre type). The results confirm a substantial variability of the mechanical properties of silk fibres compared to commercial carbon fibres, as the relative standard deviation for strength and strain at break is 10–50%. Moreover, the variability does not decrease significantly when the number of tested fibres is increased, which was surprising considering the low variability frequently reported for silk fibres in the literature. Based on this, we prove that tensile testing of 10 fibres per type is representative of a silk fibre population. Finally, we show that the ideal shape of the stress–strain curve for spider silk, characterized by a pronounced exponential stiffening regime, occurs in only 25% of all tested spider silk fibres.

Impact of physio-chemical spinning conditions on the mechanical properties of biomimetic spider silk fibers

“…The fibers with the highest toughness modulus in this experimental series were produced at 29 cm/s, reaching 89 MJ/m 3 (Fig. 5), but they also displayed a large variability, which is typical for silk materials 47 . Because of this, we decided to increase the sample sizes for fibers spun at 29 cm s −1 and 58 cm s −1 (highest toughness and highest strength, respectively).…”

“…Tensile testing. The mechanical properties for each fiber type were determined by tensile testing of 10 to 20 randomly selected fibers from each fiber sample collection 47 . Before tensile testing, each fiber was mounted on a paper frame over a 10 × 10 mm square window and fixed with double-sided tape.…”

Optimized structures for vibration attenuation and sound control in nature: A review

“…In all cases, the sensory capability of an organism benefits from specialized transducers used to detect vibrations (e.g., cuticles for insects and arachnids, silk for spiders). Interestingly, these transducers are often associated with nonlinear constitutive behavior; e.g., both cuticle 191 and silk 192 present a high stiffening behavior with an exponential constitutive law. Moreover, this relationship is strongly mediated by water content, which influences the properties of both the cuticle 141,193 and silk.…”

Magnetostrictive and Electroconductive Stress‐Sensitive Functional Spider Silk

“…The mechanical properties and the diameters of the raw material, ST, are comparable to those reported in the literature and display the same inherent variability. [22,23,26,[39][40][41] The permanence in high vacuum seemed to plasticize the threads by improving their deformability (the strain at break of the VSTs was significantly the highest) whereas the presence of the metallic coating seemed to slightly reduce it. Moreover, the high vacuum stage also seemed to have a marked effect on the mechanical properties of the fibers (strength, especially), as the STs presented the highest strength in comparison to the MSTs and VSTs.…”