School of Physical Science and Technology, ShanghaiTech University, 393 Middle Huaxia Road, Shanghai 201210, China.
Shanghai Clinical Research and Trial Center, Shanghai 201210, People's Republic of China.
ACS Nano. 2023 Apr 25;17(8):7662-7673. doi: 10.1021/acsnano.3c00105. Epub 2023 Apr 12.
Animal silk is usually considered to exist as a solid fiber with a highly ordered structure, formed by the hierarchical assembly starting from a single silk fibroin (SF) chain. However, this study showed that silk protein molecules existed in the form of a fractal network structure in aqueous solution, rather than as a single chain. This type of network was relatively rigid with low fractal dimension. Finite element analysis revealed that this network structure significantly helped in the stable storage of SF prior to the spinning process and in the rapid formation of a β-sheeted nanocrystalline and nematic texture during spinning. Further, the strong but brittle mechanical properties of silk could also be well-explained through the fractal network model of silk fibroin. The strength was mainly derived from the dual network structure, consisting of nodes and β-sheet cross-links, whereas the brittleness could be attributed to the rigidity of the SF chains between these nodes and cross-links. In summary, this study presents insights from network topology for understanding the spinning process of natural silk and the structure-property relationship in silk materials.
动物丝通常被认为是以单根丝素（SF）链为起始，通过分级组装形成具有高度有序结构的固态纤维。然而，本研究表明，丝蛋白分子以分形网络结构的形式存在于水溶液中，而不是单链形式。这种网络相对刚性，分形维数较低。有限元分析表明，这种网络结构有助于 SF 在纺丝前稳定储存，并在纺丝过程中迅速形成β-片状纳米晶和向列织构。此外，丝的强但易碎的力学性能也可以通过丝素的分形网络模型得到很好的解释。强度主要来源于由节点和β-片状交联组成的双网络结构，而脆性则归因于这些节点和交联之间 SF 链的刚性。总之，本研究从网络拓扑的角度揭示了天然丝的纺丝过程和丝材料的结构-性能关系。
