Meeting Abstract

P1.142  Monday, Jan. 4  Variable gearing in artificial pneumatic “muscles” CRYNES, GL*; AZIZI, E; ROBERTS, TJ; Brown University; Brown University; Brown University gavin_crynes@brown.edu

In pinnate muscles, fibers are oriented at an angle to the muscle’s line of action and rotate as they shorten, becoming more oblique throughout a contraction. This change in fiber orientation decouples the shortening velocity of a fiber and the output velocity of the muscle tendon unit (MTU). Fiber rotation can provide a velocity advantage by increasing the gear ratio (MTU velocity/Fiber velocity) with which a muscle operates. However, this velocity advantage comes at a cost to force since a smaller component of the fiber force is oriented along the line action. A recent study has shown that a muscle’s gear ratio varies depending on the load such that a muscle operates with a high gear during rapid contractions and low gear during forceful contractions. Here, we examine whether a similar automatic gearing mechanism can be replicated in artificial pneumatic “muscles”. We used Mckibben actuators, which shorten in tension when filled with compressed gas. Similar to real muscle fibers, the actuators expand radially during shortening to maintain a near constant volume, a feature known to be a critical part of the variable gearing mechanism in pinnate muscles. We used an array of McKibben actuators, oriented spatially to mimic a pinnate muscle, to quantify the system’s gear ratio when acting against a range of loads. Video was used to measure the gear ratio during each contraction. Similar to pinnate muscles, the gear ratio decreases significantly with increasing load. Variable gearing results from load-dependent variation in actuator rotation, as has been demonstrated for natural muscles. We show that variable gearing can be mimicked by an artificial pneumatic muscle system and suggest that actuator designs inspired by pinnate muscle architecture may provide a significant performance advantage. Supported by NIH AR054246 to EA.