Bent out of shape: Bioinspired vertebral column morphology and mechanics

Abstract

The vertebral column plays an essential role in body stiffness and swimming. Greater body stiffness results in greater mechanical outputs from the body on the environment. Previous work in bioinspired systems has shown that changing the length of the intervertebral joint changes the mechanics of the whole column. Our goals were to test the effects of centrum morphology and intervertebral joint length on mechanical outputs of the vertebral column using bioinspired models. We expected that centrum angle, joint length, and bending angle would all be significant effects in our statistical models. We designed five 3-D models inspired by vertebral morphology of fishes, humans, and marine mammals, and models were printed on a 3-D printer. We constructed 12 motion segments (centrum – joint – centrum) of varying joint length for each centrum morphology. A moment arm was added to one end of the motion segment to insure pure bending and eliminate shear. We tested mechanical properties of motion segments on a materials testing system measuring force (N). From the force outputs we calculated moment (Nm), Work (J), and Bending Stiffness (Nm2). Increasing the bending angle during testing, increased the moment and work produced by the system, while it decreased the bending stiffness. By increasing joint length we measured decreases in each of those mechanical properties. The marine marine mammal models, regardless of joint length, always had the largest mechanical outputs while the fish model with an intermediate centrum angle had the lowest. These data suggest that convex and flat models are consistently stiffer than concave models. Our data show the relation between centrum shape, joint length, and their associated mechanical outputs is perhaps not linear. Building additional models will allow us to further explore morphospace and better understand the conserved centrum shapes we see in among vertebrate groups. This research was funded by NSF grant DBI 1262239.