Plant Biomechanics Group @ Botanic Garden, University of Freiburg, Freiburg, Germany; Freiburg Center for Interactive Materials and Bioinspired Technologies (FIT), Freiburg, Germany; Freiburg Materials Research Center (FMF), Freiburg, Germany; Cluster of Excellence livMatS @ FIT - Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, Germany.
Plant Biomechanics Group @ Botanic Garden, University of Freiburg, Freiburg, Germany; Freiburg Center for Interactive Materials and Bioinspired Technologies (FIT), Freiburg, Germany; Freiburg Materials Research Center (FMF), Freiburg, Germany.
Acta Biomater. 2024 Nov;189:478-490. doi: 10.1016/j.actbio.2024.10.002. Epub 2024 Oct 10.
Tendrils of climbing plants possess a striking spring-like structure characterized by a minimum of two helices of opposite handedness connected by a perversion. By performing tensile experiments and morphological measurements on tendrils of the climbing passion flower Passiflora discophora, we show that these tendril springs act as coil springs within the plant's attachment system and resemble technical coil springs. However, tendril springs have a low spring index and a high pitch angle compared with typical metal coil springs resulting in a more complex loading situation in the plant tendrils. Moreover, the tendrils undergo a drastic shift from the fresh turgescent stage to a dried-off and dead senescent stage. This entails changes in material properties (elastic modulus in tension), morphology (tendril and helix diameter, number of windings), anatomy (tissue composition), and failure behavior (susceptibility to delamination) and reduces the degree of elasticity and strain at failure of the tendrils. Nevertheless, senescent tendrils remain functional as springs and maintain high energy dissipation capacity and high break force. This renders the system highly energy efficient, as the plant no longer needs to metabolically sustain the died-back tendrils. Because of its energy-storing spring system, its high energy dissipation and high safety factor, the attachment system can be considered a 'fail-safe' system. STATEMENT OF SIGNIFICANCE: The use of coil springs as mechanical devices is not restricted to man-made machinery; striking spring structures can also be found within the attachment systems of climbing plants. Passiflora discophora climbs by using long thin tendrils with adhesive pads at their tips. Once the pads have attached to a support, the tendrils coil and form a spring-like structure. Here, we analyze the form and mechanics of these 'tendril springs', compare them with conventional technical coil springs, and discuss changes in the tendril springs during plant development. We reveal the main features of the attachment system, which might inspire new artificial attachment devices within the emerging field of plant-inspired soft-robotics.
攀援植物的卷须具有一种引人注目的弹簧状结构，其特征是由两个旋向相反的螺旋通过扭曲连接而成。通过对攀援西番莲 Passiflora discophora 的卷须进行拉伸实验和形态测量，我们表明这些卷须弹簧在植物的附着系统中充当螺旋弹簧，类似于技术螺旋弹簧。然而，与典型的金属螺旋弹簧相比，卷须弹簧的弹簧指数较低，螺距角较高，导致植物卷须中的加载情况更为复杂。此外，卷须经历了从新鲜多汁的幼嫩阶段到干燥死亡的衰老阶段的剧烈转变。这导致了材料性能（拉伸弹性模量）、形态（卷须和螺旋直径、匝数）、解剖结构（组织组成）和失效行为（分层倾向）的变化，并降低了卷须的弹性和失效应变程度。尽管如此，衰老的卷须仍然作为弹簧保持功能，并保持高能量耗散能力和高断裂力。这使得该系统具有很高的能量效率，因为植物不再需要代谢维持已经死亡的卷须。由于其储能弹簧系统、高能量耗散和高安全系数，附着系统可以被认为是一种“失效安全”系统。意义陈述：螺旋弹簧作为机械装置的使用不仅限于人造机械；在攀援植物的附着系统中也可以发现引人注目的弹簧结构。Passiflora discophora 通过使用带有粘性垫的长而细的卷须来攀爬。一旦垫子附着在支撑物上，卷须就会卷曲并形成弹簧状结构。在这里，我们分析了这些“卷须弹簧”的形式和力学特性，将它们与传统的技术螺旋弹簧进行了比较，并讨论了植物发育过程中卷须弹簧的变化。我们揭示了附着系统的主要特点，这可能会为新兴的植物启发型软机器人领域中的新型人工附着装置提供灵感。
