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Biomechanics

Biomechanics - Poster Session D

Poster E7 - Optimizing Ovine Cardiac Material Models For Use in Finite Element Modeling

Friday, October 25, 2024
3:30 PM - 4:30 PM EST
Location: Exhibit Hall E, F & G

Introduction:  Blunt force trauma to the chest can cause damage to the heart through energy transfer [1]. To help further study these injuries, computational models of ovine surrogates are being developed because of their anatomical similarities to humans [1]. This study aims to optimize a material model for use in explicit finite element modeling software (the study employs LS-Dyna) to accurately represent published experimental data of cardiac tissue in biaxial tension [2].  The model seeks to accurately represent heart tissue mechanical behavior, enabling more biofidelic cardiac behavior for use in silico for injury criteria development.

Materials and

Methods:  We employ an implementation of the well-known Fung hyperelastic material model [3] known as *MAT_HEART_TISSUE in LS-Dyna (ANSYS, Location, USA) in an optimization scheme. This material model was selected because it can account for anisotropy. One material model variable (out of 4) was changed at a time throughout the optimization process to ensure unique combinations. Bounds were selected based on data from Javani et al. [2] and mean experimental data fits were used as the starting point. Various matrices were run to help match simulated data to experimental data.  First, +/- 1 and 2 standard deviations of the baseline parameters were run, then magnitudes were adjusted for each variable. Lastly, the ratios between C11:C12 and C22:C12 were investigated due to their effect on the behavior based on fiber directionality. To determine the model's accuracy, the evaluation metrics are the sum of squared errors in the fiber and cross fiber direction, mean SSE, and the squared integral of the simulated data minus the squared integral of the experimental data over the squared integral of the experimental data. For both evaluation metrics the closer to value is to zero is better.

Results, Conclusions, and Discussions: Results and

Discussion: The sensitivity analysis results revealed that the C variable has the most significant impact on the model. This variable is known to be the main driver of magnitude in both the fiber and cross fiber direction. This insight allowed for improvements in the optimization, achieving a value very close to zero, 0.11 for the evaluation metric for the left ventricle. The mean SSE for the left ventricle was 21.41, while for the right ventricle, we obtained an evaluation metric of 0.17 and a mean SSE of 3.87.

Conclusion: Our findings demonstrate a strong correlation between the simulated model and the experimental data [2]. The sensitivity analysis highlighted the significance of variable C, and optimization efforts led to a close match between the simulated and experimental data, particularly for the right ventricle. These results underscore the developed model's potential in accurately representing cardiac tissue behavior under elevated tensile loading. Future work will focus on refining the model and exploring its applicability to other heart regions.

Acknowledgements (Optional):  Acknowledgements: Work was funded by US Army Research Lab, Grant W911NF2120034. This project was supported in part by the Wake Forest Summer Research Internship Program in the Department of Biomedical Engineering at Wake Forest University School of Medicine.

References:
[1] Gibbons M. J. Biomech. Eng. (2015) 137:1-9.
[2] Javani, S., Gordon, M., & Azadani, A. N. (2016). Biomechanical Properties and Microstructure of Heart Chambers: A Paired Comparison Study in an Ovine Model. Annals of biomedical engineering, 44(11), 3266–3283. https://doi.org/10.1007/s10439-016-1658-7
[3] Fung, Y. C., Fronek, K., & Patitucci, P. (1979). Pseudoelasticity of arteries and the choice of its mathematical expression. The American journal of physiology, 237(5), H620–H631. https://doi.org/10.1152/ajpheart.1979.237.5.H620