This Instructable illustrates how to create a custom 3D printable prosthetic device using data from a CT scanner. In this case, I will illustrate the process for creating a custom trachea stent. This Instructable does not include information relating to the use of CT scanner or a 3D printer.
First, here are some general definitions that are helpful to know for a better understanding of this specific process.
- Trachea: Simply put, the windpipe. It connects the pharynx and lungs.
- Stent: A "tube" used to treat constricted airways, arteries etc...
- CT Scan: An X-ray that produces cross-sectional-images ("cuts") which may be recomposed into a 3D model.
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Step 1: Stent Design Evolution
First, a brief background on trachea stent design. Current stents (far left stent) are pure extrusions which do not take into account the actual shape of an individuals trachea. The extrusions are often too tight in one area and too loose in another. By using data from a CT scanner a more accurate representation of a trachea may be achieved. The middle and far right stents are produced using a 3D printer.
Step 2: CT Scan
A 3D model of a trachea is generated from a CT scanner. The model is a water-tight (aka 3D printable) mesh file.
Step 3: Isolating Inner Surface
Import the .stl model from the CT scanner into a 3D modeling program such as Rhino. Make sure to be consistent with your units--if the .stl file is in millimeters, the units of your Rhino model should also be in millimeters. Isolate the inner airway using section cuts.
Step 4: Scripting a Mesh
After the inner surface of the airway is isolated, we can map a grid onto it. Using a parametric plug-in like Grasshopper in combination with Rhino makes it easy to test different grid densities and patterns. Most commonly, stents use a diagrid pattern, but other patterns are also worth exploring. A double-helix, coil or a voronoi are among other forms that may be mapped to the surface. One consideration to make during the process is that the grid pattern is intended to serve as a structural armature which will resist compression while also being flexible and adaptive to movement. Another exciting consideration is that a stent is only a few centimeters tall, but the form is easily translatable/scalable to be hundreds of times larger like a building facade.
Step 5: Render
The above renders illustrate the stent fitting perfectly inside of the airway.
Step 6: Print
The model is saved and sent to a 3D printer. As a disclaimer, note that this process is in an early experimental phase, but is proving to offer promise in the future.
Step 7: Casting
Alternatively, the 3D prints may be used to create molds for casting.