Nanomechanics of new materials — AFM and computer modelling studies of trichoptera silk

Abstract

Abstract:Caddisfly (Trichopera) can glue diverse material underwater with a silk fiber. This makes it a particularly interesting subject for biomimetcs. Better understanding of silk composition and structure could lead to an adhesive capable to close bleeding wounds or to new biomaterials. However, while spiderweb or silkworm secretion is well researched, caddisfly silk is still poorly understood. Here we report a first nanomechanical analysis of H. Angustipennis caddisfly silk fiber. An Atomic Force Microscope (AFM) imaging shows dense 150 nm bumps on silk surface, which can be identified as one of features responsible for its outstanding adhesive properties. AFM force spectroscopy at the fiber surface showed, among others, characteristic saw like pattern. This pattern is attributed to sacrificial bond stretching and enhances energy dissipation in mechanical deformation. Similarities of some force curves observed on Tegenaria domestica spiderweb and caddisfly silk are also discussed. Steered Molecular Dynamics simulations revealed that the strength of short components of Fib-H HA species molecules, abundant in Trichoptera silk is critically dependent on calcium presence.

Peroxinectin catalyzed dityrosine crosslinking in the adhesive underwater silk of a casemaker caddisfly larvae, Hysperophylax occidentalis

“…The (pSX) n motifs comprise about 30% of the H-fibroin sequence. Ionic Ca 2þ /phosphate interactions stabilize the H-bonded (pSX) n b-domains in the aqueous niche, and are responsible for the stiffness, tensile strength, and energydissipating qualities of the fibers (Ashton et al, 2013a;Strzelecki et al, 2011). Likewise, the primary sequence homology between silkworm and caddisfly L-fibroins is low, <25% overall identity (Yonemura et al, 2009).…”

β-Sheet Nanocrystalline Domains Formed from Phosphorylated Serine-Rich Motifs in Caddisfly Larval Silk: A Solid State NMR and XRD Study

“…23,24 Computer modeling of the motif of interest also identified a significant boost in strength when the serines are phosphorylated and when calcium cations are present. 25 The introduction of calcium to multi-phosphorylated peptides has been previously shown to induce β-sheet conformations; this mechanism may be relevant to the formation of neurofilament tangles in Alzheimer’s disease patients. 26–28 In caddisfly silk, this molecular arrangement possibly serves as a structural replacement for sheet-forming poly(A) and poly(GA) repeats in spider and silkworm silks.…”

Silk tape nanostructure and silk gland anatomy of trichoptera

“…40 However, the presence of divalent Ca 21 ions could stabilize (pSX) 4 b-sheets. 25 Further, Ca 21 could promote stacking of the b-sheets into semicrystalline domains ( Figure 12B). Formation of the silk fiber, in this model, would be highly dependent on the local pH and Ca 21 concentration within the lumen, which would provide a biochemical trigger mechanism and driving force for large-scale structural reorganization of silk fiber precursors.…”