Hierarchical Structure of Silk Materials Versus Mechanical Performance and Mesoscopic Engineering Principles

Abstract

A comprehensive review on the five levels of hierarchical structures of silk materials and the correlation with macroscopic properties/performance of the silk materials, that is, the toughness, strain‐stiffening, etc., is presented. It follows that the crystalline binding force turns out to be very important in the stabilization of silk materials, while the β‐crystallite networks or nanofibrils and the interactions among helical nanofibrils are two of the most essential structural elements, which to a large extent determine the macroscopic performance of various forms of silk materials. In this context, the characteristic structural factors such as the orientation, size, and density of β‐crystallites are very crucial. It is revealed that the formation of these structural elements is mainly controlled by the intermolecular nucleation of β‐crystallites. Consequently, the rational design and reconstruction of silk materials can be implemented by controlling the molecular nucleation via applying sheering force and seeding (i.e., with carbon nanotubes). In general, the knowledge of the correlation between hierarchical structures and performance provides an understanding of the structural reasons behind the fascinating behaviors of silk materials.

High Carbonization Temperature to Trigger Enzyme Mimicking Activities of Silk‐Derived Nanosheets

“…Thus, the SF solution was obtained by removing the sericin proteins to deconstruct the hierarchical structure of silk fibers. [ 29 ] Then, N‐rich CSFs were prepared through facile one‐step carbonization of the lyophilized SF process. Typically, CSF carbonized at 900 °C with a heating rate of 2 °C min −1 under argon atmosphere was synthesized, and named CSF‐900.…”

Formation, Structure, and Mechanical Performance of Silk Nanofibrils Produced by Heat‐Induced Self‐Assembly

“…These well‐organized hierarchical arrangements of nanoscale fibrils, forming central features in sophisticated structures, contribute highly to the mechanical performance and functions of biologically originating animal silks. [ 1–8 ] SNFs generally show bead‐like structure, comprising of alternating β‐sheet nanocrystals and amorphous regions. Mechanically, the amorphous regions govern the elasticity of silks, whereas β‐sheet nanocrystals play essential roles in tradeoff between modulus, strength, and toughness.…”

“…[ 24 ] Hence, it shows inherent tendency to assemble into supramolecular structures. [ 7 ] The self‐assembly processes of SF can be triggered and accelerated by external stimuli, such as electric fields, pH, ions, mechanical shear, ultrasound, heat, and ethanol treatment, which can induce the transition in conformation of SF. [ 16–23 ] Among them, heat‐induced self‐assembly (HISA) process has been developed to produce water dispersed SNF solutions, due to its advantages, such as accessibility, scalability, and environmental friendliness.…”

Redesigned Silk: A New Macroporous Biomaterial Platform for Antimicrobial Dermal Patches with Unique Exudate Wicking Ability

“…Silk is characterized by a precise coaxial structuration of two proteins, a silk fibroin (SF) core and a silk sericin (SS) sheath that envelopes the former. Similarly to bone, skin or wood, silk's extraordinary macroscopic mechanical performance correlates positively with the mesoscopic hierarchical structure of its fibers [11] . Five levels of structural hierarchy have been identified in silk [14]: (level 1) amino acid sequence within the protein molecules; (level 2) secondary structure (regular hydrogen bonding pattern between the amine and carboxyl groups yielding -helices, -sheets and -turns); (level 3) intermolecular βcrystallites; (level 4) molecular -crystal network (nanofibrils [12] ), in which amorphous chains bond the crystallites together along a nano-fishnet topology; and (level 5) nanofibrils network (multi-domain system).…”

“…Five levels of structural hierarchy have been identified in silk [14]: (level 1) amino acid sequence within the protein molecules; (level 2) secondary structure (regular hydrogen bonding pattern between the amine and carboxyl groups yielding -helices, -sheets and -turns); (level 3) intermolecular βcrystallites; (level 4) molecular -crystal network (nanofibrils [12] ), in which amorphous chains bond the crystallites together along a nano-fishnet topology; and (level 5) nanofibrils network (multi-domain system). It has been claimed that the outstanding mechanical properties of silk materials, originate from the nano-fishnet topology structure of the β-crystallites in the molecular-scale crystal networks, and from the strong friction among nanofibrils in the mesoscopic nanofibrils network [11] . Silk also holds attractive environmental credentials, such as biodegradability, and sustainable and ecological production.…”