Computational Design Optimization of Internal Ramp Geometry in Side-Port Embryo Transfer Catheters to Minimize Fluid Recirculation and Shear Stress

Abstract

The success of in vitro fertilization (IVF) relies heavily on non-traumatic embryo delivery. While end-opening catheters provide direct flow, they pose a risk of endometrial injury and embryo displacement due to high-velocity jetting, whereas conventional side-port designs minimize trauma but inherently suffer from fluid stagnation and elevated shear stress. This study aims to resolve this critical hydrodynamic trade-off by proposing a novel 'Flow-Guiding Internal Ramp Architecture' (FGIRA) integrated with an oval lateral aperture to eliminate dead zones while maintaining safe, low-velocity expulsion. Three-dimensional computational fluid dynamics (CFD) simulations were conducted using SolidWorks Flow Simulation based on the finite volume method to solve the Navier–Stokes equations. The study modeled the fluid as a Newtonian standard culture medium at 310.15 K, utilizing a mesh refinement strategy optimized for grid independence to comparatively analyze the hydrodynamic performance of four catheter configurations, focusing on velocity distribution, vorticity, and Wall Shear Stress (WSS). The results demonstrated that the Oval-FGIRA design successfully eliminated fluid recirculation and achieved a maximum WSS of 1.21 Pa within the 0.04 m/s injection speed regime. This value falls well within the physiological safety threshold (< 2 Pa), supported by a stable laminar flow regime (Maximum Local Reynolds Number = 49.95). In conclusion, unlike traditional side-port designs that merely redirect flow at the cost of high shear stress, the Oval-FGIRA establishes a breakthrough. By simultaneously eliminating fluid stagnation and dampening mechanical forces, the synergy between the internal ramp and oval aperture creates a superior hydrodynamic environment that minimizes mechanotransduction-induced cellular damage, offering a paradigm shift in catheter geometry to improve clinical pregnancy rates. However, at the injection velocity of 0.08 m/s, maximum wall shear stress exceeded the safety threshold at 2.10 Pa. Consequently, clinical implementation of the Oval-FGIRA is recommended for slow-to-immediate injection protocols.