Three-Dimensional Printed Gastrointestinal Tract Models for Surgical Planning and Medical Education: A Systematic Review

1. Introduction

Owing to rapid technological advancements, three-dimensional (3D)-printed models have been extensively employed in surgical planning and medical education. 3D-printed models enable direct visualization of anatomical structures and provide a tactile experience for practice [1,2].

In surgical planning, 3D patient-specific printing technology can help surgeons understand complex anatomical relationships and determine which structures can be safely altered or removed. Compared with conventional two-dimensional imaging, a 3D-printed model can provide more complex information for surgical planning in a shorter timeframe [3].

3D-printed models have been utilized for preoperative assessment and surgical training in various conditions, including coronary artery disease, congenital heart disease, kidney and liver diseases, and hepatobiliary diseases [4,5,6,7,8]. These studies have demonstrated the clinical value of using patient-specific 3D-printed models in guiding surgical planning, particularly for complex or challenging conditions.

For the gastrointestinal tract, simulation-based training is becoming an inherent part of medical training. Simulation can improve trainees’ professional skills in a risk-free environment, especially for surgical procedures. The existing simulators are physical/mechanical simulators, animal models (both in vivo and ex vivo), and computerized simulators. Conventional mechanical simulators provide natural tactile feedback [9,10]. However, this type of simulator lacks realism and complexity in simulating the human structure [11]. Animal models can provide actual haptic feedback, allowing trainees to experience authentic clinical interventions [9]. Nonetheless, these models are expensive and are difficult to collect and maintain. Computerized simulators can provide multiple endoscopic procedures, anatomies, and interventions for training but lack realistic force feedback and are not cost effective [9].

Recently, 3D-printed models have been utilized for gastrointestinal tract applications, including gastroscope biopsy training, gastric hemostasis training, and presurgical evaluation for gastrointestinal cancer [12,13,14,15,16]. Compared with conventional physical models, 3D-printed patient-specific models are durable, inexpensive, easy to produce, and achieve anatomical realism. Therefore, 3D-printed gastrointestinal models can be valuable and have the potential to serve as training models for presurgical planning and education.

This systematic review aims to summarize the current role of 3D-printed models in the gastrointestinal tract and to explore their application for future practice and research. The rationale for conducting this review is to analyze the current literature regarding the usefulness of 3D printing technology in gastrointestinal diseases. As most studies focus on the applications of 3D printing in maxillofacial and cardiovascular diseases, this review is expected to provide an update on the current status of 3D-printed models in the gastrointestinal arena.

2. Materials and Methods

2.1. Search Strategy

The literature search was conducted in accordance with the PRISMA (Preferred Reporting for Systematic Reviews and Meta-Analysis) guidelines [17]. The search databases for this review were PubMed/Medline, Scopus, and Embase (Table 1).

2.2. Inclusion and Exclusion Criteria

The articles were managed using the EndNote (v. 20.6) software. Endnote’s automated processes removed duplicate records.

Reports were included if they were original, full-text, peer-reviewed articles written in English and published in the last 10 years exploring the use of 3D-printed models of the gastrointestinal tract. Articles discussing 3D-printed model production methods/materials were included. The limited original research present in the literature ultimately required the inclusion of case reports.

Articles were excluded if they exclusively discussed using 3D-printed models for medication or animal tests, including articles about 3D-printed gastrointestinal vascular models. 3D-printed models of the digestive glands, such as the liver, gallbladder, and pancreas, were also excluded. Gray literature, including conference papers, letters to the editor, books, practice guidelines, and preprints, was also excluded.

2.3. Article Quality Assessment

The quality of each study was assessed using the “Quality Assessment Tool for Studies with Diverse Designs” (QATSDD) developed by Sirriyeh et al [17].

2.4. Data Extraction and Synthesis

The data for this study were collected on the purpose and applications of 3D-printed gastrointestinal tract models, including the organs printed, sample size, imaging modalities, and software used for 3D printing, as well as the 3D printers, materials used, relevant findings, research limitations, and the country in which the studies were conducted. The data extraction was performed by one observer (JL) and double-checked by another observer (ZS).

3. Results

3.1. Study Selection

Nine duplicates were removed after searching three databases. The remaining articles were screened based on title and abstract, and 288 unrelated articles were removed. Following full-text screening, articles were excluded if they did not involve human gastrointestinal tract models. Eighteen eligible articles were identified via full-text screening [18,19,23,24,25,26,27,30,31,32,33,34,35,38,39,40,41,42]. An additional seven articles were selected from the reference lists [20,21,22,28,29,36,37]. The total number of articles included in the review was 25 (Figure 1).

