Topology, dynamics, and control of an octopus muscular hydrostat

Muscular hydrostats, such as octopus arms or elephant trunks, lack bones entirely, endowing them with exceptional dexterity and reconfigurability. Key to their unmatched ability to control nearly infinite degrees of freedom is the architecture into which muscle fibers are weaved. Their arrangements is, effectively, the instantiation of sophisticated mechanical programs that mediate, and likely facilitate, the control and realization of complex, dynamic morphological reconfigurations. Here, by combining medical imaging, biomechanical data, and direct numerical simulations, we synthesize a 3D computational analog of an octopus arm, and begin to unravel this complexity. We show how arm motions can be understood in terms of storage, transport, and conversion of topological quantities, effected by basic muscle activation templates. These, in turn, can be composed into higher-level control strategies that, compounded by the arm's mechanical compliance, are demonstrated in a range of object manipulation and retrieval tasks. Overall, this work significantly advances modeling and simulation abilities in the space of heterogeneous and active structures while exposing design and algorithmic principles pertinent to muscular hydrostats, with implications in biology, robotics, and control.