## 1 Introduction  
A cerebral aneurysm, also known as a brain aneurysm, is an abnormal blood-filled bulge or dome of a blood vessel, typically an artery, caused by weakening of the blood vessel due to cerebrovascular diseases/disorders. If untreated, a cerebral aneurysm presents a high risk of rupture, and may lead to haemorrhic stroke--a leading cause of disability and death around the world. The mechanisms behind the formation and developing of aneurysms have not been fully understood, but there is evidence that high shear stress and blood velocity may provide the hemodynamic environment for degenerative vascular injury [1]. The implantation of an intravascular device in the damaged vessel has been proposed as a way to prevent the developing of the aneurysm and its possible rupture. Among various devices, the flow-diverting stent (FDS), a self-expandable, strut-braided, mesh device, is presently widely used for treating aneurysms, where intra-aneurysmal flow reduction induces progressive aneurysm thrombosis in most patients. The degree of flow modification necessary to induce a complete aneurysm occlusion among patients is not yet clear due to the complexity involved in the changed hemodynamics upon the use of stents. However, the changed hemodynamics are very important for planning the correct treatment [2; 3; 4]. Studies have been recently published regarding this topic and it is generally accepted that the success of FDS treatment with a satisfactory aneurysm occlusion depends on the changed hemodynamics [5; 6]. Furthermore, it is recognized the porosity of stents plays an important role in the changed hemodynamics; lower porosity can reduce the blood flow into the aneurysm, thus increasing the likelihood of aneurysm occlusion. On the other hand, lower porosity can increase stent stiffness, thus introducing difficulties in stent deployment as well as the possibility of harming arterial walls from the excessive radial force [7]. Typically, the FDA-approved endovascular stents for cerebral applications have porosities between 80% and 90% [7]. The stent design influences stent performance in reducing the aneurysmal inflow [7; 8]. During last decades various evaluations of the hemodynamic changes in an aneurysm due to the presence of FDSs have mostly been conducted in vitro and/or by means of numerical studies. [PERSON] and coworkers extensively studied the aneurysmal flow circulation in the presence of a FDS, illustrating that the capability of diminishing the inflow is a function of the stent shape and strut diameter [9; 10]. Studies on the stent effects on aneurysm circulation have also been carried out by using computational fluid dynamics (CFD) [1; 7; 8; 11; 12; 13; 14]. For example, the effects of stent mesh shape were investigated by [PERSON] et al. [11], [PERSON] et al. [15] [PERSON] and [PERSON] [16], [PERSON] and [PERSON] [17] and [PERSON] and [PERSON] [18]. More recently, [PERSON] et al. [19; 20; 21] analysed the change of flow pulsatility in the aneurysm post the FDS treatment. Some other studies have investigated and evaluated the flow reduction within aneurysmal sacs, depending on aneurysm morphology [22; 23; 24] and inflow rate boundary conditions [25]. Recent studies have investigated the connection between hemodynamics and treatment outcomes [5; 26; 27; 28; 29]. Although experimental and numerical studies and additional clinical trials have already led to significant advances in this field, the effects on local hemodynamics have not been fully understood [21; 26; 30]. Besides complete aneurysm occlusions in the majority of the FDS-treatment cases, post surgical and long term aneurysm ruptures have also been reported [31]. In this study we propose a new design of biodegradable coarse-mesh stent and we evaluated its performance, as compared to two finer-mesh commercial stents. The aim of the study is to evaluate its capability of reducing the aneurysmal flow and promoting the desired occlusion.