3.2. Study Characteristics and Findings

Table 2 lists the design characteristics and key findings of these 25 studies. Of these, 16 were experimental studies [18,19,21,22,23,24,25,27,32,33,34,35,36,37,38,39], 4 were case reports [20,26,28,41], and 5 were descriptive surveys [29,30,31,40,42]. Thirteen studies equally represented the USA [18,20,23,38,41], Canada [25,30,34,35], Germany [19,37], Italy [28], and UK [36]. Ten studies were from Korea [21,24,27,29,32,40] and Japan [22,26,31,33]. The remaining two studies were from Slovakia [39] and China [42].

3.3. 3D Printing Details

Table 3 presents the 3D printing details of all 25 studies, including the imaging modalities used for 3D printing, the software used for image processing, the organs printed, the 3D printers employed, the 3D printer materials, the printing time, and the printing cost.

3.3.1. 3D Printing Processing and Materials

Of the 25 studies, 16 used CT imaging for 3D printing [19,20,21,22,24,26,28,29,30,31,32,33,36,39,40,41], 1 used both CT and magnetic resonance imaging [42], and the remaining 8 did not mention the data resource for printing. Eight studies mentioned the printing method. Six used fused deposition modeling (FDM) [24,30,33,39,40,42], and two used stereolithography printing modeling [28,32].

The 3D printing time varied from 6 h to 48 h. The highest printing cost was $1175 [18], and the lowest was $1033.

Silicone was the most commonly used material, accounting for 45% of the studies [18,19,22,24,25,27,29,32,34,35,36,39,40]. The second most commonly used material was polylactic acid (PLA) [23,25,33,35,39]. Other printing materials included resin, rubber-like material, PlatSil Gel-10, and plastic (Figure 2). In Yu et al.’s study, PVA/polyacrylamide (PAM) hydrogels were utilized as a novel material for gastrointestinal 3D printing. Six studies used two materials concertedly to print models [25,27,32,35,39,41].

3.3.2. Printed Gastrointestinal Organs

According to the 25 studies, 3D-printed gastrointestinal organs included the entire digestive tract. With 10 articles (42%), the stomach was the most frequently modeled organ [18,21,24,25,27,28,29,32,38,42] (Figure 3). 3D-printed rectum models were reported in only three studies [19,22,41]. Most studies (67%) used CT images for 3D printing.

3.4. Purposes of 3D-Printed Gastrointestinal Models

Nineteen studies focused on specific training and preoperative assessment for gastrointestinal tract surgery or other procedures [20,21,23,24,25,26,27,28,29,31,33,34,35,36,38,39,40,41], including two pediatric surgical planning [25,36]. Three studies developed abdominal, gastric, and laparoscopic phantoms [19,30,32]. Two studies were designed to create training models for colonoscopy [22,37]. One study utilized a novel material for gastrointestinal 3D printing [42].

3.5. Quality of the Studies

The articles included in this review were heterogeneous and comprised four case reports [20,26,28,41]. All 25 studies were evaluated using “QATSDD” developed by Sirriyeh et al [17]. The quality of the trials varied, ranging from 21.4% to 76.2%. Six studies were rated <50%, four of which were case reports. The results are presented in Table 4.

4. Discussion

Analysis of the 25 studies included in this review revealed several key findings. First, 3D-printed gastrointestinal tract models can enhance technical skills, knowledge, and confidence in performing gastrointestinal surgery or other procedures in a risk-free environment. Second, the 3D patient-specific printing method enables the creation of realistic anatomy, haptics, modularity, and reproducibility for presurgical planning and training. Nonetheless, most were small-sample studies and lacked comparison analysis. The influence of the models on actual patient procedures was not followed up. In addition, most of the 3D-printed models in these studies were designed for a single procedure, which limits their widespread application.

4.1. 3D Printing Methods and Materials for the Gastrointestinal Tract

According to current studies, FDM is the primary method for 3D printing of the gastrointestinal tract. FDM is a popular 3D printing technology with rapid production, cost-efficiency, accessibility, broad material adaptability, and the ability to produce complex components [43,44]. Stereolithography printing has also been utilized for producing 3D models of the gastrointestinal tract, but its cost is higher than that of FDM. Furthermore, research on the technical differences among various 3D printing technologies for the gastrointestinal tract is limited, and data on printing time are scarce. Only four studies have reported printing times ranging from 6 h to 48 h [28,33,39,42]. This lack of details affects the overall assessment of the current gastrointestinal 3D printing technology.

