近期,美国科学院院报 (Proceedings of the National Academy of Sciences, 简称PNAS) 发表了上海交通大学自然科学研究院及物理与天文系特别研究员姚振威和美国西北大学的合作者题为“Emergent perversions in the buckling of heterogeneous elastic strips”的论文(113, 7100,2016), 报道了他们在异质复合弹性带领域研究的最新进展。

在生物学上,异质复合弹性带是理解多个尺度范围内生物现象的重要物理模型,包括从细菌中受限染色体形态到植物藤蔓生长等。同时,该模型也是探索螺旋结构中对称破缺的重要工具。在此项研究中,通过耦合具有不同预应变的弹性带,自发产生螺旋结构。并通过控制弹性带两端的取向,在螺旋结构中引入被称为 perversion 的缺陷结构。Perversion 两边的螺旋具有相反的手性。姚振威特别研究员和合作者们系统研究了这些缺陷结构的物理学。模拟和实验发现,perversion 的形成过程,同时也是“凝结”弹性能的过程。Abaqus 模拟结果进一步表明,这些高能态的 perversion 结构之间的相互作用具有互相排斥的性质。通过控制弹性带预应变,计算机模拟观察到相邻 perversion 之间的融合,并最终形成由多个 perversion 均匀排列形成的线性缺陷结构。这些研究结果表明,异质复合弹性带中的 perversion 缺陷结构作为储能元件的可能性,对工程上设计相关柔性器件,包括人造肌肉和柔型机器人等具有一定的指导意义。

Abstract: A perversion in an otherwise uniform helical structure, such as a climbing plant tendril, refers to a kink that connects two helices with opposite chiralities. Such singularity structures are widely seen in natural and artificial mechanical systems, and they provide the fundamental mechanism of helical symmetry breaking. However, it is still not clear how perversions arise in various helical structures and which universal principles govern them. As such, a heterogeneous elastic bistrip system provides an excellent model to address these questions. Here, we investigate intrinsic perversion properties which are independent of strip shapes. This study reveals the rich physics of perversions in the 3D elastic system, including the condensation of strain energy over perversions during their formation, the repulsive nature of the perversion–perversion interaction, and the coalescence of perversions that finally leads to a linear defect structure. This study may have implications for understanding relevant biological motifs and for use of perversions as energy storers in the design of micromuscles and soft robotics.

弹性复合带中 perversion 结构的形成和演化示意图。从图B的相应能量变化中,可以看到 perversion 之间的互相排斥。

参考文献:S. Liu, Z. Yao, K. Chiou, S. I. Stupp, and M. Olvera de la Cruz, “Emergent perversions in the buckling of heterogeneous elastic strips”, Proc. Natl. Acad. Sci. U.S.A. 113, 7100 (2016)