Quantifying Shear Stresses in Tissue Engineered Aortic Heart Valves

Present heart valve prosthesis have limitations such as capability to grow, repair and remodel post implantation. Tissue engineering offers to be a promising alternative to overcome these limitations. Maturation of seeded human cells on the valve subjected to favorable growth conditions in the bioreactor is critical to the success of tissue engineered heart valves. Mechanical stress and strain which results from the pressure and flow conditions in the bioreactor plays a critical role on the developing valve tissue and are currently unknown. The goal of this research is to relate the magnitude of wall shear stress (WSS) within the heart valve prosthesis in the bioreactor to the dynamically changing valve geometry and the flow during the systolic phase. Valve opening geometries during the systolic phase for three valve sizes (12.3, 18.45 & 24.6 mm diameter) were obtained first using fluid-structure interaction simulations. The geometries were then used in transient computational fluid dynamics simulations (CFD) with refined near-wall boundary mesh and prescribed flow rates as velocity boundary condition at the inlet. From the simulation results we identified regions of shear stresses with high magnitudes, which were primarily caused either due to accelerating fluid or separation of the boundary layer. We also developed a regression model to estimate shear stress (50th and 99th percentile) as a function of flow-rate and geometric orifice area (GOA). The data we report and the model developed in this study can be used to estimate WSS experienced by the tissue in the valve during various flow conditioning protocols, thereby assisting researchers to progressively tune bioreactor flow conditions to maintain healthy cells. This contribution can aid in the optimization of maturation protocols for tissue engineered heart valves