Elasticity Anisotropy of <i>Bombyx mori</i> Silkworm Silk Fiber by Brillouin Light Spectroscopy

Silkworm silk has long been an important natural protein fiber for textile and medical applications, where its superior mechanical properties play a crucial role. Despite the many studies by conventional stress-strain tests, our understanding of the mechanical properties of silkworm silk remains limited. This work investigates the complete elastic properties of <i>Bombyx mori</i> silkworm silk in a noncontact, noninvasive manner by conducting Brillouin light spectroscopy experiments. The analysis of the angle-dependent sound velocities leads to the determination of the full elastic tensor and the engineering mechanical properties of the silkworm silk in natural and stretched states. In the natural state, the axial and lateral Young's moduli are 23.4 ± 1.0 and 10.4 ± 0.5 GPa, respectively, giving an elastic anisotropy of 2.3. Different from the strain-hardening behavior of the spider silk, the mechanical properties of the silkworm silk exhibit a weak strain-dependence up to the breakage strain (∼20%).