Real Stiffness and Vividness Reproduction of Anatomic Structures Into the 3-Dimensional Printed Models Contributes to Improved Simulation and Training in Skull Base Surgery

Abstract

BACKGROUND:

Despite the advancement of 3-dimensional (3D) printing technology with medical application, its neurosurgical utility value has been limited to understanding the anatomy of bones, lesions, and their surroundings in the neurosurgical field.

OBJECTIVE:

To develop a 3D printed model simulating the surgical technique applied in skull base surgery (SBS), especially to reproduce visually the surgical field together with the mechanical properties of tissues as perceived by the surgeon through procedures performance on a model.

METHODS:

The Young modulus representing the degree of stiffness was measured for the tissues of anesthetized animals and printing materials. The stiffness and vividness of models were adjusted appropriately for each structure. Empty spaces were produced inside the models of brains, venous sinuses, and tumors. The 3D printed models were created in 7 cases of SBS planned patients and were used for surgical simulation.

RESULTS:

The Young modulus of pig's brain ranged from 5.56 to 11.01 kPa and goat's brain from 4.51 to 13.69 kPa, and the dura of pig and goat values were 14.00 and 24.62 kPa, respectively. Although the softest printing material had about 20 times of Young modulus compared with animal brain, the hollow structure of brain model gave a soft sensation resembling the real organ and was helpful for bridging the gap between Young moduli values. A dura/tentorium-containing model was practical to simulate the real maneuverability at surgery.

CONCLUSION:

The stiffness/vividness modulated 3D printed model provides an advanced realistic environment for training and simulation of a wide range of SBS procedures.

ABBREVIATIONS:

ATPA

anterior transpetrosal approach

BA

basilar artery

CC

cochlea

FC

fallopian canal

FLA

far lateral approach

IAC

internal auditory canal

PCA

posterior cerebral artery

PICA

posterior inferior cerebellar artery

PTPA

posterior transpetrosal approach

SBS

skull base surgery

SCA

superior cerebellar artery

SCTA

supracerebellar transtentorial approach

SPS

superior petrosal sinus

SS

sigmoid sinus

STL

stereolithography

TCA

transcondylar approach

TPA

transpetrosal approach

TS

transverse sinus

VA

vertebral artery.

Neurosurgeons usually gain insight into normal and abnormal structure and function, designing next a surgical strategy on two-dimensional computed tomography (CT) or MRI. Since current surgical procedures, particularly in skull base surgery (SBS), have complex design to obtain a high quality of outcome and preserving important function, the demand of advanced visualization has brought virtual reality 3-dimensional (3D) computer graphics into use.^1-3 Furthermore, the recently developed 3D printing technology has applications spanning out from the industrial to the medical field.^4-6 In this context, they have been applied for simulation of mastoidectomy,^7,8 transnasal endoscopic surgery,⁹ planning of clipping/embolization of cerebral aneurysms,^10-14 preoperative simulation of glioma surgery,¹⁵ and analysis of SBS approaches.^16,17

SBS contains some of the most difficult surgical techniques that require extraordinary skills. Young neurosurgeons must achieve professional technique through repetitive training by assisting mentors at surgery and cadaver dissection. The application of 3D printed models could be of special interest both for specialists and aspiring young neurosurgeons with their realistic appearance that would allow to practice drilling, peeling, retracting, exposing, and cutting of anatomic structures. However, existing 3D printed models have limited number of anatomic structures, often recreating only bone anatomy, lesions, and the surrounding neurosurgical field.¹⁶ Limitations appear in the difficulties to recreate mechanical properties using conventional printing methods because information about those of organs is insufficient. The limited variety of materials^9,18 leads to difficulty of stiffness adjustment of particularly soft intracranial structures.^7,11,19

In this study, we aimed to evaluate the potential of the 3D printed model in which stiffness/vividness of color were adequately modified for simulation and training in SBS. Initially, we analyzed physical properties of animal organs and printing materials. The 3D printing method and material selection were adjusted appropriately for each intracranial structure to create a realistic practical 3D printed model. The completed novel models were applied for simulation and training toward certain surgical procedures and allowed more precise presurgical planning and realistic training for SBS procedures.

