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OBJECTIVE The development of new endovascular technologies and techniques for mechanical thrombectomy in stroke has greatly relied on benchtop simulators. This paper presents an affordable, versatile, and realistic benchtop simulation model for stroke. METHODS A test bed for embolic occlusion of cerebrovascular arteries and mechanical thrombectomy was developed with 3D-printed and commercially available cerebrovascular phantoms, a customized hydraulic system to generate physiological flow rate and pressure, and 2 types of embolus analogs (elastic and fragment-prone) capable of causing embolic occlusions under physiological flow. RESULTS The test bed was highly versatile and allowed realistic, radiation-free mechanical thrombectomy for stroke due to large-vessel occlusion with rapid exchange of geometries and phantom types. Of the transparent cerebrovascular phantoms tested, the 3D-printed phantom was the easiest to manufacture, the glass model offered the best visibility of the interaction between embolus and thrombectomy device, and the flexible model most accurately mimicked the endovascular system during device navigation. None of the phantoms modeled branches smaller than 1 mm or perforating arteries, and none underwent realistic deformation or luminal collapse from device manipulation or vacuum. The hydraulic system created physiological flow rate and pressure leading to iatrogenic embolization during thrombectomy in all phantoms. Embolus analogs with known fabrication technique, structure, and tensile strength were introduced and consistently occluded the middle cerebral artery bifurcation under physiological flow, and their interaction with the device was accurately visualized. CONCLUSIONS The test bed presented in this study is a low-cost, comprehensive, realistic, and versatile platform that enabled high-quality analysis of embolus–device interaction in multiple cerebrovascular phantoms and embolus analogs.

Introduction Cerebrovascular test beds for large vessel occlusion (LVO) stroke are widely used to evaluate and develop new thrombectomy technologies and strategies. Most of the studies on test beds described the fabrication of the cerebrovascular phantoms but not the flow circuit and clot analogs, which are essential components to replicate LVO in patients with stroke. In addition, cerebrovascular phantoms are made from different materials and techniques and may result in different and biased testing results. However, such comparison has not been studied. We describe in detail the construction of a cerebrovascular test bed for stroke and compare the advantages and disadvantages of different types of cerebrovascular phantoms. Materials and Methods The testing platform for thrombectomy was developed with three components: 1) cerebrovascular phantom, 2) hydraulic system, and 3) clot analogs. For the cerebrovascular phantom, patient-specific cerebrovasculature was reconstructed and three types of phantoms were fabricated: 3D-printed resin, glass, and silicone. For the hydraulic system, a syringe pump, tubing and variable flow resistors were connected to the phantoms to replicate intraluminal pulsatile physiologic flow rate and pressure. For the clot analogs, human blood-derived red blood cells and plasma were mixed to make two types of clot analogs: elastic and fragment-prone. To evaluate the performance of the test bed and compare the three types of phantoms, LVO was replicated in the phantom and thrombectomy procedures using the ADAPT and CAPTIVE techniques were performed by two experienced neurointerventionalists. Results The 3D-printed phantom is the least expensive and fastest to fabricate, allowing rapid iterations to refine the geometries to make the glass and silicone phantoms. The glass phantom is easier to navigate compared to equivalent anatomy in patients and has the best visualization of the device-clot interaction. The silicone phantom provides the most accurate haptic representation of the navigation of thrombectomy devices in patients, deforming and moving when forces are applied by the device. However, the silicone phantom wall is still significantly more resistant than cerebral arteries and tolerates forces and movements that would be deemed unsafe in clinical situations without tearing. The test bed can generate physiologically realistic pressure. Accurate physiologic pressures with pulsatile waveforms were generated to simulate normotensive (120/80 mmHg) and hypertensive (147/85 mmHg) status. The pressure can be adjusted by the variable flow resistors and tubing length. The clot analogs can be embolized under physiologic flow and consistently lodged at the MCA bifurcation of the cerebrovascular phantoms. Conclusion The test bed presented in this study is a low-cost, comprehensive, realistic, and versatile platform that enabled high-quality analysis of clot-device interaction. Disclosures Y. Liu: None. A. Reddy: None. J. Cockrum: None. D. Gebrezgiabhier: None. E. Davis: None. Y. Zheng: None. A. Pandey: None. A. Shih: None. L. Savastano: 4; C; Endovascular Engineering.

