Role of Skin Layers on Mechanical Properties and Supercontraction of Spider Dragline Silk Fiber

Abstract

Spider dragline silk is a composite biopolymer that harbors extraordinary mechanical characteristics, and consists of a hierarchically arranged protein core surrounded by outer "skin" layers. However, the contribution of the successive fiber layers on material properties has not been well defined. Here, the influence of the different components on the physicochemical and mechanical properties of dragline is investigated. The crystal structure and the mechanical properties are not changed significantly after the removal of skin constituents, indicating that the core region of dragline silk fibers determines the structural and mechanical properties. Furthermore, the outer layers have little influence on supercontraction, suggesting they do not function as protection against the penetration of water molecules. On the other hand, the outer layers offer some protection against protease digestion. The present study provides insight into how the function and structure of silk fibers are modulated and facilitates the design of silk-inspired functional materials.

Simultaneous effect of strain rate and humidity on the structure and mechanical behavior of spider silk

“…Meanwhile, the dragline silks showed relatively rough fracture surface when the strain rates more than 3.3 × 10 −2 s −1 were applied. The dragline silk consists of a hierarchically arranged protein core surrounded by outer skin layers 25 . The protein core is composed of fibrils that are formed by compact assembly of Fig.…”

Tensegrity Modelling and the High Toughness of Spider Dragline Silk

“…It is generally accepted that the remarkable mechanical performance of spider silk dragline originates from a hierarchical organization of proteins into a hydrogen bonded structure of ordered crystalline β-sheets, embedded in a disordered amorphous matrix [ 1 , 2 , 3 , 4 , 5 , 6 ]. However, at the mesoscale, it has also been shown that silk assembles into nanofibrils with diameters ranging from ~30 nm [ 3 ] to more than 100 nm [ 2 , 5 ] and that a fibre has structurally and functionally distinct regions; a load bearing core (consisting of inner (1800–2300 nm), and outer (300–400 nm) sections [ 2 , 7 , 8 ]) surrounded by protective lipid (10–20 nm), glycol (40–100 nm), and skin (50–100 nm) layers [ 2 ].…”

“…Whilst there have been several concerted modelling efforts to relate silk’s structures to its mechanical properties [ 3 , 4 , 5 , 6 , 7 , 8 , 18 , 19 ], accounting for the precise contributions of each of these structural elements on a fibre’s mechanical response has been inconclusive. Consider, e.g., the role played by the interfaces between the fibrils, which some studies define as mechanically weak and responsible for easy slippage of adjacent fibrils [ 6 ], while other studies observe the presence of heterogeneous protrusions along such surfaces determining a non-slip kinematics and energy dissipation due to interlocking effects [ 20 ].…”

Revealing Spider Silk's 3D Nanostructure Through Low Temperature Plasma Etching and Advanced Low-Voltage SEM

“…In a typical dragline fiber of 5 µm diameter, the coating is approximately 100 nm in thickness and can be further differentiated into a waxy lipids and a glycoprotein layer, which together are attributed with the control of moisture content, antimicrobial properties, and pheromonal communication (Augsten et al, 2000;Sponner et al, 2005Sponner et al, , 2007. Although it is chemically diverse, the contribution of the coating to the fiber's overall tensile behavior has been proposed to be very small (Yazawa et al, 2018). The underlying skin is of similar thickness to the coating and has been found to compose mostly of minor ampullate spidroin protein (MiSp) which is the main component of minor ampullate fibers (Sponner et al, 2007).…”