DISSERTATION RESEARCH: Mechanics of Soft-bodied Legged Locomotion: Are Caterpillars Worms with Legs?

蠕虫状的身体形状被认为是软体动物最早进化出的身体结构。这种简单的圆柱形通常通过进化进行修改，增加了四肢和其他结构，以改善动物与环境的互动方式。这个项目提出了一个非常基本的问题：这种柔软的附属物是如何改变软体蠕虫状有机体的运动方式的？毛虫，烟草天蛾（Manduca sexta），提供了一个很好的系统来回答这个问题。使用定制的力传感器阵列，研究人员直接测量毛虫腿在正常爬行过程中施加的力。通过将身体的运动与不同方向的力相匹配，可以准确地描述不同的腿如何帮助毛毛虫爬行和攀爬。这项研究还将测量身体压力的变化，以确定毛毛虫与水蛭和蚯蚓等无腿软无脊椎动物的区别。预计由于毛毛虫有腿来锚身体，它将较少依赖于用流体压力使其身体变硬以进行精细的运动控制。这些实验将测试腿是否允许柔软的动物利用其环境中的刚性结构作为不断变化的骨骼。实际上，毛毛虫可以适应它所爬行的形状。了解蠕虫状形态上附属物的功能优势不仅为软材料控制提供了见解，而且还为为什么不同的毛虫有不同数量的腿提供了线索。实际上，这个项目推动了生物力学测量的技术极限。它还将扩大我们对动物运动的理解，并有助于目前的腿系统理论，无论是动物还是机器。可以想象，该项目可以有益于工程和软机器人和设备的开发。

Worm-like body shapes are thought to be some of the earliest evolved body plans for soft moving organisms. This simple cylindrical shape is often modified through evolution with the addition of limbs and other structures to improve how an animal interacts with the environment. This project asks a very fundamental question: how do such soft appendages change the way a soft-bodied worm-like organism moves? The caterpillar, tobacco hornworm (Manduca sexta), offers a great system to answer this question. Using a custom-built force sensor array, the investigators directly measure forces the caterpillar legs exert during normal crawling. By matching the movements of the body to forces in different directions it is possible to accurately describe how different legs help the caterpillar crawl and climb. This study will also measure changes in body pressure to establish how caterpillars differ from non-legged soft invertebrates such as leeches and earthworms. It is expected that because the caterpillar has legs to anchor the body, it will rely less on stiffening its body with fluid pressure for fine movement control. The experiments will test if legs allow soft animals to exploit stiff structures in their environment as a continually changing skeleton. In effect the caterpillar can conform to the shapes that it crawls upon. Understanding the functional benefits of appendages on a worm-like morphology not only provides insights to soft material control, but also gives clues to why different caterpillars have different numbers of legs. Practically, this project pushes the technical limits of biomechanical measurement. It will also expand our understanding of animal locomotion and contribute to current theories of legged systems, both animals and machines. Conceivably, this project can benefit engineering and the development of soft robots and devices.