Robots for Biomechanical Testing: How Intervertebral Joint Length and Number Impact Swimming Performance

Jonathan Hirokawa, Vassar College’10, Sonia Roberts, Vassar College ’10, Nicole Krenitsky, Vassar College ’11, Carina Frias, Vassar College ’11 with Prof. John Long and Faculty Research Assoc. Marianne Porter

To test hypotheses about how skeletal morphology and swimming mechanics modulate performance, we combined biological and robotic approaches. Our morphological variant of interest was the vertebral column, while our mechanical variables consisted of swimming mode and tailbeat frequency. To investigate these variables, we created a new biomechanical research tool: a swimming Mobile Autonomous Robot for Mechanical Testing (MARMT) with programmable behaviors. MARMT allowed us to test the mechanical behavior of biomimetic vertebral columns, made from collagen based gelatin cross-linked with glutaraldehyde, under realistic hydrodynamic loading conditions. The combination of biological materials that mimic the chemical structures found in fishes and the robotic platform served as a biologically relevant model. We varied the number of intervertebral joints on these columns between zero and twelve. Three replicates of each condition were sampled during both straight swimming and fast-start escape responses at five different tail beat frequencies while holding tail beat amplitude constant. We examined how these parameters impacted MARMT’s performance characteristics such as velocity, acceleration, rotation, and curvature and amplitude of the tail. Preliminary analysis supports our hypotheses that increased frequency and intervertebral joint number lead to higher maximum and mean accelerations. Extrapolating our results to biological systems, more and smaller intervertebral joints may provide an adaptive advantage for bursts of speed. This may allow for quicker escapes from predators or faster attacks on prey.