In Vitro Biomechanical Examination of Excised Calcified Aortic Leaflet Tissue for Material Property Assessment and Improved In Silico Modeling

Transcatheter aortic valve replacement (TAVR) patients suffer from calcific aortic valve disease (CAVD), leading to aortic stenosis (AS). Computational modeling has become a vital tool for patient-specific analysis in cardiovascular interventions, particularly for TAVR. The success of in silico TAVR modeling relies on accurately defining leaflet calcium deposit material properties, as this greatly influences device deployment. However, the material characteristics of leaflet calcification remain contested. Valvular calcium deposits are significantly stiffer than native tissue, yet their material properties remain poorly defined. This study addresses this gap by utilizing micro-CT scanning, benchtop testing, and inverse finite element analysis (FEA) to refine material definitions and enhance TAVR simulation results. Calcified aortic valve specimens were collected and analyzed using high-resolution micro-CT scanning and MATLAB processing to segment calcified regions based on radiographic density. Accordingly, each leaflet was divided into 11 HU ranges, 1 for soft tissue, and 10 equally spaced HU ranges for the calcified regions. Uniaxial compression testing was performed, and inverse FEA simulations replicated benchtop testing with voxel-based leaflet meshes using a crushable foam plasticity model. An optimization scheme adjusted calcium deposit material properties to achieve a 95% match between the in silico and in vitro force responses. Data analysis was conducted to determine optimal material properties, incorporating an examination of the impact of patient demographics (i.e., sex). Results were also applied to TAVR simulations, demonstrating differences in simulation outcomes with varying properties. The calcium layers from the in vitro CT data and in silico models aligned extremely well. Successful inverse FEA resulted in force–response curves matching within 95% for all tested leaflets. Stress concentrations were examined, where maximum von Mises stress values were in the range of 25 MPa. Average female patients’ calcium layer stiffness was approximately 30% higher (p < 0.1) than that of the male patients. Incorporating the improved, validated calcium properties into updated TAVR simulations revealed that the updated calcium deposits exhibited greater stiffness than previously modeled. This led to variations in stent deployment and leaflet stresses/strains, as well as increased contact pressure in the lumen. This study is among the few in the field to examine physical aortic valve specimens for determining optimal material properties of valvular calcium deposits. Furthermore, to our knowledge, it is the first to demonstrate that calcium deposits can be modeled using a crushable foam plasticity formulation, enabling a more accurate representation of their structure and behavior while being validated with in vitro data. This workflow has also revealed potential differences in calcium stiffness between male and female patients, with significant implications for the modeling of interventional cardiac procedures and patient-specific analyses in the future.