Cost of manufacture has also been high – shown to be between 6 EUR per model – due to requiring two sets of molds, for outer and inner geometry, and material waste. However, the time of manufacture has been high – with lead time upwards of 2 weeks. Casting of aneurysm phantoms is usually concerned with creation of geometrically accurate models from transparent silicone rubbers. Manufacturing techniques may be broadly divided between casting techniques and 3D printing. Physical models of aneurysms (both abdominal aortic and cerebral) have been manufactured for a variety of scientific purposes inclusion in experimental flow systems to study flow patterns and pressures for validation of rupture site prediction made using finite element analysis, for laboratory investigations of migration of stent grafts, and in experimental systems for simulation of interventional procedures.
It is the experimental systems which are of interest in the current paper and are further considered below. Approaches to surgical training and planning for EVAR include the use of virtual reality and experimental systems based on realistic models of AAA. There are issues concerning surgical training in EVAR and in surgical planning for the individual patient. Surgical repair by EVAR has a number of potential complications including migration of the graft and endoleaks (pooling of blood outside the graft within the excluded aneurysmal sac). This is referred to as ‘endovascular aneurysm repair’ or EVAR. Increasingly, AAA repair is performed using a less invasive procedure involving arterial puncture and the deployment of the graft by catheter. Traditional AAA repair involves open surgery in which the aneurysm is surgically exposed and replaced with a graft which is connected to the aorta. If the diameter is less than the threshold patients are put on a screening program. In case the diameter exceeds a threshold value (5.5 cm for men, 5.0 cm for women), patients are considered for repair.
Current clinical practice for rupture risk assessment is based on measurement of the diameter of the largest part of the aneurysm. If diagnosed before rupture, patients with AAA are evaluated for elective surgical repair. Rupture of the AAA has a fatality rate of 90%. It was concluded that the model would be of use in endovascular aneurysm repair planning and education, particularly for practicing placement of hooked or barbed stents, due to the model’s balance of flexibility, transparency, robustness and cost-effectiveness.Īn abdominal aortic aneurysm (AAA) involves the weakening and enlargement of the lower part of the aorta, due to the degradation of elastin in the arterial wall. The model had lower cost (4.50 GBP per model), shorter manufacturing time (25 h 3 min) and an acceptable level of accuracy (2.61% error) compared to other methods. The tear resistance test found Ninjatek Cheetah TPU to have an average tear resistance of 83 kN/m, higher than any of the silicone rubbers used in previous AAA model manufacture. The model had fair transparency, allowing external inspection of model inserts such as stent grafts, and good flexibility with an overall discrepancy between CAD and physical model average wall thicknesses of 0.05 mm (2.5% thicker than the CAD model). It was found that an increase in printing speed decreased printing accuracy, whilst using an infill percentage of 100% and printing nozzle temperature of 255 ☌ produced the most transparent results.
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ISO standard tear resistance tests were carried out on Ninjatek Cheetah specimens for a comparison of tear strength with silicone rubbers. Printing parameters were investigated to evaluate their effect on 3D–printing precision and transparency of the final model. A flexible, semi-transparent thermoplastic polyurethane (TPU), called Cheetah Water (produced by Ninjatek, USA), was used as the flexible, transparent material for model manufacture with a hydrophilic support structure 3D printed with polyvinyl alcohol (PVA). A patient-specific AAA model was manufactured using fused deposition modelling (FDM) 3D printing technology. There is a potential for direct model manufacturing of abdominal aortic aneurysm (AAA) using 3D printing technique for generating flexible semi-transparent prototypes.
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