Introduction Mechanical thrombectomy using a suction catheter, a stent or the combination of both has recently become a standard of care for large vessel occlusion (LVO) stroke. However, complete recanalization (mTICI=3) with the best neurological outcome can be achieved in only 50% of the cases. In addition, multiple devices and passes are usually needed to recanalize, prolonging procedure times, increasing the risks of vessel damage. To improve our understanding of the interaction between the embolus and thrombectomy devices, in this study we first created a test bed of LVO and analyzed the forces during recanalization. We provided mechanistic explanations of the observations and failure modes by mechanically characterizing a range of emboli retrieved from patients with LVO stroke. Materials and Methods An LVO test bed with anatomically accurate glass model of an MCA bifurcation was created with physiological flow and pressure. Thrombectomy procedures to remove embolus analogs (EAs) were performed 10 times each using the ADAPT and CAPTIVE techniques. The mechanical responses of the EAs to the action of the thrombectomy devices were recorded and analyzed and deemed to be mostly due to tensile load. To quantify the tensile properties of emboli, 37 emboli retrieved from 20 patients were collected and tested on a customized tensile test machine. The machine applied uniaxial tensile load to the emboli to mimic the vacuum suction and stent pull during thrombectomy procedure. The elongation, thinning, and dissociation were quantified to calculate the embolus strength, represented by ultimate strain (maximum elongation) and ultimate stress (maximum force per unit cross-sectional area). Results The forces involved in the embolus removal process were categorized into: 1) retrieval forces including vacuum suction or stent pull, 2) resistance forces including static friction and adhesion at the embolus-vascular interface, the preload of the embolus protruding into branching arteries, and the pressure difference proximal and distal to the embolus, and 3) emboligenic forces including dynamic friction at the embolus-vascular interface and the blood pressure and shear at the embolus interface. In order to remove emboli, retrieval forces need to be larger than the resistance forces. If the retrieval force is larger than the strength of the embolus, the embolus will undergo multistage fracture, leading to embolization. The tensile testing of patients’ emboli revealed similar behavior, including elongation under tension and multi-stage fracture patterns. The ultimate strain ranged from 1.05 to 4.89 (2.41 ± 1.04 [mean ± SD]) and the ultimate stress ranged from 63 to 2396 kPa (569 ± 695 kPa). The ultimate strain of the emboli increased with a higher platelet percentage, and the ultimate stress increased with a higher fibrin percentage and decreased with a higher red blood cell percentage. Conclusion Suction catheters and the stents recanalize by applying tensile force to dislodge and remove the emboli. The tensile force leads to embolus elongation and thinning until dissociation, which may cause iatrogenic embolization. The ability to resist dissociation is determined by embolus strength, which significantly correlates with composition and varies within and among patients and within the same embolus. Disclosures Y. Liu: None. Y. Zheng: None. A. Reddy: None. D. Gebrezgiabhier: None. E. Davis: None. J. Cockrum: None. J. Gemmete: None. N. Chaudhary: None. J. Griauzde: None. A. Pandey: None. A. Shih: None. L. Savastano: 4; C; Endovascular Engineering.

OBJECTIVEThis study’s purpose was to improve understanding of the forces driving the complex mechanical interaction between embolic material and current stroke thrombectomy devices by analyzing the histological composition and strength of emboli retrieved from patients and by evaluating the mechanical forces necessary for retrieval of such emboli in a middle cerebral artery (MCA) bifurcation model.METHODSEmbolus analogs (EAs) were generated and embolized under physiological pressure and flow conditions in a glass tube model of the MCA. The forces involved in EA removal using conventional endovascular techniques were described, analyzed, and categorized. Then, 16 embolic specimens were retrieved from 11 stroke patients with large-vessel occlusions, and the tensile strength and response to stress were measured with a quasi-static uniaxial tensile test using a custom-made platform. Embolus compositions were analyzed and quantified by histology.RESULTSUniaxial tension on the EAs led to deformation, elongation, thinning, fracture, and embolization. Uniaxial tensile testing of patients’ emboli revealed similar soft-material behavior, including elongation under tension and differential fracture patterns. At the final fracture of the embolus (or dissociation), the amount of elongation, quantified as strain, ranged from 1.05 to 4.89 (2.41 ± 1.04 [mean ± SD]) and the embolus-generated force, quantified as stress, ranged from 63 to 2396 kPa (569 ± 695 kPa). The ultimate tensile strain of the emboli increased with a higher platelet percentage, and the ultimate tensile stress increased with a higher fibrin percentage and decreased with a higher red blood cell percentage.CONCLUSIONSCurrent thrombectomy devices remove emboli mostly by applying linear tensile forces, under which emboli elongate until dissociation. Embolus resistance to dissociation is determined by embolus strength, which significantly correlates with composition and varies within and among patients and within the same thrombus. The dynamic intravascular weakening of emboli during removal may lead to iatrogenic embolization.

