Benchtop proof of concept and comparison of iron- and magnesium-based bioresorbable flow diverters

Abstract

Objective: Bioresorbable flow diverters (BRFDs) could significantly improve the performance of next-generation flow diverter technology. In the current work, magnesium and iron alloy BRFDs were prototyped and compared in terms of porosity/pore density, radial strength, flow diversion functionality, and resorption kinetics to offer insights into selecting the best available bioresorbable metal candidate for the BRFD application.

Methods: BRFDs were constructed with braided wires made from alloys of magnesium (MgBRFD) or iron (FeBRFD). Pore density and crush resistance force were measured using established methods. BRFDs were deployed in silicone aneurysm models attached to flow loops to investigate flow diversion functionality and resorption kinetics in a simulated physiological environment.

Results: The FeBRFD exhibited higher pore density (9.9 vs 4.3 pores/mm2) and crush resistance force (0.69 ± 0.05 vs 0.53 ± 0.05 N/cm, p = 0.0765, n = 3 per group) than the MgBRFD, although both crush resistances were within the range previously reported for FDA-approved flow diverters. The FeBRFD demonstrated greater flow diversion functionality than the MgBRFD, with significantly higher values of established flow diversion metrics (mean transit time 159.6 ± 11.9 vs 110.9 ± 1.6, p = 0.015; inverse washout slope 192.5 ± 9.0 vs 116.5 ± 1.5, p = 0.001; n = 3 per group; both metrics expressed as a percentage of the control condition). Last, the FeBRFD was able to maintain its braided structure for > 12 weeks, whereas the MgBRFD was almost completely resorbed after 5 weeks.

Conclusions: The results of this study demonstrated the ability to manufacture BRFDs with magnesium and iron alloys. The data suggest that the iron alloy is the superior material candidate for the BRFD application due to its higher mechanical strength and lower resorption rate relative to the magnesium alloy.

Keywords: absorbable; bioabsorbable; biodegradable; bioresorbable; endovascular neurosurgery; flow diverter; stent.

Figure 1:

Left) Macroscopic images of a MgBRFD and FeBRFD. Scale bars are 2 mm. Right) Representative 4X normal magnification images of a MgBRFD and FeBRFD used for porosity and pore density calculations. Scale bars are 1 mm.

Figure 2:

Left) Radial force exerted by the MgBRFD and FeBRFDs versus device diameter during crushing and reexpansion between parallel plates. Solid lines and lighter shading represent the mean ± the standard error. Right) Crush resistance force for the MgBRFD and FeBRFDs.

Figure 3:

Left) Normalized time density curves for the MgBRFD and FeBRFDs. Solid lines and lighter shading represent the mean ± the standard error. Right) Mean transit time (MTT), inverse wash-in slope (WIS⁻¹), and inverse wash-out slope (WOS⁻¹) for the MgBRFD and FeBRFDs presented as a percentage of the control condition. *p < 0.05, **p < 0.005

Figure 4:

Left) Representative MicroCT 3D renderings of the MgBRFD and FeBRFDs over time. For both devices, the red represents tantalum and white represents the bioresorbable wires. Right) Reduction in % volume of bioresorbable wires in the MgBRFD and FeBRFDs over time. The dashed line represents the linear line of best fit for the FeBRFD (R² = 0.934, p = 0.034)