CAREER: Biomechanics of Amphibious Fish Fins and Mechanical Principles of Stiff Lightweight Structures

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This Faculty Early Career Development (CAREER) grant will use engineering to discover the biomechanical specializations that allow amphibious fish to move on land. This is of scientific interest because these fish use their thin and lightweight fins to apply very large forces to move on land. Through biological experiments, engineering device design, and mathematical modeling, the project seeks to uncover relationships between the form and function of fins used to move on land. The knowledge gained in this project will impact several fields. Understanding the mechanics of walking fish will help address the substantial challenges in designing agile robots capable of traversing diverse environments. This is important for future use of such robots for search and rescue operations and remote ecological studies to go where it is impossible or unsafe for humans to go. Learning about amphibious fish is also critical for understanding how terrestrial vertebrates evolved from an aquatic ancestor that used its fins to move on land around 400 million years ago. The project’s synergistic education and outreach activities include curriculum development, a multi-year scaffolded mentorship plan for high school students, and student-developed hands-on museum exhibits on amphibious fish that will also serve as novel teaching aids for school teachers. These will be designed to broaden participation in STEM from K-12 through college and incubate the next generation of interdisciplinary scientists.This interdisciplinary research objective is to discover how the mudskipper, an amphibious fish, has specialized its fin design and biomechanics to withstand forces for moving on land and test the hypothesis that they resist ground forces using the nonlinear effect of curvature-induced stiffness. The curvature-induced stiffness principle helps human feet withstand ground forces, and aquatic fish fins also manifest elements needed for that effect. But the anatomical manifestations are quite different in fins and feet, raising the question of how amphibious fish stiffen their fins on land. The project will combine experiments with theory to investigate the multi-scale, hierarchical, and composite structure of the fins of amphibious (mudskippers and bichirs) and aquatic fish (gobies and mackerels) from the whole organism (~10–100 millimeters) down to the fin’s internal structure (~10–100 micrometers). The specific aims, with fundamental impact on locomotion biomechanics and fish fin structural mechanics, are to (i) measure in vivo forces on mudskipper fins using a novel optical force sensor, (ii) identify critical stiffness-contributing anatomical elements using in vitro mechanical tests on amphibious and aquatic fish fins, and (iii) discover the specializations of amphibious fish fins and derive generalizable biomechanical principles of a fin morpho-functional space by combining 3D micro-computed tomography (microCT), in vivo force, and in vitro stiffness data with multi-scale, composite-elastic fin models. Discoveries on the fin’s form-function relationships could be crucial for biologists studying the development and evolution of fins and limbs. Also, novel appendage designs may considerably enhance the effectiveness of multi-terrain robots.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.