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

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.

Bioresorbable flow diverters for the treatment of intracranial aneurysms: review of current literature and future directions.

The use of flow diverters is a rapidly growing endovascular approach for the treatment of intracranial aneurysms. All FDA-approved flow diverters are composed of nitinol or cobalt-chromium, which will remain in the patient for the duration of their life. Bioresorbable flow diverters have been proposed by several independent investigators as the next generation of flow diverting devices. These devices aim to serve their transient function of occluding and healing the aneurysm prior to being safely resorbed by the body, eliminating complications associated with the permanent presence of conventional flow diverters. Theoretical advantages of bioresorbable flow diverters include (1) reduction in device-induced thrombosis; (2) reduction in chronic inflammation and device-induced stenosis; (3) reduction in side branch occlusion; (4) restoration of physiological vasomotor function; (5) reduction in imaging artifacts; and (6) use in pediatric applications. Advances made in the similar bioresorbable coronary stenting field highlight some of these advantages and demonstrate the feasibility and safety of bioresorbable endovascular devices in the clinic. The current work aims to review the progress of bioresorbable flow diverters, identify opportunities for further investigation, and ultimately stimulate the advancement of this technology.

Finite Element Analysis of the Septal Cartilage L-Strut.

Importance: Septoplasty is one of the most commonly performed operations in the head and neck. However, the reasons for septoplasty failure and the additional stress of performing a chondrotomy on the septal cartilage are not well understood. Design, Setting, and Participants: A finite element model of the nasal septum was created using a microcomputed tomography scan of the nasoseptal complex that was reconstructed into a three-dimensional model in silico. Testing included four common chondrotomy designs: traditional L-strut, double-cornered chondrotomy (DCC), curved L-strut, and the C-curve. Tip displacement was applied in a vector parallel to the caudal strut to simulate nasal tip palpation. Main Outcomes and Measures: With finite element analysis, the maximum principal stress (MPS), von Mises stress (VMS), harvested cartilage volume, and surface area were recorded. Results: The highest MPS for the L-strut, DCC, curved L-strut, and C-curve was identified at the corner of the chondrotomy. The MPS at the corner of the chondrotomy was reduced 44% when comparing the C-curve with the traditional L-strut. The VMS patterns showed compressive stress along the caudal septum in all models, but at the corner, the stresses were highest in the chondrotomies designed with sharp-angled corners. The VMS showed a 76% decrease when comparing the C-curve with the traditional L-strut. The stress across the anterior septal angle is also higher in models with sharp-angled corners. Cartilage harvest volumetric and surface area assessments did not show meaningful differences between shapes. Conclusions and Relevance: The highest area of stress is near the transition of the dorsal to caudal septum in all models. Stresses are relatively higher in chondrotomy shapes that contain sharp-angled corners. The relative reduction in MPS and VMS utilizing a C-curve instead of an L-strut may decrease the likelihood that the septum will deform or fail in this region. The volume and surface area of the C-curve are similar to that of the L-strut technique. Avoiding sharp-angled corners reduces the stresses at the corner of the chondrotomy and across the anterior septal angle. Using a C-curve may be an improved septoplasty design.

Multiple Aneurysms AnaTomy CHallenge 2018 (MATCH)-phase II: rupture risk assessment.

PURPOSE: Assessing the rupture probability of intracranial aneurysms (IAs) remains challenging. Therefore, hemodynamic simulations are increasingly applied toward supporting physicians during treatment planning. However, due to several assumptions, the clinical acceptance of these methods remains limited. METHODS: To provide an overview of state-of-the-art blood flow simulation capabilities, the Multiple Aneurysms AnaTomy CHallenge 2018 (MATCH) was conducted. Seventeen research groups from all over the world performed segmentations and hemodynamic simulations to identify the ruptured aneurysm in a patient harboring five IAs. Although simulation setups revealed good similarity, clear differences exist with respect to the analysis of aneurysm shape and blood flow results. Most groups (12/71%) included morphological and hemodynamic parameters in their analysis, with aspect ratio and wall shear stress as the most popular candidates, respectively. RESULTS: The majority of groups (7/41%) selected the largest aneurysm as being the ruptured one. Four (24%) of the participating groups were able to correctly select the ruptured aneurysm, while three groups (18%) ranked the ruptured aneurysm as the second most probable. Successful selections were based on the integration of clinically relevant information such as the aneurysm site, as well as advanced rupture probability models considering multiple parameters. Additionally, flow characteristics such as the quantification of inflow jets and the identification of multiple vortices led to correct predictions. CONCLUSIONS: MATCH compares state-of-the-art image-based blood flow simulation approaches to assess the rupture risk of IAs. Furthermore, this challenge highlights the importance of multivariate analyses by combining clinically relevant metadata with advanced morphological and hemodynamic quantification.