Ashton Nicholas N, Stewart Russell J
Department of Bioengineering, University of Utah, Salt Lake City, Utah 84112, USA.
Soft Matter. 2015 Mar 7;11(9):1667-76. doi: 10.1039/c4sm02435d.
Single fibers of the sticky underwater larval silk of the casemaker caddisfly (H. occidentalis) are viscoelastic, display large strain cycle hysteresis, and self-recover 99% of their initial stiffness and strength within 120 min. Mechanical response to cyclical strains suggested viscoelasticity is due to two independent, self-recovering Ca(2+)-crosslinked networks. The networks display distinct pH dependence. The first network is attributed to Ca(2+)-stabilized phosphoserine motifs in H-fibroin, the second to Ca(2+) complexed carboxylate groups in the N-terminus of H-fibroin and a PEVK-like protein. These assignments were corroborated by IR spectroscopy. The results are consolidated into a multi-network model in which reversible rupture of the Ca(2+)-crosslinked domains at a critical stress results in pseudo-plastic deformation. Slow refolding of the domains results in nearly full recovery of fiber length, stiffness, and strength. The fiber toughening, energy dissipation, and recovery mechanisms, are highly adaptive for the high energy aquatic environment of caddisfly larvae.
石蛾（西方石蛾）水下粘性幼虫丝的单纤维具有粘弹性，表现出大应变循环滞后现象，并在120分钟内自我恢复其初始刚度和强度的99%。对循环应变的机械响应表明，粘弹性是由于两个独立的、自我恢复的Ca(2+)交联网络所致。这些网络表现出不同的pH依赖性。第一个网络归因于H-丝心蛋白中Ca(2+)稳定的磷酸丝氨酸基序，第二个网络归因于H-丝心蛋白N端的Ca(2+)络合羧基和一种类PEVK蛋白。红外光谱证实了这些归属。研究结果整合为一个多网络模型，其中在临界应力下Ca(2+)交联域的可逆破裂导致假塑性变形。这些域的缓慢重折叠导致纤维长度、刚度和强度几乎完全恢复。纤维的增韧、能量耗散和恢复机制，对石蛾幼虫的高能水生环境具有高度适应性。
