Minor Ampullate Silks from Nephila and Argiope Spiders: Tensile Properties and Microstructural Characterization

Abstract

The mechanical behavior and microstructure of minor ampullate gland silk (miS) of two orb-web spinning species, Argiope trifasciata and Nephila inaurata, were extensively characterized, enabling detailed comparison with other silks. The similarities and differences exhibited by miS when compared with the intensively studied major ampullate gland silk (MAS) and silkworm (Bombyx mori) silk offer a genuine opportunity for testing some of the hypotheses proposed to correlate microstructure and tensile properties in silk. In this work, we show that miSs of different species show similar properties, even when fibers spun by spiders that diverged over 100 million years are compared. The tensile properties of miS are comparable to those of MAS when tested in air, significantly in terms of work to fracture, but differ considerably when tested in water. In particular, miS does not show a supercontraction effect and an associated ground state. In this regard, the behavior of miS in water is similar to that of B. mori silk, and it is shown that the initial elastic modulus of both fibers can be explained using a common model. Intriguingly, the microstructural parameters measured in miS are comparable to those of MAS and considerably different from those found in B. mori. This fact suggests that some critical microstructural information is still missing in our description of silks, and our results suggest that the hydrophilicity of the lateral groups or the large scale organization of the sequences might be routes worth exploring.

Structural hysteresis in dragline spider silks induced by supercontraction: an X-ray fiber micro-diffraction study

“…25,42,43,44 Tensile properties of MA silks are affected significantly more than the MiA silks, due to the plasticizing effect of water during supercontraction, with a significant reduction in the initial elastic modulus in MA silks. 15,26,28 …”

“…Extent of supercontraction is defined in this paper (in accordance with previous works 19,28 ) as ( L 0 − L c )/L 0 , where L 0 is the original dry native state length of the fiber and L c the length of the supercontracted/contracted unrestrained fiber.…”

Tuning the instrument: sonic properties in the spider's web

“…Interface 13: 20160341 supercontraction in their webs could be controlled by actively altering radial thread tension during or after web building [18 -20], as well as co-spinning minor ampullate silk during web building. Minor ampullate silk is often co-spun with major ampullate and does not supercontract [44], but its biological role in webs is still unclear [54,55]. It could have a role in controlling the extent of supercontraction of major ampullate threads, as minor ampullate is often seen to be 10% longer than their co-spun counterparts, which suggests that 'supercontraction stress' can also create slack in minor ampullate threads [50].…”

Duplication and concerted evolution of MiSp-encoding genes underlie the material properties of minor ampullate silks of cobweb weaving spiders

“…Additionally, minor and major ampullate silks display different physical properties when wet. Supercontraction in water occurs with A. trifasciata and Nephila inaurata major ampullate silks, which allows them to become more extensible while maintaining their high strength [13]. However, when minor ampullate silks from the same species are exposed to water, supercontraction does not occur and the mechanical properties do not change [13].…”