METHODS

Animal Surgery and Young Modulus Measurement

The protocol of animal experiments was approved by the Institutional Animal Care and Use Committee of our University (No. 2021-024 and No. 2021-035). A wide bilateral craniotomy in anesthetized pigs and goats was followed by an extensive dura matter resection. A tuning fork type softness sensor, SOFTGRAM (Shinko Denshi), was used for measurement of the Young modulus, which represents the tensile or compressive stiffness of a linear elastic body. The Young modulus was measured on the brain surface and the resected and folded up to 5 mm thickness dura matter (because of device's technical requirement).

Segmentation Process of Anatomic Structures in Digital Images

Digital Imaging and Communications in Medicine data of CT, CT angiography, CT venography, heavy T2-weighted MRI, and gadolinium-enhanced MRI of each patient were merged for image analysis by Amira 5.6 (FEI Company). Segmentation was performed for labeling each pixel according to its attribution to specific anatomic structure, and data were converted to stereolithography (STL) data.

Print Materials and 3D Printing

An elastic resin, Agilus-Clear (Stratasys Ltd), and vivid hard resins,Vero Pure White, Vero Magenda Vivid, Vero Cyan Vivid, Vero Yellow Vivid and Vero Clear (all Stratasys Ltd), were used in the Stratasys J750 printer (Stratasys Ltd) A molding material was made by mixing both resins (Supplemental Table, http://links.lww.com/ONS/A858). The increased mixing ratio of vivid hard resins elevated the Shore-A scale value (quantifies relative stiffness and vividness). The Young modulus and Shore-A scale were measured 3 times each on cuboid material samples (size: 30 × 30 × 10 mm). Shore-A scale was measured by an American Society for Testing and Materials D2240 type A durometer—GS-719 (TECLOCK). The STL data of all structures were imported into a 3D printing software—GrabCAD Print (Stratasys Ltd), which allows to select the Shore-A scale and color of structures for printing. Other extremely soft molding materials, Solid Internal Organs Fiber Contraction-1 (ExS-10A) and Solid Internal Organs Fiber Contraction-4 (ExS-15A), were used in the Stratasys J750DAP (all Stratasys Ltd.).

Excavation of Hollow Models

The STL data of the model were rewritten at the segmentation process as a hollow structure with a wall thickness about 3 to 5 mm. When the 3D printed model was created, the hollow part was filled with support material that could be easily removed by suction-evacuation through a small corridor.

Patient Selection and Surgical Simulation with the 3D Printed Model

All patients gave written informed consent in accordance with the Declaration of Helsinki; study approval was obtained from the Institutional Review Board of our university (Trial registration ID: 32-105, 10181). Seven cases of SBS planned procedures in this hospital were selected as subjects for creating 3D printed models. The completed models were applied for surgical simulation and training. After discussion about the surgical strategy, a 3D printed model immobilized by spring clamps was dissected by a neurosurgeon using a surgical microscope—ZEISS OPMI PENTERO 900 (Carl Zeiss Meditec AG), standard neurosurgical instruments and a high-speed drill—Midas Rex Integrated Power Console System (Medtronic Inc) and microspeed uni (Aesculap AG).

RESULTS

The Young Modulus of Animal Tissues

Young modulus was measured on the brain surface with intact pia matter and without major blood vessels in an anesthetized pig (Figure 1A) and goat (Figure 1B). The average of 15 measurements at 4 brain regions was calculated. The averages of the Young modulus of pig's brain were 5.56 to 11.01 kPa and those of goat were 4.51 to 13.69 kPa (Figure 1A and 1B). The resected dura Young modulus was measured 50 times, and the averages in pig and goat (Figure 1C) were 14.00 and 24.62 kPa, respectively.

FIGURE 1.

The Young modulus value of a A, pig brain and B, goat brain were measured 15 times each, and their C, dura matter was measured 50 times each. Numbers and arrow marked on the photos are representing the regions of measurement. Numbers on the graphs are showing the averages of each region.

Analyses of Material Properties and 3D Printing Procedure

To select a suitable material for each anatomic structure, the Young modulus was measured on the cuboid material samples 3 times each, and the averages ranged 223 to 3745 kPa, being higher than the brain and dura (Supplemental Table, http://links.lww.com/ONS/A858). Even the softest material, ExS-10A (Shore-A = 10), had about 20 times higher Young modulus compared with the animal brain.

The schema of 3D printing processes is shown in Figure 2. The Digital Imaging and Communications in Medicine data merge and segmentation was performed mainly by semiautomatic thresholding process and manual operation to identify each anatomic structure and smoothening the model's surface. After a molding material was assigned for each anatomic structure in the printing software, the data were transferred to a 3D printer, and the model was printed in a single printing process for about 8 hours. Excavation was performed for the models of brain, venous sinuses, and tumors for softness simulation. The recommended print conditions for each anatomic structure are shown in Table 1.

