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The PDI Squirt Shape™ 3D Printer
The Squirt ShapeTM machine was originally developed by Josh Rolock in the late 1980’s as a PhD student at Northwestern University. After the project was cut and defunded, Prosthetic Design, Inc. (PDI) privately funded and further developed the machine. In 2009, PDI’s sister company, Dayton Artificial Limb Clinic (DALC), began selectively fitting patients with PDI Printed Sockets. After observing a better fitting device and satisfied patients, DALC converted all patients to PDI Printed Sockets in 2013.
The PDI Squirt ShapeTM 3D Printer is unlike any other additive manufacturing device. Our device is capable of 3D printing structurally sound prosthetic sockets due to it’s continuous, spiral printing technique, which allows the final product to be extremely strong and durable. The PDI Printer can extrude 28 times more material per minute than your typical 3D printer. As a result, the average print-time for a transtibial socket is approximately 1 ½ hours, and 2 ½ hours for a transfemoral socket.
The most shocking aspect of the socket itself is its ridges. The cylindrical printing method we utilize leaves a ridge for each layer, which can be minimized by modifying extruder parameters. However, we have found through clinical application that our textured sockets allow our patients to experience a better fit by providing more surface area for the liner to interface with, thus more friction and less movement of the patient’s limb.
Commonly Asked Questions
Dayton Artificial Limb started fitting patients in 2009 and have seen no failures to date. The proprietary material used by the PDI Printer and the amount of material the machine can extrude allows for a high-strength device.
Vice Clamp Demonstration
The printed socket is textured due to ridges at each layer. Socket texture can be alarming when observing for the first time, especially when we have been taught and trained that everything should be smooth. Clinically, we have seen this to improve the fit of the socket. Each groove increases the surface area at the liner-socket interface, thus increasing static friction which reduces movement within the socket. PDI is currently collaborating with Northwestern University on research project funded by the Department of Defense to obtain data on textured sockets (see link for details: http://www.nupoc.northwestern.edu/research/projects/lowerlimb/nolongersmooth.html#nolongersmooth).
Amputees wear a liner that is anywhere from 3-9mm thick and cannot feel the texture, nor is anything present that can damage their skin.
PDI Printed Sockets
Clinically, we have not seen any liner breakdown due to the texture. Dayton Artificial Limb Clinic, Inc. has been fitting 100% of their patients with PDI Printed Sockets since 2013. From our experience, we have concluded liners do not see additional wear due to texture because less movement within the socket. Less movement due to texture minimizes shearing and wear.
PDI Printed Socket System
PDI currently fabricates off-the-shelf and custom liners. As you can see in the figure below, these mate up perfectly because the liner is made with 3D printed molds and have inherent texture from the print. DALC fits 85% of my patients with this type of liner. Other types of liners from Otto Bock and Ossur, for example have also coupled well with the socket according to clinical experience by ourselves and central fab customers.
Bisected PDI Printed Socket System
The PDI Printer’s setting can be adjusted to obtain different texture configurations (as shown below). Contrastingly, the ridges can also be minimized by altering the machine’s settings, but this extends the print-time and does not cause the socket to be completely smooth.
Example Socket Texture Configurations
You can smooth out the lines with a torch after the socket is printed (see example below). We do have to do this with my AK amputees that have an internal seal like Ossur’s Seal-In liners. The print process is a constant spiral from the distal to proximal end, thus a channel for air to leak. We heat a 50mm region at the seal height of our BK sockets as well to produce a more sufficient seal.
Clinically, it has been determined approximately 2mm texture is the maximum amount that should be implemented for BK sockets. This is due to prominent boney structures. The maximum allowed texture for AK sockets has not been determined. The printer program currently maxes out at around 8mm depth, which is sufficient when fitting patients. Below you will see one of our AK sockets that this patient has been wearing for the past 2 years. This specialized texture helps control soft tissue by increasing surface area.
Texture Configuration for Controlling Soft Tissue