Development of the model was through collaborative efforts of a team involving engineers, designers, and clinicians. The initial design was based on an existing ribcage model . This model was separated into five elements using Autodesk® Meshmixer (Version 3.5, Autodesk, Inc 2020) which were printed individually due to printer size constraints. The model was then assembled from the component parts.
The bone portion of the thorax included the ribcage, a sternum, two clavicles, and flexible spine. The ribs, sternum and clavicles were printed as separate pieces using ivory-colored polylactic acid (PLA) and soluble polyvinyl alcohol (PVA) support. At areas in which no flexibility was required, such as between the sternum and collar bones, separate parts were bonded together using glue. The printer used for these sections was the Ultimaker© 3 3D Printer.
In areas requiring flexibility, such as between the ribs and sternum, flexible joints were created as single units using thermoplastic elastomer (TPE) 90A as well as PVA. Ribs requiring flexibility were fixed to the sternum and spine using these. The printer used for these joints was the Airwolf© Axiom Dual Direct Drive 3D Printer.
The skin for the thorax was created as a large overlaying portion with a small cut-out replaceable skin section. This allowed repeated use of the model while minimizing waste and associated cost as the large skin overlay was not manipulated during practice. The outer skin had three layers: the top skin layer was made of SmoothOn Ecoflex 00-30, the middle SmoothOn’s expanding silicone foam SomaFoma15, and the innermost layer SmoothOn Dragon Skin 10. The skin was made by pouring each successive layer onto a flat surface and then cutting to an appropriate size. The smaller, replaceable skin pieces had an identical composition. Figure 1 shows the completed model design with and without the overlaying skin piece.
This early prototype integrated an anatomically realistic 3D-printed heart and functional “lungs”, created using plastic tubing as the “trachea” and two punching balloons for the lungs, inflatable using a bag valve mask setup. These additional materials cost approximately $10 and will be refined on future models. The entire model sits on a stand that was designed using Autodesk Fusion 360 on the Ultimaker© 3 3D Printer using PLA.
The total cost of the model design was approximately $180 CAD. A summary of the equipment, supplies and cost breakdown for each part is included in table form as part of the Online Supplement.