Department of Mechanical Engineering, University of California, Santa Barbara, CA 93106, USA.
Biomolecular Science and Engineering Graduate Program, University of California, Santa Barbara, CA 93106, USA.
J R Soc Interface. 2022 Mar;19(188):20210828. doi: 10.1098/rsif.2021.0828. Epub 2022 Mar 23.
Mussels use byssal threads to secure themselves to rocks and as shock absorbers during cyclic loading from wave motion. Byssal threads combine high strength and toughness with extensibility of nearly 200%. Researchers attribute tensile properties of byssal threads to their elaborate multi-domain collagenous protein cores. Because the elastic properties have been previously scrutinized, we instead examined byssal thread viscoelastic behaviour, which is essential for withstanding cyclic loading. By targeting protein domains in the collagenous core via chemical treatments, stress relaxation experiments provided insights on domain contributions and were coupled with small-angle X-ray scattering to investigate relaxation-specific molecular reorganizations. Results show that when silk-like domains in the core were disrupted, the stress relaxation of the threads decreased by nearly 50% and lateral molecular spacing also decreased, suggesting that these domains are essential for energy dissipation and assume a compressed molecular rearrangement when disrupted. A generalized Maxwell model was developed to describe the stress relaxation response. The model predicts that maximal damping (energy dissipation) occurs at around 0.1 Hz which closely resembles the wave frequency along the California coast and implies that these materials may be well adapted to the cyclic loading of the ambient conditions.
贻贝利用足丝将自己固定在岩石上，并在波浪运动产生的周期性负荷下作为减震器。足丝具有高强度、高韧性和近 200%的可拉伸性。研究人员将足丝的拉伸性能归因于其精细的多域胶原蛋白核心。由于弹性特性已经过先前的仔细研究，因此我们转而研究足丝的粘弹性行为，这对于承受周期性负荷至关重要。通过针对胶原蛋白核心中的蛋白质域进行化学处理，应力松弛实验提供了关于域贡献的见解，并与小角 X 射线散射相结合，以研究特定于松弛的分子重排。结果表明，当核心中的类丝域被破坏时，线程的应力松弛几乎降低了 50%，并且横向分子间距也降低了，这表明这些域对于能量耗散是必不可少的，并且在被破坏时会发生压缩分子重排。开发了一个广义的 Maxwell 模型来描述应力松弛响应。该模型预测最大阻尼（能量耗散）发生在大约 0.1 Hz 左右，这与加利福尼亚海岸的波浪频率非常接近，这意味着这些材料可能非常适合环境条件的周期性负荷。
