3D Printed Adult Male Humeral Bone Models/Check Print Settings

Filament Material: PLA AT ALL ORIGINAL DEFAULT SETTINGS

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• To ensure tactile fidelity of the Humeral Shaft Transverse Fracture Simulator and avoid mechanical failure of the bone models, the bone models must be 3D printed using polylactic acid (PLA) filament because PLA has a hardness value (Shore Hardness 80D-88D) that is very similar to human cortical bone (Shore Hardness 79D to 93D).^{[1][2][3][4][5]}
• Do not substitute PLA filament with acrylonitrile butadiene styrene (ABS), engineering co-polyester (CPE+), or glycol-modified polyethylene terephthalate (PETG) filament because our December 26, 2021 internal testing found that 3D printed bone models made of Ultimaker ABS filament (Shore Hardness 76D), and Ultimaker CPE+ (Shore Hardness 77D) were unable to tolerate powered or manual drilling of a self-drilling 4.5 mm diameter Schanz Screw during simulation training, and our research has found that Ultimaker PETG has a Shore Hardness of 76D.^{[6][7][8][9][10]}
• To prevent print quality issues, if you have previously modified any values from the 3D slicer program's default settings for PLA filament, please change these values back to the default settings by clicking on the circular arrow to the left of each modified setting.

Support: NONE

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• Do not select the "Support" option because support material will cover up the semi-engraved features on the base of each model designed to assist with model identification and proper orientation.

Layer Height: 0.15 - 0.3 mm OR LESS

Wall Thickness: 5.5 mm (THIS CHANGES THE WALL LINE COUNT)

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• To avoid print quality issues, the layer height should be 0.15 mm to 0.3 mm or less.
• The wall thickness value is set to the average far cortex thickness for the distal end of the humeral shaft for male adults ages 21-45.^[11]

Top Layers: 0

Bottom Layers: DEFAULT VALUE (NOT 0)

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• The Top Layers should be "0" to allow the humeral bone's interior anatomy (outer cortex and inner cancellous bone) to be exposed at each fracture end to provide visual fidelity for the Humeral Shaft Transverse Fracture Simulator.
• Do not change the Bottom Layers to "0" because this will make the base open at the bottom which negatively impacts the aesthetics of the simulator.

Infill Density: 15%

Infill Pattern: TRI-HEXAGON

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• The infill density is set to simulate human cancellous bone porosity.^[12]
• The infill pattern is selected to simulate human cancellous bone microstructure.^[13]

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• Our internal testing on October 22, 2022 showed that reducing the Top/Bottom Speed to 20.0 mm/s allows adhesion of the base of the model to the build plate on a Creality Ender 3, Prusa i3MK3S, and Ultimaker 2+ Extended 3D printers. We opted to recommend a Top/Bottom Speed of 15.0 mm/s to add an additional safety margin to cover the range of 3D printers on the market.

Build Plate Adhesion Type: NO RAFT

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• Do not select the "Raft" option because a raft will cover up the semi-engraved features on the base of each model designed to assist with model identification and proper orientation.
• The skirt is usually the default setting for 3D printers and is preferred because it permits removal of the 3D printed model with no post-processing. Our internal testing found that our models can be printed with a skirt (and no brim) on Prusa i3MK3S 3D printers using a PEI build plate.
• However, 3D printers with build plates made of glass will likely require a brim to ensure adhesion of the 3D printed object. Please follow the build plate manufacturer's recommendations for using a brim to ensure adhesion of PLA to the build plate.^[14]
• 3D printers without heated build plates will likely require a thin layer of glue and potentially a brim to ensure adhesion of the 3D printed object. Please follow the build plate manufacturer's recommendations for using glue and adding a brim to ensure adhesion of PLA to the build plate.^[14]

Filament: WHITE PLA JUST FRESH OUT OF SEALED PACKAGING

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• To ensure visual and tactile fidelity of the Humeral Shaft Transverse Fracture Simulator, the bone models should be 3D printed out of white polylactic acid (PLA) filament because because PLA has a hardness value (Shore Hardness 80D-88D) that is very similar to human cortical bone (Shore Hardness 79D to 93D).^{[1][2][3][4][5]}
• Using fresh PLA filament just out of its original packaging optimizes print quality and minimizes the risk of mechanical failure during orthopedic surgical simulation training.^[15]

Print Speed on 3D Printer Control Screen: 100% or less

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• If the print speed is too high, it will cause loss of adhesion to the build plate leading to print failure or it can result in filament drooping on the vise attachment, which adversely impacts print quality.