JUNE 2022 | The Surgical Technologist | 261 their widespread use in hospitals; stereolithographic models can facilitate preoperative planning at least in complex cases. Their limitations are related to the properties of the materials, which do not accurately mimic those of tissues, and their inability to simulate events such as bleeding and other intraoperative complications that surgeons may encounter [132, 133]. However, its great limitation is the manufacturing time, which usually takes 48 hours to have a final model, which significantly delays the corrective power in emergency situations [134]. Some centers already use this technology for the generation of specific models adapted to the patient and training templates for staff [135]. The accuracy of the quality of 3DP adapted to the vascular anatomy of the patient in current comparative studies shows high-quality predictive results (<1 mm difference of the printed vessel wall whether aortic or coronary compared to that predicted in digital imaging and communication in medicine (DICOM) studies), this for FDM and Polyjet technologies [136]. 3.3. Digestive System 3.3.1. Gastrointestinal. Over time, novel technologies and the introduction of diagnostic imaging have reshaped the practice of surgery. In this context, it allows the creation of graspable, patient-specific, anatomical models generated from medical images. The ability to hold and show a physical object facilitates the understanding of complex anatomical details such as seen in invasive gastrointestinal tumors located, for instance, in the pelvic cavity or in situs inversus [16, 138–140]. Patient counselling, as well as medical education, and surgical training, will definitely benefit from AM. Pietrabissa et al. found that the most common application of 3DP in gastrointestinal surgery was surgical planning, education, training and anatomical comprehension of the disease [141]. One of the more challenging procedures in gastrointestinal surgery is esophagectomies and the subsequent reconstruction. To date, the rate of complications is high despite multiple efforts and different strategies [142, 143]. If esophagectomies are performed, this situation has led to the development of alternative treatment technologies like esophageal transplantation. For instance, Takeoka et al. developed a scaffold-free structure with a mixture of cell types using bio-3DP. His team transplanted the structure into the esophagus of murine models with good functional results. The successful outcome was related to the higher content of human bone marrow-derived mesenchymal stem cells [144, 145]. In a similar study, and using tissue-engineered scaffolds, Park et al. demonstrated that those which had 3DP polycaprolactone (PCL) scaffolds presented better muscle regeneration. Also, better epithelialization was observed with polyurethane- (PU-) nanofiber (Nf) scaffolds [146]. In the case of inoperable esophageal tumors, the major treatment of choice in order to alleviate dysphagia is the use of esophageal stents such as self-expandable metallic stent (SEMS) and self-expandable plastic stent (SEPS), however, there is a current development of novel personalized 3Dprinted esophageal stents with the goal of improving the symptoms and to provide local anticancer therapy (Figure 5) [147]. In the case of complex anatomy, 3DP is useful for the better visualization and planning of complex surgeries. Some potential examples of the advantageous use of AM technology are in the surgical planning of aortoesophageal fistula repairs and laparoscopic resection of multiple esophageal diverticula [148]. Having a 3D anatomical model resembling the anatomy that will be explored in the OR enables to develop strategies for saving time, with optimum postoperative results. In terms of medical education and training, multiple institutions like the University of North Carolina and the University of Toronto have acknowledged the need of 3D-printed organs for a surgical simulation curriculum [149, 150]. Some procedures that started to use 3DP for training are in the treatment of pyloric stenosis [151] and dissection of the complex vascular anatomy of the celiac trunk [152]. A recent paper published by Stier et al. showed a novel use of quantitative three-dimensional computed tomography volumetry (3D-CT) of the upper gastrointestinal tract in bariatric surgery, where they found that it facilitates the identification of the postsurgical three-dimensional gastric anatomy and also can be used as an additional diagnostic tool in postbariatric patients with postprocedural complications or prior to revisional procedures [153]. The use of 3DP in colorectal surgery has also impacted the treatment at many levels. For example, the use of individualized models of stomas in order to educate patients andfind the right fit of ostomy bags in patients with difficult abdominal wall anatomy [154, 155][17, 18]. With regard to preoperative planning and intraoperative guidance for laparoscopic resection of liver metastases due to colorectal cancer, it is evidenced in the review done by Emile and Wexner that 3D models were supportive, especially in those tumors that were not palpable or recognized by intraoperative ultrasonography, as well as described in by Witowski et al., where obtained that the patients presented a decrease in postoperative complications, being considered a costeffective technique [154, 156, 157]. One of the most promising aspects of surgical planning and 3DP is pelvic surgery. Hamabe and Ito developed a 3D model of pelvic muscles and neurovascular structures for total mesorectal excision (TME) and lateral pelvic lymph node dissection (LLND). They demonstrated a better anatomical recognition that facilitates the dissection and resection with optimum postoperative results [158]. Also, another novel 3D-printed device was carried out by Rodriguez-García et al. to perform transanal endoscopic surgery without pneumorectum [159]. Chen et al. demonstrated that the preoperative use of 3D models for the resection of right colon tumors resulted on a decrease in operative time, amount of bleeding and greater resection of lymph nodes in comparison with those cases in which these models were not used [160]. Likewise, Sahnan et al. demonstrated that, when 3DP is used for the repair of anal fistula, the results this technology improve the anatomical assessment and its correlation with imaging during surgery, as well as serving as a medium to enhance the education of 9 BioMed Research International
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