3D Printing Pediatric Prosthetics

Contributed by our Fall 2020 Undergraduate Student Sophie Naud

e-NABLE is a global community of volunteers who work to provide free and low-cost prosthetic upper-limb devices to those in need in underserved communities or without access to medical care. Using 3D printers and open-source designs created by volunteers, e-NABLE volunteers have provided an estimated 8,000 devices in over 100 countries to individuals who have lost or who were born without hands or fingers. This semester, as part of a group of five female Biomedical Engineering students at Yale, I aimed to establish a Yale chapter of e-NABLE to provide needed prosthetic devices to individuals in or around New Haven, CT using campus resources. However, before becoming a certified chapter, as many members as possible needed to be certified in the fabrication and assembly of e-NABLE devices by making and submitting pictures and videos of functional test hands to the organization.

As a founding board member, I set out to make my first test hand and earn my Fabrication and Assembly Badges, demonstrating that I can properly print and assemble a device and am qualified to create devices for distribution to those in need. For my test hand, I planned to print the Phoenix Unlimbited model, a prosthetic hand that uses the force of the wrist bending to close the fingers and form a fist. However, as a sophomore at Yale who was not allowed to return to campus this fall due to COVID-19, I was taking online classes and living in an Airbnb in Mount Pleasant, SC for the semester with no access to a 3D printer or any other campus resources. I took to the internet and was lucky enough to come across Dr. Badran’s contact information at the Neuro-X Lab, and he was kind enough to both mentor me in 3D printing and teach me a bit about his work in the Brain Stimulation Lab. 

“I learned to manipulate printing options like temperature, position, rafts, infill, and more, and I practiced by printing a series of small objects like cones and dice of different sizes in both PLA and ABS.”

With no prior 3D printing experience, I spent this semester learning the in’s and out’s of two different types of 3D printing, extrusion and resin, and I can now say I am well-versed in both. I began my work with Dr. Badran by printing on his seven-year-old Flashforge Creator Pro with a faulty right extruder. I learned to manipulate printing options like temperature, position, rafts, infill, and more, and I practiced by printing a series of small objects like cones and dice of different sizes in both PLA and ABS. From these practice objects, I determined PLA to be the best material for the main parts of my test hand, as it has a clean finish and precise detailing, and due to its lower printing temperature, PLA can be thermoformed, as required by parts of the test hand. However, I used ABS for the joints and pins of the hand, which require a stiffer material to ensure the stability and durability of the hand, but they came out with some slight imperfections in print quality. At the same time, I printed a resin version of the test hand on a Formlabs Form 2 printer. After practicing with cones, similarly to my practice on the extrusion printer, I was able to position almost every piece required for the test hand on the platform in one print. I left it overnight and almost the entirety of the hand was printed by morning. Of course, I still had to clip off the supports and cure the pieces in rubbing alcohol and UV light, but the process was practically one and done, leaving me with a set of beautifully printed pieces. However, assembly with resin pieces was much more difficult, as the pins fit too tightly in the joints, and they had to be sanded down with a Dremel tool in order to assemble the pieces. Additionally, while indeed strong and durable, the cured resin hand parts were unable to be thermoformed, so I had to print certain pieces in PLA and create a hybrid resin and PLA hand.

Fully assembled hand

Shortly after beginning the printing of the hand pieces, I took the 3D printer home on loan and began to carry out my semester-long project independently. I indeed ran into many challenges, especially using such an aged printer, but I learned to troubleshoot and solve problems on my own and got to experience the rewarding feeling of overcoming those setbacks. For example, when printing the palm piece of the hand, the curved top part of the piece repeatedly caved in, but by altering the temperature and speed of the print, adding specific supports, and changing the palm’s orientation, I was able to successfully print a high-quality palm piece. Eventually, after many attempts at some of the pieces, I ended up with a palm, finger and joint pieces, pins to assemble the fingers and attach them to the palm, and a gauntlet to mold around the wrist with an attached box for tensioning. With everything printed and prepped, I began to assemble the hand using orthodontic bands, screws, sewing thread, and medical foam. I first assembled the fingers with pins and attached them to the palm, and I added medical foam and thermoformed the palm for additional wearing comfort. Next, I thermoformed the gauntlet to the shape of a wrist using boiling water and a mold made from the resin printer, and I added medical foam to the inside of the gauntlet as well. I added orthodontic bands to every joint to act as ligaments, and I screwed in tensioner pins to the box on the gauntlet and threaded the sewing thread through the channels in the palm as a tendon system, tweaking the screws to get it just right. Finally, I added velcro straps to hold the hand in place on the wearer. In my completed hand, there was still a bit of friction restricting finger movement, so Dr. Badran assisted me in adding a dry teflon lube to the joints, and it worked like a charm. The final product was perfectly functional; when you bend the wrist down, the fingers curl to form a fist, and when you bring the wrist back, the fingers spring back to extend again. Upon submitting evidence of my successful test hand to the national chapter, I have received both the Fabrication and Assembly badges for the Phoenix Unlimited model, and I will be able to use what I have learned to assist others in creating test hands as well.

“The final product was perfectly functional; when you bend the wrist down, the fingers curl to form a fist, and when you bring the wrist back, the fingers spring back to extend again.”

What’s Next for Sophie…

In the spring, I will be returning to Yale’s campus in New Haven, CT, where I will continue to take classes and pursue a joint B.S./M.S. degree in Biomedical Engineering. In addition to my work with e-NABLE, where I will continue to serve as a Project Manager, in which I spearhead the member badging process for test hands, serve as a point of contact for Assembly and Fabrication teams, and oversee the prototype to delivery timeline for device development, I am also Chief Administrative Officer of a biotech startup called Simplex Sciences, Inc. Simplex specializes in the production of single-stranded ssDNA ladders for academic and industrial institutions (e.g. GRAIL, MIT, Novartis) on an international scale. Additionally, with e-NABLE, I am a Project Manager on our new project recently termed “The Cello Project.” After being sought out by a local 10-year-old girl’s father through Yale, my team took on the challenge to develop a cello bow adapter for Emily, an aspiring cellist with no left hand. This adapter, designed by my team, will connect her current prosthetic hand to the cello bow, which will vastly improve her current, makeshift adapter and help Emily achieve her musical dreams. I am looking forward to continuing to work to create devices for those in need with e-NABLE, and I am thankful for the tools I have learned by working on this project with Dr. Badran this semester.