【Introduction】
The patient-specific vascular models produced by 3D printing can provide more accurate anatomical information, which is useful for simulating complex vascular surgeries. Currently, due to the lack of understanding of this technology, its application is limited. This study provides an easy-to-follow and cost-effective guide to help readers understand the 3D-printed vascular anatomical models.

source:Coles-Black J, Bolton D, Chuen J. Accessing 3D Printed Vascular Phantoms for Procedural Simulation. Front Surg. 2021 Jan 27;7:626212. doi: 10.3389/fsurg.2020.626212. PMID: 33585550; PMCID: PMC7873568.


【Overview】
3D Printed Vascular Model
3D printing is a manufacturing technology that has gained significant attention in the field of surgery in recent years. This is because it can quickly create patient-specific anatomical models for surgical simulation and training. This convenient technology can convert images into physically usable models specific to the patient within the hospital, enabling surgeons and other surgical personnel to quickly obtain patient-specific anatomical structure models of the same scale as the real ones, thereby achieving better visualization and surgical planning.

Abdominal Aortic Aneurysm
Abdominal aortic aneurysm (AAA) refers to the dilation of the abdominal aorta to at least 1.5 times its normal size, or an outer diameter of 3 centimeters. As a true aneurysm, the dilation affects all three layers of the aortic wall, namely the intima, media, and adventitia.

The infrarenal abdominal aorta is the most common site of occurrence for abdominal aortic aneurysms and is also the most suitable anatomical structure for repair. It can be repaired through endovascular interventional therapy (EVAR) or open surgery with renal infrarenal aorta occlusion. Modern endovascular interventional techniques have made significant progress, and EVAR has become the standard treatment method for patients with suitable anatomical structures.

However, when treating patients with AAA anatomy that exceeds the standard, vascular surgeons and interventional radiologists must adjust their treatment plans. If the aneurysm extends to the renal artery orifice but does not involve it, it is called a pararenal abdominal aortic aneurysm. If the aneurysm further extends upwards and involves the renal artery and visceral arteries, it is called a pararenal or visceral pararenal abdominal aortic aneurysm. Performing endovascular repair for these complex anatomical structures is extremely challenging and may be impossible with current technical capabilities.

The Application of 3D Printing Models in AAA Simulation
As vascular surgery continues to shift towards minimally invasive techniques, the application scope of EVAR has expanded significantly, and the repair of complex abdominal aortic aneurysms (AAA) has become increasingly challenging. EVAR is prone to complications such as internal leakage, graft occlusion, displacement, and infection, requiring secondary interventions and increasing medical costs. By using patient-specific 3D printed AAA models, the anatomical structure can be visually presented, the graft can be accurately selected, and the difficulties during the operation can be predicted, thereby reducing complications. At the same time, 3D printed EVAR simulators have significant value in vascular surgeon training, which can enhance the trainees' confidence in operation and practical skills, shorten the operation and fluoroscopy time, and reduce the amount of contrast agent used. In the current context of reduced clinical practice opportunities and restricted traditional apprenticeship training, simulation training based on 3D printed models has become an efficient and feasible teaching solution.


【3D Printing Technology】
For vascular interventional physicians, the most readily available 3D printing technologies include those that can be obtained through university collaborations, as well as those that are affordable, compact in size, and suitable for placement within hospitals. The most common 3D printing methods include fused deposition modeling (FDM), stereolithography (SLA), and inkjet printing technology.

For those who are interested in trying this technology, fused deposition modeling (FDM) is the easiest to get started with among 3D printing techniques, with a retail price as low as a few hundred dollars. This technology builds models layer by layer by extruding heated and softened polymers. Common materials include rigid thermoplastic polymers such as acrylonitrile-butadiene-styrene copolymer (ABS), polylactic acid (PLA), and flexible thermoplastic materials such as thermoplastic polyurethane (TPU) and thermoplastic elastomers (TPE), the latter being a soft rubber-like filament. FDM has been used for 3D printing surgical guides, patient-specific anatomical models for preoperative simulation, and even for printing customized drugs with individualized dosages for patients.

SLA technology utilizes ultraviolet lasers to selectively scan containers containing photosensitive polymers, curing and solidifying specific areas of the liquid surface. As the process progresses, the final object is built layer by layer. Currently, SLA technology has been applied in preoperative simulation and training for anatomical modeling, as well as in the construction of tissue engineering scaffolds.

Inkjet 3D printing is an extension of the traditional two-dimensional paper printing technology. Hundreds of micro nozzles selectively deposit light-sensitive polymer droplets layer by layer and use ultraviolet light for rapid curing. Inkjet printing equipment can cost up to several hundred thousand dollars, making it the most expensive 3D printing technology known so far. Therefore, in the initial stage, it needs to be collaborated with academic institutions until its cost is rationalized. This technology can 3D print multiple anatomical structures at once, enabling the basic distinction of different tissues for simulation research.


【Discussion】
Despite the material limitations, the AAA models 3D-printed using multiple 3D printing technologies can successfully simulate the catheterization and implantation challenges encountered in actual vascular surgeries. As the size and material characterization effectiveness improve, these models are expected to become a powerful auxiliary tool for the planning of complex EVAR surgical procedures.

Core Strengths: 

Convenient and efficient: The products can be independently manufactured within the hospital. They can be transformed from the laboratory to clinical application within a few hours, without relying on external suppliers. This saves time and costs. 

Precise personalization: Perfectly reconstructs the patient's vascular anatomical structure, especially suitable for preoperative planning of complex cases, reducing surgical risks; 

Multi-scenario compatibility: Suitable for surgical simulation, medical training, and patient education, with high cost-effectiveness.

Limitations: 

Equipment and skill requirements: Initial investment is needed to purchase printers, and medical staff only need to learn the software operation briefly. 

Material limitations: Low-cost printers are unable to produce models that perfectly replicate the tactile sensation of real blood vessels, and there is still room for improvement in terms of visual fidelity. 

Error risk: The quality of CT images, the segmentation process, and the printing procedure may all introduce minor errors. Standardized operations are necessary to minimize deviations.

【Conclusion】

Once the challenges in developing this workflow are overcome, 3D printed anatomical models will become a routine tool in the complex surgical planning of our vascular surgery center and the entire surgical department. It has been proven that the specific patient-based models are a valuable complement to standard imaging examinations and help with the rehearsal and adjustment of surgical instruments before the operation. When planning the surgical approach for complex abdominal aortic aneurysms (AAA), the hollow flexible models are particularly useful for the rehearsal of stent implantation and positioning via the iliac artery approach, as well as for predicting the trajectories of guidewires and instruments. 

With the increasing popularity of 3D printing technology, its application in preoperative simulation is bound to thrive.