Silicone is the most commonly used printing material for gastrointestinal models that can provide tactile feedback to users. Several types of silicone suitable for 3D printing of the gastrointestinal tract have been investigated. Kenngott et al. compared three types of silicone for 3D printing: Ecoflex 0010, Ecoflex 0030, and Dragon Skin FX-Pro [19]. In this study, 10 silicone rectum models were produced using mixtures of different silicone types. The rectum model created with three parts of Ecoflex 0030 and one part of Slacker showed the best results in terms of haptic realism. In Kwon’s research, the tensile strengths and elongations of three materials were compared according to the number of silicone coatings [32]. Habti’s research produced six silicone 3D-printed models of the small bowel, each with a different Shore hardness. The model with a Shore hardness of 0–30 was considered the most representative of small bowel anastomosis tissue [35].

PLA is often used in combination with silicone. Studies have documented the use of PLA to print molds and then silicone to prepare the final intestinal model [25,35,39]. Resin-printed models have been used in some case reports for presurgical planning [28,41].

Apart from the above-mentioned printing materials, one study explored the application of PVA/PAM hydrogels in 3D-printed models. This research noted that PVA/PAM hydrogels were an elastic and flexible material that closely simulated the physical characteristics of soft tissues, such as the brain, liver, and gastrointestinal tract [42]. This research has provided potential innovative material for future 3D gastrointestinal printing.

There is a dearth of studies comparing various printing materials. Examining more realistic printed materials is a potential research area.

4.2. 3D Printing of Gastrointestinal Organs and Their Applications

The common 3D-printed gastrointestinal organs are the stomach, colon, and esophagus. Most studies have focused on specific training and preoperative evaluation for surgeries and other procedures related to the gastrointestinal tract.

The endoscopic procedure is the primary treatment for gastric diseases. Therefore, 3D-printed stomach models have predominantly been applied for endoscopic procedure training, including endoscopic ampullectomy, biopsy, endoscopic hemostasis, intragastric balloon, and stent placement training [18,21,24,27,29,38].

Unlike the gastric model, the 3D-printed colon model focuses on preoperative planning in addition to endoscopic training, which is associated with a high incidence of colon tumors. 3D-printed models have provided patient-specific anatomy and more accurate identification of tumor locations for surgeons under challenging conditions [26,31]. Moreover, studies have analyzed the colon morphology and designed models based on three common morphological patterns to improve their realism [22].

The use of the 3D esophageal model has increased in recent years. Dickinson et al. reported the first application of 3D-printed esophageal models to complex esophageal cases [20]. The studies of Neville et al. and Zahradniková et al. explored the use of 3D esophageal models in pediatric surgery. The researchers developed 3D-printed esophageal models for esophageal atresia with tracheoesophageal fistula repair [36,39]. Most participants opined that the 3D model was a suitable training tool. The 3D-printed model can potentially be used as a training tool by pediatric surgeons for esophageal procedures.

Participants’ assessment of the 3D-printed models was evaluated using a 5-point Likert scale questionnaire survey tool. These studies showed that 3D-printed models can provide a better appreciation of anatomic relationships, more realistic tactile feedback and visualization, and augment the participants’ confidence and skill in gastrointestinal tract surgery and other procedures.

Current research has also mentioned the disadvantages of 3D-printed gastrointestinal models. Gastrointestinal tract peristalsis and movement cannot be reproduced in 3D-printed models, and the elasticity cannot reach the same level as that of a real organ.

4.3. Limitations

Some limitations need to be acknowledged. First, the results of the studies in this review are based on participants’ subjective evaluation and lack comparison with conventional clinical training and other models. Only two studies compared the 3D-printed model with previous simulators [22,37]. There could be a possible bias in evaluating the simulator using questionnaires²⁴. The impact of this simulator on actual clinical practice outcomes remains unknown [37]. Second, some studies did not provide the details of 3D printing, which makes it difficult to compare the methods.

5. Conclusions

This study has analyzed the development and application of 3D-printed gastrointestinal tract models in presurgical planning and medical education in the last decade. The literature review has established that 3D-printed gastrointestinal models provide realistic anatomical structures and enhance the trainees’ skills and confidence by using real patient images. However, the model’s elasticity must be improved to simulate the real organ. Future research should focus on comparing the models with other simulators and examining their impact on actual gastrointestinal procedures.