Instrumentation of biomimetic strain sensors in walking robots

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Locomotion is a crucial component of animal survival that has to be adaptable to be consistently successful. This adaptability is necessary for walking insects to overcome complex and changing terrains in a task-dependent manner. The six legs of insects are coordinated and controlled by local and over-arching networks that control each limb and limb joint, and this modular structure creates necessary flexibility in the system. Locomotor networks consist of pattern-generating interneurons, motor neurons, muscles, and sensory organs. Sensory organs monitor the motor output and provide dynamic modifying and reinforcing feedback onto other network components. Campaniform sensilla (CS), sensory organs found on the majority of limb segments, are analogous to the vertebrates' Golgi tendon organ. CS encode highly dynamic strains that spread through the cuticle. Different strains arise during different behaviors. For example, when a leg switches between its stance and swing phase during walking, the leg is exposed to various strains that change over time. CS on different limbs can monitor these tonic forces and the rate of forces changes over time, and their feedback can modify or reinforce muscular output to ensure coordinated movements and stability.Recently, I used electron microscopy to examine the external morphology of CS. These experiments showed that the number and position of CS varied between individuals and legs. I then used nanocomputed tomography to combine the morphological data with modeling, underscoring the role of the detailed structures of the CS in distributing forces across the cuticle. In a parallel series of experiments, I focused on the neural component of the CS, using optogenetic manipulations to investigate how CS affect leg movements and coordination. In doing so, I demonstrated that small subsets of CS are sufficient and necessary for these behaviors. This underlines the importance of CS for kinematic and temporal coordination of the legs. These findings provide the biological basis for a comprehensive understanding of the function of proprioceptive information in the motor networks of D. melanogaster. The goal of this proposal is to now uncover the mechanical principles of strain measurement and the interplay between biomechanics and nervous systems. My approach integrates the biological CS knowledge with robotic instrumentation to identify relationships between the structure, location, and orientation of sensors in the context of movement behavior. By uncovering the interplay between morphology and strain sensing, this project will reveal how insect sensory structures and neural circuits process the dynamic forces encountered during locomotion. Furthermore, these experiments will fundamentally change our understanding of proprioceptive strain sensing by showing how cuticular structures filter mechanosensory signals.