Background As access to patient emboli is limited, embolus analogs (EAs) have become critical to the research of large vessel occlusion (LVO) stroke and the development of thrombectomy technology. To date, techniques for fabricating standardized human blood-derived EAs are limited in the variety of compositions, and the mechanical properties relevant to thrombectomy are not quantified. Methods EAs were made by mixing human banked red blood cells (RBCs), plasma, and platelet concentrate in 10 different volumetric percentage combinations to mimic the broad range of patient emboli causing LVO strokes. The samples underwent histologic analysis and tensile testing to mimic the pulling action of thrombectomy devices, and were compared to patient emboli. Results EAs had histologic compositions of 0-96% RBCs, 0.78%-92% fibrin, and 2.1%-22% platelets, which can be correlated with the ingredients using a regression model. At fracture, EAs elongated from 81% to 136%, and the ultimate tensile stress ranged from 16 to 949 kPa. These EAs’ histologic compositions and tensile properties showed great similarity to those of emboli retrieved from LVO stroke patients, indicating the validity of such EA fabrication methods. EAs with lower RBC and higher fibrin contents are more extensible and can withstand higher tensile stress. Conclusions EAs fabricated and tested using the proposed new methods provide a platform for stroke research and pre-clinical development of thrombectomy devices.

Our understanding and management of carotid artery disease has largely relied on angiography, US and MR. However, existing modalities cannot accurately identify the spectrum of thrombogenic lesions on the vascular surface or reliably detect structural markers of instability. Thus, the natural history of the different histopathological hallmarks of advanced or complicated plaques is unknown, and many patients with culprit substenotic plaques are misdiagnosed with cryptogenic stroke. An intraluminal approach to directly inspect the endovascular surfaces at unprecedented resolutions would enable detailed structural analysis of carotid plaques and the identification of the root cause of carotid-related strokes. A scanning fiber angioscope (SFA), a high-definition 1.2-mm forward-viewing camera that generates videos by spirally scanning low-power laser beams, was developed for clinical use and employed to analyze the endovascular surfaces of ex vivo human carotid arteries (n=95) and endarterectomized plaques (n=20). Specimens were then imaged with US and micro-CT, and all vascular diagnostic tests obtained in the patients undergoing carotid revascularization were accessed. Imaging findings in the vascular surfaces were then validated by histomorphological analysis of >300 lesions, and an angioscopic classifier for atherosclerosis was generated. Full-color videos at 30Hz and at a resolution >200,000 pixels were generated from the entire endovascular circumference in all specimens with depth-of-focus larger than 5cm in saline solution. The ability to analyze the surface anatomy with unparalleled detail allowed the identification of early, intermediate, advanced and complex atherosclerotic lesions, including ulceration of fibrotic cap, excavation of the necrotic core leading to pseudolumens, intimal flaps, exposed necrotic core to the lumen, erosions, recent and remote intimal hemorrhages, luminal thrombus, eruptive calcified nodules and calcified intimal sheaths and plates. SFA offers a direct view of the endoluminal surfaces with unparalleled resolution and has the potential to revolutionize research, diagnosis, prognosis and image-guided therapy in carotid atherosclerosis.

Background Context Growing rod constructs are an important contribution for treating patients with early-onset scoliosis. These devices experience high failure rates, including rod fractures. Purpose The objective of this study was to identify the failure mechanism of retrieved growing rods, and to identify differences between patients with failed and intact constructs. Study Design/Setting Growing rod patients who had implant removal and were previously enrolled in a multicenter registry were eligible for this study. Patient Sample Forty dual-rod constructs were retrieved from 36 patients across four centers, and 34 of those constructs met the inclusion criteria. Eighteen constructs failed due to rod fracture. Sixteen intact constructs were removed due to final fusion (n=7), implant exchange (n=5), infection (n=2), or implant prominence (n=2). Outcome Measures Analyses of clinical registry data, radiographs, and retrievals were the outcome measures. Methods Retrievals were analyzed with microscopic imaging (optical and scanning electron microscopy) for areas of mechanical failure, damage, and corrosion. Failure analyses were conducted on the fracture surfaces to identify failure mechanism(s). Statistical analyses were performed to determine significant differences between the failed and intact groups. Results The failed rods fractured due to bending fatigue under flexion motion. Construct configuration and loading dictate high bending stresses at three distinct locations along the construct: (1) mid-construct, (2) adjacent to the tandem connector, or (3) adjacent to the distal anchor foundation. In addition, high torques used to insert set screws may create an initiation point for fatigue. Syndromic scoliosis, prior rod fractures, increase in patient weight, and rigid constructs consisting of tandem connectors and multiple crosslinks were associated with failure. Conclusion This is the first study to examine retrieved, failed growing rod implants across multiple centers. Our analysis found that rod fractures are due to bending fatigue, and that stress concentrations play an important role in rod fractures. Recommendations are made on surgical techniques, such as the use of torque-limiting wrenches or not exceeding the prescribed torques. Additional recommendations include frequent rod replacement in select patients during scheduled surgeries.