Grow a Backbone: Bending Mechanics of Biomimetic Intervertebral Joints

Abstract

There is huge variation in vertebral centra morphology both within and among classes. While research has noted and described these differences in detail, it has not adequately explored how centrum shape affects joint stiffness. My research explored how the existing variation between fish and mammal vertebral centra affects the loading and deflection of the intervertebral joint under homologous conditions of size and materials. I expected that bending forces would be proportionally related to the volume of intervertebral material as affected by intervertebral distance and centra morphology. To test the stiffness of the joint, I made multiple motion segments of ABS plastic using silicone as the intervertebral material. Each centrum had a different angle of concavity, flat face, or convexity mimicking fish, land mammals and marine mammals, respectively. The Material Testing System deflected the motion segment measuring the force required at the end of a moment arm. Land and aquatic mammals create statistically similar bending moments that are distinct from all of the fish inspired designs, which are all statistically similar to each other. The trends within these findings raise more questions about how concavity and intervertebral length affect stiffness, stress, moment, and overall bending performance with biomechanic and evolutionary implications.