Research Article: On the optimization of low-cost FDM 3D printers for accurate replication of patient-specific abdominal aortic aneurysm geometry

Date Published: January 17, 2018

Publisher: Springer International Publishing

Author(s): Michael Chung, Norbert Radacsi, Colin Robert, Edward D. McCarthy, Anthony Callanan, Noel Conlisk, Peter R. Hoskins, Vasileios Koutsos.

http://doi.org/10.1186/s41205-017-0023-2

Abstract

There is a potential for direct model manufacturing of abdominal aortic aneurysm (AAA) using 3D printing technique for generating flexible semi-transparent prototypes. A patient-specific AAA model was manufactured using fused deposition modelling (FDM) 3D printing technology. 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). Printing parameters were investigated to evaluate their effect on 3D–printing precision and transparency of the final model. ISO standard tear resistance tests were carried out on Ninjatek Cheetah specimens for a comparison of tear strength with silicone rubbers.

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 °C produced the most transparent results. 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). 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 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.

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.

The online version of this article (10.1186/s41205-017-0023-2) contains supplementary material, which is available to authorized users.

Partial Text

An 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 [1–3]. Rupture of the AAA has a fatality rate of 90% [4]. If diagnosed before rupture, patients with AAA are evaluated for elective surgical repair. Current clinical practice for rupture risk assessment is based on measurement of the diameter of the largest part of the aneurysm [2, 5]. In case the diameter exceeds a threshold value (5.5 cm for men, 5.0 cm for women), patients are considered for repair. If the diameter is less than the threshold patients are put on a screening program. Traditional AAA repair involves open surgery in which the aneurysm is surgically exposed and replaced with a graft which is connected to the aorta. Increasingly, AAA repair is performed using a less invasive procedure involving arterial puncture and the deployment of the graft by catheter. This is referred to as ‘endovascular aneurysm repair’ or EVAR [6]. 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). There are issues concerning surgical training in EVAR and in surgical planning for the individual patient. Approaches to surgical training and planning for EVAR include the use of virtual reality [7, 8] and experimental systems based on realistic models of AAA [9, 10]. It is the experimental systems which are of interest in the current paper and are further considered below.

This study aimed to produce a flexible and robust physical model of a patient-specific AAA to aid endovascular aneurysm repair education and planning in a time and cost-effective manner. The FDM 3D printing technique is a relatively fast and inexpensive way to manufacture an AAA model for a particular patient. Since CT scanning typically takes approximately 15 min [29], the total processing and manufacturing procedure could feasibly be done in less than 48 h. This is a significantly reduced time compared with that for lost wax casting procedures using CNC machined molds and other rapid prototyping procedures that require at least 2 weeks to manufacture a model [30].

This paper investigated fused deposition modelling (FDM) 3D printing method for manufacturing abdominal aortic aneurysm (AAA) physical models for rupture prediction and prevention. The Ultimaker 3 3D printer was used for rapid prototyping of a patient-specific AAA using a semi-transparent thermoplastic polyurethane filament together with a PVA filament, for water-soluble support structure generation. Experimentation with printing parameters found that an increase in printing nozzle temperature to 255 °C and an infill percentage of 100% increased the transparency while maintaining precision. Increasing printing speed was found to have a detrimental effect on precision, with a 90 mm/s speed yielding an 8.5% discrepancy between CAD and physical model wall thickness compared to an error lower than 0.01 mm when using a 30 mm/s printing speed.

 

Source:

http://doi.org/10.1186/s41205-017-0023-2

 

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