title: Crystal networks in silk fibrous materials: from hierarchical structure to ultra performance.
abstract: This review provides a comprehensive survey of the structural characteristics of crystal networks of silk soft fibrous materials in correlation with the macroscopic properties/performance and the network formation mechanisms. The correlation between the hierarchical mesoscopic structures and the mechanical properties of silk soft fibrous materials including silk fibroin hydrogels and naturally spun silk fibers are addressed based on the hierarchical crystal network models. Namely, two types of hierarchical networks are identified: the weak nanofibril-nanofibril interaction case (i.e., silk fibroin hydrogels), and the strong nanofibril-nanofibril interaction case (i.e., silk fibers). The macroscopic properties, i.e., the rheological/mechanical properties, can be controlled in terms of tuning different levels of hierarchical network structures by ultrasonication-induced gelation, introducing the initial nucleation centers, etc. Such controls take effect by different mesoscale assembly pathways, which are found to occur via different routes of the nucleation and growth processes. Furthermore, the hierarchical network model of soft fibrous materials can be applied to explain the superior mechanical properties and the unique strain-hardening behaviors of spider silk fibers within the framework of hierarchical breaking mechanism. Obviously, a knowledge of crystal networks will allow the prediction of the performance and engineering strategy of silk fibrous materials in generals.
authors.affiliation: Department of Physics, Faculty of Science, National University of Singapore, Singapore, 117542, Singapore; NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore, 117456, Singapore.
authors.forename: Anh Tuan
authors.initials: AT
authors.lastname: Nguyen
authors.forename: Qiao-Ling
authors.initials: QL
authors.lastname: Huang
authors.forename: Zhen
authors.initials: Z
authors.lastname: Yang
authors.forename: Naibo
authors.initials: N
authors.lastname: Lin
authors.forename: Gangqin
authors.initials: G
authors.lastname: Xu
authors.forename: Xiang Yang
authors.initials: XY
authors.lastname: Liu
mesh_terms: D000818:Animals; D012831:Bombyx; D003198:Computer Simulation; D003460:Crystallization; D005349:Fibroins / Q000737:chemistry*; D020100:Hydrogels / Q000737:chemistry; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D057139:Nanofibers / Q000737:chemistry*; D036103:Nanotechnology / Q000379:methods*; D015202:Protein Engineering / Q000379:methods*; D017433:Protein Structure, Secondary; D012212:Rheology; D013112:Spiders; D013314:Stress, Mechanical
chemical_list: D020100:Hydrogels; D005349:Fibroins
keywords: fibers; hierarchical structures; hydrogels; nanofibrils; silks; soft materials