Engineering Additive Manufacturing and Molding Techniques to Create Lifelike Willis' Circle Simulators with Aneurysms for Training Neurosurgeons

Abstract

Neurosurgeons require considerable expertise and practical experience in dealing with the critical situations commonly encountered during difficult surgeries; however, neurosurgical trainees seldom have the opportunity to develop these skills in the operating room. Therefore, physical simulators are used to give trainees the experience they require. In this study, we created a physical simulator to assist in training neurosurgeons in aneurysm clipping and the handling of emergency situations during surgery. Our combination of additive manufacturing with molding technology, elastic material casting, and ultrasonication-assisted dissolution made it possible to create a simulator that realistically mimics the brain stem, soft brain lobes, cerebral arteries, and a hollow transparent Circle of Willis, in which the thickness of vascular walls can be controlled and aneurysms can be fabricated in locations where they are likely to appear. The proposed fabrication process also made it possible to limit the error in overall vascular wall thickness to just 2-5%, while achieving a Young's Modulus closely matching the characteristics of blood vessels (~5%). One neurosurgical trainee reported that the physical simulator helped to elucidate the overall process of aneurysm clipping and provided a realistic impression of the tactile feelings involved in this delicate operation. The trainee also experienced shock and dismay at the appearance of leakage, which could not immediately be arrested using the clip. Overall, these results demonstrate the efficacy of the proposed physical simulator in preparing trainees for the rigors involved in performing highly delicate neurological surgical operations.

Keywords: additive manufacturing; and dissolution; aneurysm clipping surgery practice; fully transparent and elastic vascular Simulator; molding; neurosurgeon surgical simulator.

Figure 1

A layout of the Circle of Willis vascular system, showing the obvious differences in the outer diameter (D), inner diameter (d), and wall thickness (t) in various locations.

Figure 2

(a) The two outer (clamshell) molds fabricated using a commercial 3D printer (Objet30 Dental Prime, Stratasys) with a biocompatible material (MED 610, Stratasys); (b) the inner wax mold fabricated using a commercial 3D printer (Projet 3500 CPX Max, 3D Systems) with a wax material (Visijet Hi-Cast, 3D Systems); (c) PDMS was slowly injected into the gap between the molds until the gap was completely filled; (d) the PDMS casting (with inner mold still intact) following removal of the outer molds; (e) dissolution of the inner wax mold was facilitated using ultrasonication, as reported previously [23]; (f) the resulting Circle of Willis with major corresponding arteries.

Figure 3

(a) The overall 3D-printed skull; (b) how a piece of cranium located on the right side of the forehead can be removed to simulate a craniotomy.

Figure 4

(a) A mold of the left frontal lobe printed using a 3D printer (Fortus 360mc, Stratasys); (b,c) the acrylonitrile butadiene styrene (ABS) mold was fixed within a transparent box into which silicon was poured to create a cast; (d) the ABS mold was sliced open using a knife and then peeled back to remove the ABS mold; (e) a mixture of pink jelly was poured into the cavity; (f) a realistic model of the frontal lobe was created.

Figure 5

(a) The circulatory system, which included two pumps and several beakers; (b) the overall system specifically for practicing the clipping of aneurysms during surgery.

Figure 6

The five tubes were connected to the pumping system with pieces of papers marked with the letter “A” placed beneath. This experiment clearly illustrates the differences in transparency among the five tubes.

Figure 7

(a) The tensile test results of specimens fabricated using different ratios of silicone base and hardener (10:1 to 20:1); (b) enlarged area of (a), and the Young’s Modulus corresponding to different ratios was estimated from the slopes of each curve.

Figure 8

The transparency of the various tubes used to simulate blood vessels. Obviously, the letter “A” appears more clearly through Tube 1, which was fabricated using the method proposed in Section 3.2.

Figure 9

(a) An experienced neurosurgeon (Dr. Liu from our research team) gave a neurosurgical trainee instructions on the use of the proposed simulator to practice clipping aneurysms; (b) the overall procedure involved a craniotomy followed by the use of surgical forceps to make space between the brain lobes in order to locate the aneurysm; (c) based on observations of yellow liquid leaking from the area of interest, the trainee determined that the aneurysm had ruptured. Despite initial efforts to clip the aneurysm, the leakage continued; (d) efforts to re-clip the aneurysm under the guidance of Dr. Liu succeeded in stopping the leakage.