Generative design as a tool to analyze the uncertain loading regimes of intricate skeletal structures

The morphology of a skeletal structure is driven in part by the forces it endures over evolutionary time. We demonstrate that generative design, an iterative engineering tool, can yield insight into the loading regimes of complex skeletal elements. With only a simple model of the spatial constraints and potential forces seen by a skeletal element, we generated analogous structures. We used this technique to provide insights into the specialization of the radial elements of batoid pectoral fins, a case that would be challenging to analyze by conventional means. Particular configurations of generative designs resulted in structures with a morphology remarkably similar to that of real radials. We suggest that these cases reveal the loading configurations that the real radials have evolved to withstand., We imaged material from two batoid fish species from the collection of the Biomechanics Lab at Friday Harbor Labs. The longtailed river stingray, Plesiotrygon iwamae, is an undulatory swimmer with a rounded pectoral fin profile producing multiple wave periods along the wing per flap. The banded eagle ray, Aetomylaeus nichofii, is an oscillatory swimmer with a triangular fin profile generating a half wave period per flap. We dissected the skeleton of the pectoral fin from both species and micro-CT imaged the samples on a Bruker Skyscan 1173. We produced volume and surface renderings of radials with the free, open source software 3D Slicer.
Fusion 360 (Autodesk, San Francisco), was used under educational license for computer aided design (CAD) and solving the generative design cases. The simulation requires geometric dimensions, loadings, and material properties. We elected to use a model with biologically based aspect ratio and arbitrary size, loading, and properties. We specified geomet..., , # Generative design as a tool to analyze the uncertain loading regimes of intricate skeletal structures

[https://doi.org/10.5061/dryad.280gb5n14](https://doi.org/10.5061/dryad.280gb5n14)

We have submitted our raw microCT image stacks (**CT_data.zip**), 3D meshes of structures produced using our generative design method (**Generative_Design_Models.zip**), 3D meshes of indvidual batoid radials (**Radial_Models.zip**), Shape data taken from both sets of meshes and used to calculate volume fractions (**Volume_Fraction.csv**).

## Descriptions

### **CT\_data.zip**

* Folder *RayWing01_14.9um_2k_Rec2* : BMP image stack of 14.9 micron resolution scan of a section of pectoral fin from a preserved speciment of *Plesiotrygon iwamae* produced on Brucker Skyscan 1173.
* Folder *RayWing02_13.8um_2k_Rec* : BMP image stack of 13.8 micron resolution scan of a section of pectoral fin from a preserved speciment of *Aetomylaeus nichofii* produced on Brucker Skyscan 1173.

### **Generative\_Design\_Mode...,