# Augmented Reality, Mixed Reality, and Hybrid Approach in Healthcare Simulation: A Systematic Review
## 3 Results
### Implementation of the Physical Component of the Simulator (GQ4, FQ6-7)
#### 3.5.1 Materials and Fabrication Techniques (FQ6-7)  
Simulators can consist of commercial or custom-made physical components. The analysis performed to answer question FQ6 (\"Which phantoms are used? (commercial, custom-made)\") reveals that most of the simulators analyzed are custom-made; indeed, a total of 13 studies employ custom-made phantoms, and only five studies employ commercial phantoms. Below, the manufacturing techniques for both of these types of simulators are reported to answer question FQ7 (\"Which simulator manufacturing technique is used?\"). As for the simulators with custom-made anatomical replicas, only three studies [29; 35; 38] do not provide details on the manufactured process, while the others provide a description of the manufacturing method useful to reproduce the simulator. The study in [27] presents a peculiar method for fabricating the anatomical replicas. The phantom includes artificial vertebrae and soft tissue. The synthetic vertebrae are manufactured starting from frozen and formalin-fixed thoracolumbar spines; they are defrosted and dissected, then embedded using a fast curing plastic. In particular, polyurethane foam recipe is used for the inner cancellous core of vertebrae while a resin is used covering a layer of cortical bone. Finally, different mixtures of silicone rubber are used to manufacture the human's erector spinae and the skin, while a thin plastic foil is used to imitate a muscle fascia. In a large part of the studies [22; 23; 24; 26; 28; 29; 31; 34; 44], the authors instead developed phantoms extracting the 3D anatomical models from CT images of real patients. In [22; 23; 24; 26; 29; 31; 34; 44], the virtual anatomical model is turned into a tangible physical replica by using 3D printing technologies and casting fabrication processes. For example, in [34], the authors fabricate a silicone model using a casting technique based on a 3D printed forelimb prototype of a beagle dog. The remaining studies explored the use of 3D printing with the resin and acrylonitrile butadiene styrene (ABS). The resin is used to mimic the skull bone in [22] and to manufacture anatomical structures and surgical tools in [31]. In addition, in [22] the authors improve the model according to a handmade process with a platinum-cure silicone (Dragon Skin; Smooth-On, Inc, Macungie, PA, USA), mixed with some additives in order to mimic human tissue properties such as textures, consistencies, and mechanical resistance. Instead, ABS is employed to 3D print a hip models in [23] because it adequately approximates the mechanical behavior of the bony natural tissue. After that, the hip model is embedded in a soft synthetic foam and covered with a skin-like material which allows an accurate simulation of palpation and incision. In addition, in [24; 26; 44] the ABS material is used to 3D print models for anatomical replicas. In [24], the hybrid simulator includes a physical commercial trunk phantom with replicas of the liver, gallbladder, pancreas, and stomach. The physical environment is enriched with coherent virtual models of the entire abdomen. The replicas are obtained using casting processes of silicone materials and pigment powders. In addition, the stomach and liver are EM sensorized to quantify deformations caused by surgical action. In [26; 44], the hybrid simulator developed by [PERSON] et al. includes both patient-specific models (e.g., liver, gallbladder, pancreas, abdominal aorta, esophagus-stomach-duodenum) and non-patient-specific synthetic organs designed in a CAD environment (e.g., arterial tree, biliary tree, and connective tissue). The strategy used to manufacture patient-specific replicas is the same as that used in [24]. The manufacturing process of the arterial tree and biliary tree involves the use of nitinol tubes joined together by tin wires and covered by a thin silicone layer. In addition, EM sensors are inserted inside the nitinol tubes to implement an AR solution allowing the real-time visualization of the Calot's triangle.