Shape-memory polymer (SMP) polyurethane foams have been applied as embolic devices and implanted in multiple animal models. These materials are oxidatively degradable and it is critical to quantify and characterize the degradation for biocompatibility assessments. An image-based method using high-resolution and magnification scans of histology sections was used to estimate the mass loss of the peripheral and neurovascular embolization devices (PED, NED). Detailed analysis of foam microarchitecture (i.e., struts and membranes) was used to estimate total relative mass loss over time. PED foams implanted in porcine arteries showed a degradation rate of ~0.11% per day as evaluated at 30-, 60-, and 90-day explant timepoints. NED foams implanted in rabbit carotid elastase aneurysms showed a markedly faster rate of degradation at ~1.01% per day, with a clear difference in overall degradation between 30- and 90-day explants. Overall, membranes degraded faster than the struts. NEDs use more hydrophobic foam with a smaller pore size (~150–400 μm) compared to PED foams (~800–1200 μm). Previous in vitro studies indicated differences in the degradation of the two polymer systems, but not to the magnitude seen in vivo. Implant location, animal species, and local tissue health are among the hypothesized reasons for different degradation rates.

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Study: Ventricular assist devices (VADs) provide cardiac support to failing hearts. A recent study showed that over half of VAD inflow cannulas are malpositioned; this number is estimated to be greater in patients with congenital heart defects. VAD malpositioning can lead to thrombus formation (clotting), pump failure, or even patient death. The relationship between VAD inflow cannula configuration and thrombus formation was explored for a pediatric patient with a single systemic ventricle. Methods: A post-Fontan hypoplastic left heart syndrome pediatric patient was evaluated. Computational fluid dynamics (CFD) was used to investigate the potential for thrombus formation in the apical vs. diaphragmatic inflow cannula configurations. A dynamic, non-Newtonian Carreau model was used and thrombogenic potential was defined by fluid with low velocity, low strain, and long residence times. CFD was validated using particle image velocimetry (PIV) and a mock circulatory loop with a moving ventricular sac. Results: While regions with thrombogenic potential were found in both the diaphragmatic and apical cannula configurations, the apical position exhibited a greater volume of fluid with these characteristics. PIV also confirmed these results. Conclusions: Although low velocity, low strain, long residence time flow may be indicative of thrombogenic potential, many factors actually contribute to thrombus formation and should be taken into account when comparing VAD implant configurations. Furthermore, while PIV validated overall trends observed in CFD, specific numerical values differed, suggesting the need for future refinement of both the CFD and PIV models.

Originality: Intravascular occlusion devices are an option in the occlusion of aneurysms, vascular anomalies, fistulas or tortuous vessels. The purpose of this study is to compare the vascular occlusion properties and assess overall healing of two occlusion devices: Shape Memory Medical TrelliX Embolic coil (TrelliX; test) and an approved HydroCoil device (control). Methods: TrelliX embolic coils and an approved hydrocoil device were implanted in selected vessels of 8 pigs. Vessels were explanted and processed for plastic histology. Transmission electron microscopy (TEM) was performed on representative blocks to compare the healing of the extracellular matrix. Results: At the 30-day timepoint functional occlusion was apparent in 24/30 Test vessels and 2/18 Control vessels while at the 90-days, 19/30 Test vessels and 5/18 Control vesses were occluded using 75% occlusion as the criteria for functional occlusion. In both devices, macrophages within the vessel and draining lymph nodes contain intracytoplasmic, eosinophilic particles. Vascular particles were electron dense on TEM and were intrahistiocytic, extracellular, and within rare polymorphonuclear cells in areas adjacent to polymer/biogel degeneration. The extracellular matrix was consistent with a progressive healing process between the two time points and was adjacent to the biogel/polymer and the electron dense particles. Conclusion: Overall Test and Control articles show a similar progression toward healing, with significantly more occlusion in the Test article. Changes in the polymer/biogel of both Control and Test articles is suggestive of degradation, and the eosinophilic particles are believed to be degradation biomaterial products. These degradation products were within the vessel and draining lymph node, and due to the location of these particles, within a healthy healing matrix, show no evidence of toxic or inflammatory effect.