FIGURE 2.

The schema of the 3D printing process. A merge process of Digital Imaging and Communications in Medicine data by the prescribed software was followed by a segmentation process. After the molding material for each structure was selected in a 3D printing software, the 3D printed model was created. A hollowing-out procedure was performed on several structures, such as brain, venous sinuses, and tumors. 3D, 3-dimensional.

TABLE 1.

The Printing Conditions for Each Anatomic Structure

Group	Priority	Structure	Molding material	Hollowing out	Practicable procedures
1	Stiffness	Cerebrum	ExS-10A, ExS-15A, S-30A	+	Retract, cut
		Cerebellum	ExS-10A, ExS-15A, S-30A	+	Retract, cut
		Skull	PP-like	-	Drill
2	Vividness	Nerve	S-85A, S-95A	-	Retract, expose
	Intrabony structure	S-95A	-	Drill, expose
3	Combined	Dura matter	S-60A, S-85A (highlight area)	-	Stitch, retract, cut, peel
		Artery	S-60A, S-70A, S-85A	-	Retract, cut
		Venous sinus	S-50A, S-60A	+	Retract, cut
		Tumor	S-40A, S-50A, S-60A, S-70A, S-85A	+	Retract, cut, peel
		Brainstem	S-40A, S-50A, S-60A	+	Retract

Bold letters: The most recommended materials.

Benefits of Stiffness/Vividness Modified Model

To confirm the benefit of the stiffness/vividness modified model, a 3D printed model of a patient with right cerebellopontine epidermoid cyst (Figure 3A) was created. Although the exact stiffness on the hollow brain model could not be measured because of sensor's limitations, it provided realistic sensation to the surgeon, particularly with retraction (Figure 3B), bridging the Young modulus gap between printing material and brain tissue. A bone model was made by PP-like molding material by mixing low levels of Agilus-Clear and high levels of Vero Pure White. High vivid structures molded by mixing of low levels of Agilus-Clear and high levels of Vero Vivid family were clearly distinguishable from other pale structures with deep location (Figure 3C-3H). Especially, intraosseous structures (semicircular canals, the fallopian canal, grater superficial petrosal nerve, and internal auditory canal [IAC]) dura can require high vividness because they have to be exposed by bone drilling (Figure 3C-3E). For the anterior transpetrosal approach, the models of dura and tentorium allowed the practice of multiple techniques, similar to real surgery: peeling (Figure 3D), retracting (Figure 3E), and cutting (Figure 3F). The models of superior petrosal sinus, sigmoid sinus, and tumor also allowed the same technique (Figure 3C-3G) by use of conventional neurosurgical instruments and materials. Stitching incised dura at the Trautmann triangle was possible during a presigmoidal approach (Figure 3H) (Video 1).

FIGURE 3.

Simulation of combined transpetrosal approach in a patient with right cerebellopontine epidermoid cyst. A, A heavy T2-weighted MRI image at a tumor-visible level. B-H, The views of dissection on the 3-dimensional printed model. B, A view of a temporal lobe retraction. C, A view of the mastoidectomy using a high-speed drill with a diamond burr. D, A view after the mastoidectomy with peeling off the dura from bone from the temporal base. E, A view through the ATPA after drilling off the bone of the Kawase triangle. F, A view through the ATPA with cutting SPS off. G, A view through the ATPA for tumor resection. H, A view through the presigmoidal approach with holding dural stitches in the Trautmann triangle (red arrow). a, tentorium; b, posterior cerebral artery; c, temporal lobe; d, fallopian canal; e, semicircular canal; f, SPS; g, sigmoid sinus; h, trigeminal nerve; i, grater superficial petrosal nerve; j, dura of middle fossa; k, inner dura of internal auditory canal; l, dura of posterior fossa; m, tumor; n, flocculus; o, cerebellar hemisphere. ATPA, anterior transpetrosal approach; SPS, superior petrosal sinus;

VIDEO 1. Stiffness/vividness modified 3D printed model applied to the simulation and training of surgical procedures. The model of Case 5 allows the practice of multiple techniques, such as drilling, retracting, peeling, cutting, stitching, and debulking, in the combined transpetrosal approach. All the steps can be performed as usual surgeries by use of conventional neurosurgical instruments. Anatomical structures are identifiable around the brainstem and simulation of how to remove the tumor can be done, while preserving them.

