Brad Poziembo thinks that the prosthetic field needs to embrace the existence of 3D printing and the improved care that it can provide. Most practitioners are still using techniques from the 1950s even though several computer aided methods are available. After he inherited a twenty year old research project involving an injection molding 3d printer called Squirt Shape, originally started with Joshua Rolock at Northwestern University through a VA grant, he decided to move the industry forward on his own.
The Squirt Shape is unusual for several reasons but the greatest is the way that plastic is delivered to the build area. A polypropylene collar is fastened to a rotating plate and plastic pellets are delivered from a hopper to an extruder like an injection mold process. The build plate spins and the controller tells the extruder how far to move from the axis to create the required geometry for the component.
Images courtesy of Prosthetic Design, Inc.
A blend of polypropylene pellets are used to create the proprietary material and the machine can extrude layers up to ½ inch (12mm) wide and 1/8 inch (3mm) in height. Mach3 CNC software and MATLAB work together to control the speed, distance from center, temperature and bead height. Scans from the patient’s residual limb act as the input data and a fully complete socket is the eventual output.
A full socket for a leg uses about ¾ cup of raw plastic pellets, takes between one and two hours to print and can be up to 14 inches in diameter and 26 inches tall. The linear layers of plastic cause heavy grooves in the surface of the socket, allowing for better friction to the silicone interface that fits over the patient’s residual limb. As a result, a superior fit is achieved.
Seeing this machine in action was amazing and it’s unlike any other 3D printers that I’ve encountered in person or online. Current cycle times are around a tenth of what we can do with current x-y-z 3D printing technology, and Poziembo still wants to squeeze as much out of the cycle time as possible. A Kickstarter funding campaign is planned for late 2015.
Images courtesy of Prosthetic Design, Inc.