I’ve been working the the amazing e-NABLE community for a little over a month now and have never seen anything quite like it. It’s an interesting case study on a number of levels: as an example of emergent web-based communities, of self-organizing systems, and of excellent applications of the capabilities of 3D printing. We’re working to build a peer-to-peer infrastructure to facilitate the fabrication and distribution of 3D printed assistive devices (prosthetics) for individuals with upper limb differences. In addition to fabrication the group is very interested in development and innovation. That is certainly part of what drew me to them. The challenge of highly customized prosthetic devices for rapidly growing children is remarkably well suited to 3D printing.
I decided early on to work on the part of the device that interfaces with the user, the “gauntlet”. In individuals with amniotic band syndrome (ABS), the gauntlet is composed of a hand-piece and and arm-piece, each precisely fitted to the user’s body to function comfortably without abrading/pinching/or otherwise irritating the user’s skin. In the case of the Robohand, one of the first 3D printed prosthetic hands developed by Richard Van As and Ivan Owen, a medical-grade thermoformable plastic sheet (Orhtoplastic) is molded to the user’s arm and hand and the rest of the device is then mounted to these two plastic pieces. I did a few quick experiments with thin sheets of PLA in bowls of water in the microwave and found that once over 60C, the PLA because quite rubbery and deformable. I then modeled a mesh to increase breathability and formability. By printing the gauntlet pieces flat and in one piece, numerous other fastening features could be incorporated directly into the gauntlet, eliminating the need for fasteners.
To test this design and process, I met up with John Wong, who had volunteered to test prototype devices and provide feedback to improve the designs. We spent an afternoon fitting and assembling a prototype and we found a lot of interesting problems to fix in the next iteration. One of the big concerns we have going forward is the long-term safety of PLA in close proximity to skin. While non-toxic, PLA filament has not undergone the same rigorous testing that medical-grade materials have. Consequently, we recommend using the mesh gauntlets in conjunction with a prosthetic “sock” to avoid direct skin contact.