An ankle-foot orthosis (AFO) is an L-shaped orthotic device supporting the lower leg and foot. AFOs are used to remedy abnormal gait patterns, control ankle movement, and compensate for muscle weakness in patients experiencing drop foot. They are also used to treat patients with arthritis, adult acquired flatfoot deformity, and fractures.
A junior biomedical engineering student was tasked to develop a custom fit AFO, after she had independently gained 3D scanning and modeling experience. The following outlines the development process and pedagogical conclusions from the experience.
• 3D Scanning:
o Utilizing a FARO Arm laser scanner, a point cloud replica of the lower leg and foot anatomy was generated. Multiple scans were manually registered and merged to create a single model, then globally registered to fine tune the anatomical data.
• 3D Data Manipulation:
o Geomagic Studio software was used to reduce noise and outlying points while retaining the scanned detail. The Points Wrap command helped reduce the points and generate a uniform .wrap file.
o The Polygon Phase capabilities of Geomagic Studio were used to repair intersections, fill holes, and refine floating data and edges. The Select by Curvature command was employed to relax the structure while retaining detail. A NURBS (Non-Uniform Rational B-Spline) surface was created to finalize the mesh structure and export it as an .stl file.
o Once a 3D mesh is generated, the number of triangles comprising the mesh must be reduced in order to lower computing lag. MeshLab software was utilized to reduce the number of triangles below 8,000.
o Autodesk Meshmixer allows for simple, yet detailed modification of .stl files through direct editing of a mesh geometry, a feature that is not available in SolidWorks. SolidWorks requires a subtraction command to generate the scanned structure onto a part. With Meshmixer, the AFO is produced directly from the patient’s original scan without losing much detail or accuracy. After the .stl was imported, the Extrude command was used to produce depth for the 3D Printing Process. Next, the data was modified by removing excess material and utilizing smoothing and sculpting commands to produce a clean and detailed structure.
• 3D Printing:
o The final .stl file was printed in scale for form checking in a UPrint SE machine.
This lean process results in a custom-fitted AFO matching the patient’s lower limb anatomy. The use of safe laser scanning technology produces data that will remain available for future reprints of the custom device in case of wear or lost equipment.
The student was presented a set of Geomagic Tutorials and supplementing data after a FARO Arm demonstration. No further instructions were given. The student faced a large time commitment over several months but acquired strong knowledge and great amount of skills in 3D Scanning, Data Manipulation, and 3D Printing, along with AFO design knowledge. The student’s competency and confidence also improved. After completing this project, she took an internship position with a high-tech tissue simulation/phantom company and performed successfully with the skill and knowledge gained from this project.
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