Design, Simulation and Fabrication of Novel Flat-Wire Braided Flow Diverter for Cerebral Aneurysm

Cerebral aneurysm is a weakened cerebral artery which causes localized ballooning of the blood vessel. As an aneurysm grows, it puts pressure on adjacent tissues and may eventually rupture, leading to severe events or even sudden death. Today the flow diverter, a stent-like mesh device, has gained increasing popularity for the endovascular treatment of cerebral aneurysms. The mechanism is to stop the blood flow into an aneurysm via the fine-mesh structure of the flow diverter to reduce the risk of rupture. It also serves as a scaffold for endothelialization, effectively sealing off an aneurysm from the body circulation. The paradigm shift in the treatment preference from traditional craniotomy reflects the growing confidence in the effectiveness of the flow diverter for managing cerebral aneurysms.<br/><br/>Braided flow diverter is currently used to treat cerebral aneurysms, with the braiding technology adopted to build stent-like mesh devices. Braiding is considered to be more cost-effective when compared to other stent fabrication techniques such as laser-cutting. When braiding, round wires extending from bobbins can be secured to the end of a mandrel under tension to form a braided device around it. In this paper, instead of using round wires, a novel flat-wire design with the wire dimension of 25 μm in thickness and 127 μm in width was investigated. This unique wire geometry possesses a higher aspect ratio that results in thinner struts and greater metal coverage (less opening). It is believed that thinner struts reduce the low wall shear stress zones and thus the risk of in-stent stenosis, a significant complication of narrowed arteries. Therefore, using flat wires could reduce the occurrence of in-stent stenosis, while increasing the metal coverage to cut down the blood supply to the aneurysm simultaneously.<br/><br/>A flat-wire braided flow diverter was investigated in this paper. Finite element analysis (FEA, ABAQUS) and computational fluid dynamics (CFD, ANSYS) were conducted to evaluate the mechanical integrity and hemodynamic behavior under various conditions consistent with the current practice. CFD models were analyzed based on an ideal aneurysm assembly with a flat-wire braided flow diverter implanted to evaluate its therapeutic effects. Prototypes were fabricated in-house using a braiding machine with the capacity of up to 64 bobbins, followed by the validation of bench tests for proof of concept. FEA simulation results showed no material damage occurred during the manufacturing and deployment processes as the strains were within the safety range. CFD simulation results showed the flat-wire braided flow diverter stopped a significant portion of the blood flow into an aneurysm. The velocity streamlines helped visualize the effectiveness of the increased metal coverage. These conclusions suggest that the flat-wire braided flow diverter has a great potential to achieve the best possible clinical outcomes.