Project Description

Introduction

When a cerebral aneurysm ruptures and bleeds into the brain or surrounding area, hemorrhagic stroke occurs. This life-threatening event has a 50% mortality rate, resulting in half a million deaths worldwide each year. Unfortunately, 66% of the patients who survive a ruptured cerebral aneurysm still suffer permanent neurological deficits. There is a lack of physical models (laboratory phantoms) that can realistically mimic the biomechanical behavior of aneurysms during rupture. To better understand the aneurysm rupture mechanics, this study focuses on the design and implementation of a cost-effective and easy-to-fabricate phantom using a 3D printing technique. To facilitate a predictable rupture event in the phantom, we utilized a computational model to find the weak spots and adjusted the wall thickness, mimicking wall thinning phenomena. This phantom model can also be used to validate computational models, test stent and coil devices, and provide surgical training.

Methods

Aneurysm models from the Aneurisk dataset repository were employed—specifically, Cases 36, 39, and 42. MeshMixer was used to simplify the geometry file. A 3.175 mm diameter cylinder was created to simplify the inlet and outlet for easy fabrication and position. The geometry was then hollowed, and the vessel wall was thickened to 0.55 mm. These models were then meshed in Ansys Mechanical to be prepped for Computational Fluid Dynamics (CFD) analysis. CFD analysis was then performed on the models to find several essential properties contributing to aneurysm rupture, such as mean velocity, wall shear stress (WSS), and average pressure. The analysis aimed to identify areas of flow diversion to manually weaken the vessel’s walls at overlapping points of higher pressure and wall shear stress. The program chosen for analysis was Ansys Fluent; the vessel’s walls were treated as no-slip rigid walls. The blood flow within the models was treated as a transient pulsatile flow of a non-Newtonian fluid with a density (𝝆) of 1060 kg/cm3 and a Carreau viscosity model (𝜇) of 0.0035 Pa·s. At the identified points, the models were weakened by creating 4 mm spherical imprints in the inner vessel wall at distances of 0.4 mm, 0.45 mm, and 0.5 mm. The resulting thickness at these weak spots is 0.15 mm, 0.1 mm, and 0.05 mm.