Poster AA8 - Design of a single body topology optimized chest wall for biophidelic flexural response in blast

Introduction: Human surrogate models are valuable tools for advancing the development and evaluation of personal protective equipment (PPE) to protect warfighters from traumatic injuries. The ideal surrogate is biofidelic, low cost, and provides data easily interpreted as injury risk. These characteristics are particularly true of the rib cage which provides structure to the surrogate thorax and protects internal organs of critical interest including the lungs. To ensure calculated injury risk predictions for these organs are accurate, the compliance of the surrogate ribs must be as biofidelic as possible. The purpose of this work is to compare the biofidelity and morphometric properties of three structurally optimized surrogate rib cages designed under different loading conditions and intended for fabrication via custom molding.

Materials and

Methods: High fidelity models of the rib cage, sternum, costal cartilage, lungs and thoracic spine were obtained along with their corresponding material properties from the Global Human Body Models Consortium (GHBMC) computational human body model. A design space was created through blending of the anatomical models. Three loading conditions were applied to structurally optimize the design space by minimizing volume fraction while targeting compliance values obtained from cadaveric data [1]. These loading conditions included 1) a single uniform load across the sternum, 2) three vertical loading “bands” applied at the sternum, costal cartilage joint, and lateral ribs to represent 0, 45, and 90 degree loading scenarios, and 3) individual loading points on the sternum and ribs at 0, 45, and 90 degrees mimicking those tested in Kindig’s cadaveric work. Each design was optimized under the assumption of fabrication via molding using a 30 MPa epoxy.

Results, Conclusions, and Discussions: Final designs were subjected to 20 mm of deformation via static loading conditions at the sternum in LS Dyna to calculate force required. This resultant force for each design was compared to the target of 100 N, taken from the force deformation curves in Kindig et al [1]. The same process was repeated for 10mm of deformation at the 45 degree angles and 5 mm of deformation at the 90 degree angles with corresponding target forces of 50 and 25 N. Method 3 was found to be too computationally expensive to converge to the target in a reasonable length of time (2000 iterations). Methods 1 and 2 generated models that showed promise in replicating the cadaveric results.

Future work will evaluate the computational response to dynamic loading, as well as physical testing of the optimal design in a surrogate subjected to blast trauma. By optimizing the design to achieve compliance on par with human bone, the data collected on internal organs protected by the ribcage will yield more accurate injury risk predictions.

References:
1. Kindig, M. W., Lau, A. G., Forman, J. L., & Kent, R. W. (2010). Structural response of cadaveric ribcages under a localized loading: stiffness and kinematic trends (No. 2010-22-0015). SAE Technical Paper.

Acknowledgements (Optional): This research is supported by U.S. Army Medical Research Acquisition Activity under contract # HT942523C0053. The views, opinions and/or findings contained in this poster are those of the author(s) and should not be construed as an official Department of the Army position, policy or decision unless so designated by other documentation.