Surgical Simulation with 3D Printed Model

3D printed models were applied for the simulation of SBS procedures in our hospital (case summary and processing conditions for 3D printing shown in Table 2). For these simulations were discussed approaches, patients' positioning, area of craniotomy/craniectomy, corridor for reaching the lesion, and understanding of relationship between lesion and its surroundings. In a foramen magnum meningioma simulation (case 1: Figure 4A), 2 approaches, the far lateral approach and the transcondylar approach (Figure 4B), were compared. Although tumor attachment to the dura was better visualized through the transcondylar approach, there was little difference in its detachment between approaches (Figure 4C). Based on this simulation, the operation had been successfully performed by far lateral approach with similar simulation and intraoperative views (Figure 4D). Case 2 was a patient with recurrent cavernoma located in the midbrain (Figure 4E). The supracerebellar transtentorial approach and the posterior transpetrosal approach (PTPA) were compared. The distance from the dura to lesion was 50 mm in the supracerebellar transtentorial approach and 30 mm in the PTPA. A tentorial incision under PTPA (Figure 4F) provided a favorable corridor for cavernoma removal (Figure 4G and 4H), and the cranial edge of the cavernoma could be accessed and dissected (Video 2). Case 4 was a patient with partially thrombosed giant aneurysm located on the lateral medullary segment of the posterior inferior cerebellar artery (PICA) (Figure 4I). The surgical strategy was discussed first without a cerebellum in place (Figure 4J) to expose the aneurysm and its surroundings and with a cerebellum (Figure 4K) to simulate the placement of a PICA-occipital artery bypass, ligation point of PICA, and the incision area of the aneurysmal wall. All the simulated procedures were successfully reproduced at surgery (Figure 4L).

TABLE 2.

The Case Summary and Conditions of 3D Printing

Case no.	1	2	3	4	5	6	7
Disease	Meningioma	Cavernoma	Aneurysm	Thrombosed aneurysm	Epidermoid cyst	Hemifacial spasm	Meningioma
Location	Foramen magnum	Midbrain	ICA anterior wall	PICA	Cerebellopontine	VA, AICA	Petroclival
Age/sex	55/female	58/male	48/female	50/male	50/male	48/female	55/female
Main discussed point	Approach (FLA vs TCA)	Approach (PTPA vs SCTA)	Applying angle of clip	Area of PICA ligation and aneurysm incision	Approach (ATPA vs combined TPA)	Transposition direction	Approach (ATPA + RS vs combined TPA)
Materialsa/print conditions
Brain	S-40A (H)	ExS-10A (H)	ExS-10A (H)	ExS-10A (H)	ExS-10A (H)	ExS-10A (H)	ExS-10A (H)
Brainstem	S-60A	S-60A	NA	S-60A	S-60A	S-60A (H)	S-60A (H)
Dura	S-60A	S-60A	S-60A	NA	S-60A, IAC: S-85A	S-60A	S-60A, IAC: S-85A
Nerve	Ⅹ, Ⅺ, Ⅻ: S-85A	Ⅲ: S-95A Ⅴ: S-85A	Ⅱ, Ⅲ: S-85A	Ⅶ, Ⅹ, Ⅺ: S-85A	Ⅴ: S-85A Ⅶ, Ⅹ, Ⅺ: S-95A	Ⅶ, Ⅷ: S-85A Ⅸ, Ⅹ: S-95A	Ⅴ: S-85A Ⅲ, Ⅶ, Ⅹ, GSP: S-95A
Artery	PICA: S-70A VA: S-85A	ICA, BA, SCA: S-85A	ICA, MCA, Pcom: S-70A	BA, VA, PICA: S-85A	ICA, PCA, BA, VA, AICA, PICA: S-85A	VA, BA: S-85A (H) AICA: S-70A	ICA, BA, VA, SCA, AICA: S-85A
Venous sinus	SS, IPS: S-60A	TS, SS: S-50A (H) SPS, IPS: S-50A	NA	S-50A	TS, SS: S-50A (H) SPS, IPS: S-60A	S-50A (H)	TS, SS: S-60A (H) SPS, IPS: S-60A
Vein	NA	NA	NA	S-50A	S-60A	NA	S-60A
Bone	PP-like	Skull: PP-like SCC, CC, FC: S-95A	Skull: PP-like Optic strut: S-95A	PP-like	Skull: PP-like SCC, CC, FC: S-95A	PP-like	Skull: PP-like SCC, CC: S-95A
Lesion	S-85A (H)	S-60A (H)	NA	S-50A	S-40A (H)	NA	S-60A (H)

