Northwestern University Feinberg School of Medicine

Northwestern University Prosthetics-Orthotics Center

Rapid Prototyping Lab

NUPOC Rapid Prototyping Lab

The Computer-Aided Design and Manufacturing (CAD/CAM) Laboratory is where the original research and development on Squirt Shape, an additive fabrication technology for the production of prostheses and orthoses, took place. A Partner I computer-numerically controlled (CNC) milling machine with four axes of simultaneously controlled motion (the four axes are the x, y, z, and a rotary axis) served as the backbone of the alpha-prototype Squirt Shape system. We also developed a beta-prototype of Squirt Shape that uses a water-cooling method to speed-up socket construction.

The CAD/CAM Lab is equipped with a Stratasys Fusion Deposition Modeler (FDM) 400mcTM.  This rapid prototyping machine uses data in the form of stereo lithography (STL) files that computers can use to make 3-dimensional objects such as prosthetic sockets.  Fabrication is totally automatic and is accomplished by using a dispensing nozzle to deposit thin layers of liquefied plastic which quickly hardens into a solid. This equipment allows researchers to rapidly fabricate prototypes, thus enabling early error correction and prediction of end product performance.

The CAD/CAM Lab is also equipped with a Provel d1 mechanical digitizer and Shapemaker software. The mechanical digitizer measures the dimensions of a cast or mold of the residual limb and transfers the data to the Shapemaker software, which creates a three-dimensional computer model. This computer model of the residual limb is modified digitally to relieve pressure in sensitive areas and apply pressure in tolerant areas. Once modification is finished, a data file with positional instructions can be sent to systems like Squirt Shape and Stratasys for fabrication.

The CAD/CAM Lab also is equipped with an Inspeck 3D Megacapturor, which can digitize complex shapes such as hands, arms, legs, feet, torsos or heads.  This optical system projects a sinusoidal pattern onto the surface of an object that is captured by a single camera as 300,000 to 7,800,000 sampled points.  Both geometric and texture data are captured. The stripes appear distorted and an analysis of the distorted patterns is used to calculate the 3-D surface shape.  This digitizer provides a photographic record as well as a computer image that helps researchers visualize and measure three dimensional shapes.

These CAD/CAM resources are utilized in many of our projects, including those focused on socket development and gait studies of amputees where multiple prostheses per subject are needed. CAD/CAM enables easy iterative modifications to socket shape and rapid fabrication of prosthetic sockets. Such procedures would be very time and labor consuming if performed manually.

Rapid Prototyping Lab at NUPOC

Prosthetic socket prototypes created in the Rapid Prototyping lab at NUPOC.