Abstract
Spider silks are remarkable materials designed by nature to have extraordinary elasticity. Their elasticity, however, remains poorly understood, as typical stress–strain experiments only allow access to the axial Young’s modulus. In this work, micro-Brillouin light spectroscopy (micro-BLS), a noncontact, nondestructive technique, is utilized to probe the direction-dependent phonon propagation in the Nephila pilipes spider silk and hence solve its full elasticity. To the best of our knowledge, this is the first demonstration on the determination of the anisotropic Young’s moduli, shear moduli, and Poisson’s ratios of a single spider fiber. The axial and lateral Young’s moduli are found to be 20.9 ± 0.8 and 9.2 ± 0.3 GPa, respectively, and the anisotropy of the Young’s moduli further increases upon stretching. In contrast, the shear moduli and Poisson’s ratios exhibit very weak anisotropy and are robust to stretching.
Highlights
Spider silks are remarkable biomaterials with a delicate composition and hierarchical structure that give rise to their high tensile moduli
Based on the direct methods, it has been shown that spider silk is composed of thin skin and many densely packed nanofibrils oriented along the fiber axis.[8,9,12]
We demonstrate the determination of the complete elastic properties of a single spider silk fiber by Brillouin light spectroscopy (BLS) measurements and examine the strain effect on the silk fiber’s elastic properties
Summary
Spider silks are remarkable biomaterials with a delicate composition and hierarchical structure that give rise to their high tensile moduli. The idea behind the more versatile indirect methods (e.g., the stress−strain, AFM three-point bending experiments) originates from the structure−property relations. Based on such experiments, the axial Young’s modulus was obtained and a structural model was proposed to explain the strain-hardening/strain-weakening behaviors of spider silks.[30] despite all the efforts, a satisfactory understanding of the structure of MA silk is still lacking. To gain a more complete understanding, additional elastic properties beyond the axial Young’s modulus available from typical stress−strain measurements are needed. In addition to the local structure relation, the high-frequency (elastic) moduli are related to the intermolecular potential of the system.[39]
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