Ⅲ, oculomotor nerve; Ⅴ, trigeminal nerve; Ⅶ, facial nerve; Ⅷ, vestibulocochlear nerve; Ⅹ, vagus nerve; Ⅺ, accessory nerve; Ⅻ, hypoglossal nerve; AICA, anterior inferior cerebellar artery; BA, basilar artery; CC, cochlea; FC, fallopian canal; (H), hollow model; ICA, internal carotid artery; PCA, posterior cerebral artery; PICA, posterior inferior cerebellar artery; SCA, superior cerebellar artery; SCTA, supracerebellar transtentorial approach; TPA, transpetrosal approach; TS, transverse sinus; VA, vertebral artery.

^aMaterial names are cited from identification defined in the Supplemental Table (http://links.lww.com/ONS/A858).

Italic letters: Anatomic structures.

FIGURE 4.

Simulations using 3-dimensional printed models of skull base surgery cases and reviews in their surgeries. A-D, Case 1. E-H, Case 2. I-L Case 4. A, Gadolinium-enhanced-MRI slice of case 1 at a tumor-visible level. B, Two types of models for the simulations of FLA (left) and TCA (right). C, A view simulating FLA with dural incision from cerebellar convexity area to atlas bone level. D, An operative view of FLA with dural incision in the same way as in the simulation. E, T2-wighted MRI image of case 2 at a lesion-visible level. F, A view from above of a temporal lobe-removed model showing a simulation of a tentorial incision by a dissector (*). G, A view of a simulation of PTPA with cutting the tentorium and reaching to the lesion. H, An operative view of PTPA with tentorial incision (yellow dotted lines) in the same way as in the simulation. I, hT2-wighted MRI image of case 4 at the lesion-visible level. J, A postero-lateral view of the aneurysm and its surroundings in the cerebellum-removed model. K, A view during simulation of TCA with planning the area of incision on the aneurysmal wall (red dotted line) and ligation point of PICA (#). L, An operative view under TCA with incision on the aneurysm in the same way as in the simulation. a, posterior condylar emissary vein; b, sigmoid sinus; c, hypoglossal canal; d, medulla oblongata; e, dura of foramen magnum; f, tumor; g, PICA; h, accessory nerve; i, midbrain; j, dura of middle fossa; k, cavernoma; l, superior petrosal sinus; m, tentorium; n, semicircular canal; o, aneurysm; p, vagus nerve; q, cerebellar tonsil; r, hypoglossal nerve. FLA, far lateral approach; TCA, transcondylar approach; PICA, posterior inferior cerebellar artery; PTPA, posterior transpetrosal approach.

VIDEO 2. Simulation video using 3D printed model of Case 2 intending to decide the surgical approach. Comparison between real surgery and simulated surgery are demonstrated. Mastoidectomy, dural incision of middle fossa and posterior fossa, and tentorial incision provide a favorable corridor for cavernoma removal. After the exposing of the surface of the cavernoma, the lesion is partially debulked. The cranial edge of the cavernoma can be accessed, and the complete dissection from the brainstem is performed.

DISCUSSION

A 3D printed model for advanced simulation requires practical application of essential techniques in SBS: drilling, peeling, retracting, and cutting of structures. Matching the stiffness between an organ and its model is one of the most important tasks for producing realistic and practically useful models. In this study, we evaluated the stiffness of animal organs and printing materials, establishing the Young modulus to better reflect materials' mechanical properties. After its measurement, the softest molding material available currently exhibited 20 times higher values than animal brain. Some authors reported a softer brain model with a stiffness on the order of 10 kPa²⁰ or with a shore 00 hardness of 3.3,¹² achieved by the molding-casting process, but investing significantly bigger labor and time.

Based on the physical nature of the Young modulus (an inverse proportion to the amount of strain), a hollow model was supposed to provide the perception of lower modulus values. Practically, the retraction force on a hollow brain model has to be smaller than that of the nonhollow one to obtain the same field of view. Furthermore, the wall with proper thickness in the hollow model could give the durability of the model and the soft sensation with retraction resembling real life; the wall 3 to 5 mm thick seemed to be appropriate from our experience.

