Towards an Artificial Bullfrog: Development of a Kinematically Realistic, Articulated Skeletal Model
Amy Cook, Perry Wood, Theodore A. Uyeno · 2020
Abstract Towards an Artificial Bullfrog: Development of a Kinematically Realistic, Articulated Skeletal ModelThe purpose of this project was to create a high resolution, physical model of a realisticallyarticulated bullfrog skeleton. Such a skeletal model would be beneficial to biomechanicists whostudy locomotion and behavior, to surgeons for planning complex surgeries, and to roboticistswho desire a life-like robotic platform. Here we describe a unique process that resulted in arapid-prototyped, articulated skeleton that incorporated scanned bone geometry and actual jointkinematics.The workflow began with collecting anatomical and behavioral data. We imaged the bullfrogskeleton in three-dimensions using a GE lightspeed VCT scanner (512x512x302 slices, 350x350x625 μm resolution). Next, we manually defined the major bone groups and jointsresponsible for the largest motions and deformations apparent in the bullfrog feeding lunge. Thisresulted in a tessellated computer model that was segmented to contain twenty-five links andtwenty-six joints. We then used image digitizing software (Didge, A. Cullum, Creighton Univ.)to analyze individual frames of high-speed and X-ray video recordings of frog feeding lunges toassess the kinematic joint parameters. For each joint we measured the degrees of freedom andranges of motion.The next step in the workflow involved using SolidWorks (Dassault Systems, Concord MA) tomodify the bone groups by adding articulated joints with realistic kinematics. Because biologicaljoints employ complex, flexible soft tissue connections, they were inappropriate for modelingusing a rapid prototyping system. As such, we replaced the biological joints with moreconventional engineering joints that we designed to mimic the observed degrees of freedom andranges of motion. Finally, to print the skeleton, we scaled it up by a factor of three to meet theminimum resolution of the rapid prototyping machine (Dimension 1200es Series fuseddeposition 3D printer).This workflow resulted in a geometrically accurate physical model with joint kinematics thatresembles a real bullfrog skeleton. Ultimately, we would like to use this skeletal model as afoundation for testing biological hypotheses of form and function. As such, there are a number ofareas of which we would like to progress with this project. More realism could be achieved bysegmenting and modeling some of the less dynamic bones and joints. Also, with the addition ofartificial muscle, this kinematic skeleton could be used as a basis for realistic robots that allow usto test hypotheses of neural control.