In this proposal the PI will study how a desert dwelling lizard, the Sandfish, swims beneath the surface of a granular material. Imaging methods will be developed to surmount the difficulties of visualizing biological systems in opaque terrestrial media and computational modeling tools will be created to study the interaction of the organism with materials whose equations of motion are unknown. These efforts will occur in three interacting thrust areas: (1) Measurements of organism motion and dynamics: A multiplane, high speed and resolution x-ray imaging system will be built to obtain the first three dimensional kinematics of an organism moving within a complex medium. Both the kinematics and forces will be characterized as the substrate properties are systematically varied by use of an air fluidized bed. (2) Physics experiment to characterize response of granular media to swimming motions: Developing models of the locomotion will require understanding the physics of the material response in this regime in which the bulk of the material behaves like a solid except for a small region surrounding the organism which behaves like a fluid. The forces associated with maneuvering objects through the granular medium will be measured and the results use to produce an empirical model of force production. (3) Computer models of organism and granular media: As granular media are amenable to direct numerical simulation, development of a 3D Molecular Dynamics simulation interacting with the actuated objects (lizard models) used in experiment will result in numerical environment interaction models that can be used to interrogate the motion at the grain level as well as to create the first models of biological organisms moving within this material. The experimental data obtained from studying the organism will suggest actuation strategies that will be played through the physics experiments and validated models. This study will initiate the beginnings of a deeper understanding of movement within non-Newtonian media and thus will result in a new model system for locomotion biology, as well as models for locomotion. This work will create rapid modeling tools to aid design of robotic exploration and search & rescue devices that must burrow through challenging terrain. It will also gather students from a diverse range of backgrounds: physics students will interact with biology students to make progress on experiments and models. This program will serve as a springboard to develop a course examining control of locomotion, mechanical properties of biological actuators (muscle), skin friction, rheology of complex matter, etc. Outside the university, the program will provide outreach by engaging the public in visible and graspable science.
PI: Daniel I. Goldman, School of Physics, Georgia Institute of Technology, Atlanta, GA BACKGROUND: To feed, mate, and avoid predation, organisms must maneuver effectively in their environments; thus locomotion (running, swimming, flying, and burrowing) is a fundamental way in which living organisms confront the physical world. Nearly all experiments and models of terrestrial locomotion have been developed for running and walking on rigid, flat, no-slip substrates in which the possible complication of substrate flow has been ignored. In contrast, complexity in interaction with environment in aquatic and aerial locomotion via flying and swimming is recognized and well-studied. Physics has and will continue to contribute to aerial and aquatic biological locomotion problems since the rules of interaction with fluids are worked out: they require solving the well-established equations of hydrodynamics in the presence of moving boundary conditions which is always possible in principle. A great remaining frontier in biology is to understand locomotion of organisms within terrestrial substrates for which equations of motion like NS do not exist and for which visualization techniques are nearly non-existent. Terrestrial locomotion problems probe our fundamental ignorance of the basic laws of mechanics of particulate media. The proposed research seeks to understand the biology and physics of the movement of a small desert dwelling lizard, the sandfish (Scincus scincus). During NSF funding, we have imaged for the first time the movement of the sandfish as it "swims" within sand. The lizard sends a wave of body undulation down its back and propels itself forward in sand at about half the speed of the traveling wave. We have developed theoretical, computational and robotic tools to understand how the propulsion is generated and have shown that the animal uses the optimal wave amplitude to achieve its performance. The work will advance the fields of biomechanics and the physics of penetration and drag in granular media. The work will also advance modeling of robotic interaction with complex materials like those found in disaster sites.