The technique for making a hollow structure in a 3D printed model had been reported already in the creation of cerebral aneurysm models.¹³ In this report, a mold of dissolving acrylonitrile-butadiene-styrene resin was used to create the cavity. In another report, an STL data rewritten as a hollow structure with a uniform wall thickness had been used for a model in which the hollow part had been filled with a removable support material.¹⁴ In that method, a small incision had to be performed on the wall of the modeled structure without affecting realistic perceptions, to excavate the located inside support material. We adopted this method for the routinely retracted structures: brain, venous sinuses, and tumors.

In this study, we applied another scale of stiffness called Shore-A, which is quantified as a relative value of stiffness. The value on the Shore-A scale was modified by adjusting the ratio of hard to elastic resin for the printing process. Because the vividness of the material is also affected by this adjustment, particularly the amount of hard resin, there is a dilemma for the materials with lower values of Shore-A, as they lose vividness and that deteriorates discrimination of each structure colors, especially at deep location. To resolve the dilemma between stiffness and vividness, we classified anatomic structures into 3 groups giving priority to stiffness or vividness, according to their practical importance for the simulation, as shown in Table 1. The models of brain and bone were produced with priority to stiffness, because they will be submitted to retraction and drilling, respectively. Structures surrounded by bones were given the priority to vividness, such as semicircular canals, the facial nerve in the fallopian canal, grater superficial petrosal nerve, and inner dura of the IAC, for better visualization during drilling. Nerve structures needed vividness for clearly distinguishable anatomic course at deep locations. Dura matter, arteries, venous sinuses, tumors, and brainstem were classified into a combined group because they were not only exposed at deep locations but also peeled, retracted, incised, and so on.

Besides the close simulation of retraction, another “close to reality” point of the stiffness/vividness modified 3D printed model was the presence of dura matter and tentorium. All this was helpful to reproduce the precise visual aspect and maneuverability in the operating field. This model allowed dural peeling, retracting, cutting, stitching, and tenting during simulations. That had high practical and training value as surgical simulation, particularly for dissection of dura from bone, exposing IAC inner dura by drilling-off petrous bone, and tentorial incisions for reaching a lesion.

From other 3D virtual reality technology simulation tools, Shono et al³ reported a virtual clipping simulator with a graphical user interface equipped with haptic feedback capability, allowing users arachnoid dissection and interactive retraction of deformable brain and other surrounding tissues. However, because the stiffness of each anatomic structure was not considered in this system, haptic sensation is expected to be superior with our 3D printed model. Moreover, there are advantages for using a “real” model: perform procedures using conventional neurosurgical intraoperative tools via the expected corridor and share surgical strategies within the neurosurgical team.

Limitations

The cost for creating 1 model is in the range 350 to 1500 US dollars. The development of low-cost printing materials is desired. The segmentation process requires 5–15 h manual work by a neurosurgeon, which involved the process to adjust the pixels already labeled to properly secure the distance between anatomic structures. We expect that machine learning will reduce this time-consuming process. We will use teacher data to train a computer to learn a program that accomplishes this process. As a result, the amount of time for segmentation will be shortened.

CONCLUSION

We proposed a novel stiffness/vividness modified 3D printed model that allowed simulating multiple procedures in SBS. The hollow structure of the brain model provided a very close perception to the real brain at retraction and was helpful for bridging the gap of Young modulus values between real brain and its model. The visualization and maneuverability in the operating field were precisely simulated on the dura/tentorium-containing model. The vivid structure appearance was very helpful to distinguish structures during their surgical exposure. The practical value of this type of simulation can contribute to more precise presurgical planning and better training in SBS.

Supplementary Material

ons-24-548-s001.csv ^{(815B, csv)}

ons-24-548-s002.csv ^{(754B, csv)}

ons-24-548-s003.docx ^{(23.3KB, docx)}

Funding

This study did not receive any funding or financial support.

Disclosures

The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.

Supplemental Digital Content

Supplemental Table. Physical properties of printing materials. This table explains the characters of printing materials in this study, which are listed in order of the Shore-A scale. By mixing an elastic resin, Agilus-Clear, and vivid hard resins, Vero-Family, 8 molding materials are made and available in the Stratasys J750 printer. The positive correlation between the mixing ratio of vivid hard resins and the Shore-A scale value is indicated schematically. The extremely soft molding materials, Solid Internal Organs Fiber Contraction-1 and Solid Internal Organs Fiber Contraction-4, can be used in J750DAP. The Young modulus of the softer 6 molding materials is also demonstrated.