Fluid-Structure Interaction Analysis of a Collapsible Axial Flow Blood Pump Impeller and Protective Cage for Fontan Patients.

Limited donor organs and alternative therapies have led to a growing interest in the use of blood pumps as a treatment strategy for patients with single functional ventricle. The present study examines the use of collapsible and flexible impeller, cage and diffuser designs of an axial blood pump for Fontan patients. Using one-way fluid-structure interaction (FSI) studies, the implications of blade deformation on blood damage and pump performance was investigated for flexible impellers made from biocompatible materials, including Nitinol, Bionate 80A polyurethane, and silicone, for flow rates between 2.0-4.0 L/min and rotational speeds of 3000-9000 RPM. The level of deformation experienced by a cage and diffuser made of surgical stainless steel (control), Nitinol, Bionate 80A polyurethane was also predicted using one-way FSI. The fluid pressure on the surface of the impeller, cage and diffuser was determined using computational fluid dynamics (CFD), and then the surface pressure was exported and used to determine impeller, cage and diffuser deformation using finite element analysis (FEA). Finally, deformed impeller geometries were imported into the CFD software to determine the implication of deformation on pressure generation, blood damage index, and fluid streamlines. It was found that rotational speed, and not flow rate, is the largest determinant of impeller deformation, occurring at the blade trailing edges. The models predicted the maximum impeller deformation for Nitinol to be 40nm, Bionate 80A polyurethane to be 106um, and silicone to be 2.8 mm, all occurring at 9000 RPM. The effects of silicone deformation on performance were significant, particularly at speeds above 5000 RPM where a decrease in pressure generation of more than 10% was observed. Despite the loss in pressure generation, the pressure generation at 5000 RPM exceeded the level required to alleviate Fontan complications. A blood damage estimation was performed and levels remained low across the models. The effect of significant impeller deformation on blood damage was inconsistent and requires additional investigation. Cage and diffuser geometries made of steel and Nitinol deformed minimally but Bionate 80A experienced unacceptable levels of deformation, particularly in the free-flow case without a spinning impeller. These results support the continued evaluation of a flexible, pitch-adjusting, axial-flow, mechanical assist device as a clinical therapeutic option for patients with dysfunctional Fontan physiology.