Mechanical Characterization and Bioanalysis of Micro- Grooved Flow Diverters

Flow diverters (FDs) use fine-meshed tubes to divert blood flow away from the aneurysmal cavity to cure aneurysm and remodel the blood vessel network. However, current FDs are created from woven metal wire and can fail by migration, malposition, or restenosis. Recent studies show that the failure of FD can cause late thrombosis, embolism and rupture by inducing low grade constant inflammation, stent rubbing and delayed bio-acceptance of the FD. In this research, we studied the effect of micro-grooving of nitinol FDs on cell adhesion, proliferation and differentiation of fibroblast and endothelial cells. The effect of grooving on mechanical flexibility, longitudinal, radial and bending strength was also studied. Fined meshed flow diverters was fabricated using laser machining with custom made automated actuator system. FD surfaces were polished using Buhler grinding machine and sand paper. Surface finish and quality was assessed by scan electron microscope (SEM). Helical micro-grooving on the FD surface with three different depths (5 mm, 10 mm and 15 mm) was also done using laser machining system. Groove profile and surface roughness of the groove were quantified using 3D profiometer and SEM images. Longitudinal and bending strength, and radial expansion of FDs with and without grooving were evaluated using universal testing machine with high precision load cell and custom made jig fixture. FDs without groove were used as control group. All mechanical tests were designed based on the standard ASME testing procedures. For bioanalysis, FDs with and without micro-grooves were placed in a 3D printed biocompatible PLA tube and filled by collagen matrix with fibroblast and endothelial cells. After 1, 3 and 5 days of seeding, the cell proliferation, adhesion and differentiation were measured. The results show that surface grooves with 5 mm and 10 mm of depth did not alter mechanical properties of the FDs significantly. However, 20 mm of depth compromised the mechanical integrity of the FDs significantly. Both fibroblast and endothelial cell proliferation and differentiation was also improved in a grooved FD. Results also show that the cell adhesion to grooved FD was much higher than that of the non-grooved FDs for both types of cell. However with increase of the groove depth does not seem to have higher proliferation and adhesion. This study will contribute in understanding the impact of surface engineering of FDS and hence will help to design more efficient and functional fine meshed flow diverters (FDs) for the treatment of aneurysm.