Structural Design Optimization of Braided Nitinol PDA Occluders: A Parametric DOE Approach to Radial Compliance

Abstract

The PDA occluder is a transcatheter minimally invasive device designed to close the anomaly channel between the aorta and pulmonary artery. It is important to obtain optimal ratio of radial stability and compliance due to the great anatomical variability of ductal morphology. As the mechanical behavior of the Nitinol braided structure determines the effectiveness and safety of such devices, this study investigates the effect of braid angle, wire diameter, and braid pattern on the deformation of PDA occluder waist under physiologically relevant radial pressures. Parametric models with braided structure were developed and analyzed via finite element simulation taking into account geometric non-linearity (large deflection) in combination with linear elastic material model of Nitinol, for braid angles of 30° and 60° (with an additional 45° midpoint check), and wire diameters of 80 and 120 µm (with an additional 100 µm midpoint check), across plain and 2×2 braid configuration. Wires were modeled as one-dimensional beam elements; the analysis was performed with the consideration of frictionless and frictional contacts at the wire intersections, however, no significant differences in deformation was found. Radial pressures 5 kPa and 30 kPa corresponded to low- and high-pressure physiological condition of the duct, respectively. Full factorial design of experiments (DOE) was performed in order to evaluate the contribution of design parameters to deformation behavior, using 30°/60° braid angles and 80 µm/120 µm wire diameters as factorial levels, while the intermediate 45° braid angle and 100 µm wire diameter were used for cross-verification of results. Thinner wires and the 2×2 braid configuration resulted in greater radial deformation and thus greater compliance of the structure, while thicker wires reduced deformation. The influence of braid angle depended on the braid configuration. Wire diameter was found to be the most influential factor, followed by braid pattern and braid angle, with a noticeable interaction between wire diameter and braid pattern. Overall, the findings presented here allow the development of a geometry-driven framework to design effective PDA occluders.