# A Design for a 3D Printed Lower Limb Prosthetic Device ---  ###### Roberto Postelmans, founder of Humanitarian Prosthetists and Orthotists and director of ORTHOLAB --- Roberto Postelmans doesn’t give catchy names to his designs, at least not in English, but he is serious about providing low-cost prosthetic devices—both 3D printed and traditionally-manufactured—to those in need. He has been working on the design of a 3D printed prosthetic foot since he founded [Humanitarian Prosthetists and Orthotists](https://fr.hpo-lab.org/) (HP&O) in 2013, trying dozens of material combinations for the foot and insert, along with modifying infill percentages to achieve the necessary compliancy in different sections of the foot. The wide variety of new materials developed for FDM 3D printing within the last several years may now finally be used to address the pressing need for low-cost lower limb prosthetics. e-NABLE has historically focused on upper limb prosthetic devices. As we have found, this is an important niche to fill, flush with potential in both design and function. The need for low-cost upper limb prosthetic devices will not be going away any time soon. It is also an understandable niche to have settled into given the commitment e-NABLE volunteers around the world have made to “do no harm” to our recipients; lower limb prosthetics are a whole different ball game. PLA and ABS 3D printed parts have a tendency to break along layer seams and we would historically not trust parts printed with these materials to bear a heavy load or sustain repetitive stress successfully. Furthermore, distal stump of a trans-tibial or trans-femoral amputation can often not bear weight; specialized knowledge of soft socket design is needed to avoid pain or injury. As a child grows, an ill-fitting lower limb prosthetic can promote deformity; the angle that the pylon meets both the prosthetic foot and the socket are of crucial importance. It is for all these reasons and more that we have been cautious about expanding into this area of extreme need. There are far more lower limb amputees than upper limb amputees worldwide. A low-cost prosthetic paired with a knowledgeable prosthetist on the ground could be a great contribution to humanitarian health care. I would like to introduce a design for a 3D printed prosthetic foot created by Roberto that I was very interested in during my time at ORTHOLAB in [Gatagara, Rwanda](https://en.wikipedia.org/wiki/Nyanza,_Rwanda). Developed over the course of the last 6 years, child recipients in Africa up to 30 kg have received this style of 3D printed prosthetic foot from Roberto to great success.  ###### A step-by-step look at the prosthetic foot design. --- ###### The foot exterior (brown material) is printed in Filaflex Skin 2 by [Recreus](https://recreus.com/en/), an elastic filament. The foot insert (beige), providing core strength and an attachment point for the prosthetic pylon, is printed in ePA-GF by [eSUN](http://www.esun3d.net/). The ePA-GF is a glass fiber-reinforced nylon filament, with an impressive mechanical strength and rigidity. I will make a case for printing some of e-NABLE’s other prosthetic devices using this material in another post.  ###### The 3D printed prosthetic foot. Left: Top view showing length and width. Right: Side view showing height --- The design and structure of the 3D printed prosthetic foot resembles the off-the-shelf variety, but modified with features available only through production via 3D printer and at a fraction of the cost. Note the convenient separation between the first and second toes, in part to allow the recipient to wear sandals.  ###### Top: An off-the-shelf adult prosthetic foot. Bottom: ORTHOLAB’s 3D printed prosthetic foot, intended for a child. An M8x1.25 bolt is used to attach additional hardware to the prosthetic foot. --- A 15% infill in the heel provides a necessary cushioning effect as the recipient walks. The 20% infill in the toes provides a springiness that helps propel the recipient forward. The 20% infill meets the 35% infill section at the line where the proximal phalanges and the metatarsal bones meet, ensuring the toes bend where they would naturally. The 35% infill section in the middle of the foot was found to be adequate for supporting weight on the prosthetic device.  ###### The bottom of the 3D printed foot prosthetic, with labeled infill percentages at the toe, mid-foot, and heel --- The ePA-GF foot insert has a shoe-esque shape, providing as much inner structural support to the prosthetic foot as possible while still allowing the toes and heel to bend and flex as needed. The foot exterior, for its part, had a matching cavity into which the foot insert is placed. The insert has an 8 mm hole to accommodate the M8x1.25 bolt, a slightly tapered heel, and a flat top. And this material is strong! I hit it with a hammer, squeezed it in a vice, and let it fall onto concrete – it survived all three of these rigorous, highly-scientific tests.  ###### The ePA-GF 3D printed foot insert --- The heel of the ePA-GF foot insert is tapered slightly, and has a V-notch groove into which a mating tongue on inside of the foot exterior sits. To install the ePA-GF insert, the void in the foot exterior is heated slightly such that the rim becomes pliable. A screwdriver is used to provide leverage to install the insert (see video). In addition to the tight fit of the insert within the foot exterior as it cools and contracts, the tongue and groove locks the rear of the assembly into place.  ###### Left: Preparation for inserting the ePA-GF foot insert into the Filaflex foot exterior. Right: Heating the foot exterior to make the material slightly pliable prior to installation of the foot insert. --- ###### A traditional prosthetic foot is paired to a traditional socket through a pylon. The pylon could be an aluminum or plastic pipe.  ###### Examples of traditional lower-limb prosthetic devices utilizing both plastic and aluminum pylons --- At [HVP-Gatagara](http://hvpgatagara.org/), the hospital facility where ORTHOLAB is located in Southern Rwanda, the majority of lower limb prosthetics utilize the plastic pylon variety, purchased as a bagged kit from a supplier.  ###### Off-the-shelf prosthetic leg pylon kit --- The pylon is supplied in two pieces due to the individuality in length required for a specific patient. One or both of the pylon halves are cut to size and [butt welded](https://en.wikipedia.org/wiki/Welding_joint) together to form a single pylon of correct length. Half-dome-shaped alignment modules are used on both the prosthetic and socket ends to precisely set the angles that the recipient needs in their particular case.  ###### Off-the-shelf prosthetic leg pylon kit ---  ###### A butt-welded prosthetic leg pylon sized appropriately for a recipient’s individual needs --- After the pylon halves are butt-welded together, the angles with which the pylon meets the alignment modules is set by tightening a bolt through the foot or socket, through the alignment module, and finally into the pylon itself.  ###### Left: Off-the-shelf alignment module fitted on top of the prosthetic foot. Center: The pylon’s concave end is mated to the convex side of the alignment module. Right: The concavity in the pylon contains a threaded insert into which the bolt holding securing the prosthetic foot screws into. --- Seeing a potential use case for 3D printed components, I prototyped a very simple pylon and alignment module in ePA-GF inspired by their off-the-shelf counterparts. The alignment module was flat on the bottom, mating with the top of the 3D printed prosthetic foot insert, and domed on top, mating with the concavity in the pylon. As seen in the off-the-shelf components, it is important that these pieces have a ball-and-socket-style fit, to allow the pylon to be positioned at varying angles relative to the prosthetic foot. The 3D printed pylon was very simple in design, with an octagonal exterior cross section and a hexagonal hole from the top of the pylon extending to 1 cm above the concave dome at the other end. A circular hole just large enough for the M8 bolt to slide through was modeled for the final centimeter. The octagonal shape served little purpose – it was a simple shape to use on TinkerCAD and less boring than a cylinder. The hexagonal hole allowed an M8 nut to be dropped down to rest on the ‘shelf’ created where it transitions to a circular hole. After installing the 3D printed alignment module, the pylon could be screwed down tightly.  ###### Progression of attaching the 3D printed food prosthetic to the 3D printed leg pylon --- One modification that should be made to this 3D printed prosthetic foot design in its current form is to alter the bolt hole through the foot insert to allow the bolt to sit at an angle, as in its off-the-shelf counterpart. This would help faithfully reproduce the angle-of-alignment functionality that the off-the-shelf version is designed for.  ###### Left: Top view of an off-the-shelf prosthetic foot. Note the wiggle room both back-and-forth and side-to-side, tapering down to a circular hole at the bottom of the prosthetic. Right: The bottom of the prosthetic foot. --- ### e-NABLE Community Call to Action While I was given permission to share what I learned at ORTHOLAB, with the understanding and hope that the greater e-NABLE community would benefit from this design knowledge, ORTHOLAB stopped short of providing me with the CAD files for the foot exterior and foot insert. These should not be very difficult for members of the community skilled in CAD modeling to reproduce. If anyone is looking for a project, please consider designing an e-NABLE version of this prosthetic foot design and contact me if I can answer any questions that would help faithfully reproduce the design. In addition to fully 3D printed pylons and alignment modules, e-NABLE volunteers could have the opportunity to spearhead the development of 3D printed modules which could interface with aluminum pipe, a common material around the world. **A word of caution:** If e-NABLE is to move toward including lower limb prosthetics options to potential recipients in high-need areas, so too must we partner with trained prosthetists to ensure proper fit of traditionally-made or 3D printed sockets in those areas. As important, a trained prosthetist can help safeguard against potential deformities associated with improper loading on the residual limb in the growing child, which is less of a concern in adults. I believe e-NABLE could do substantial good in the world by identifying established humanitarian prosthetists around the globe to work directly with, such as Roberto from HP&O as well as Rajab Hamis from [Lake Victoria Disability Center](http://lakevictoriadisabilitycentre.org/) (LVDC) in [Musoma](https://en.wikipedia.org/wiki/Musoma), [Tanzania](https://en.wikipedia.org/wiki/Tanzania). e-NABLE could provide distributed manufacturing of specific prosthetic devices and accessories, sending these devices to the prosthetists on the ground in these high-need areas. The responsibility for providing high-quality 3D printed prosthetic components falls on the shoulders of the e-NABLE community, and the responsibility of ensuring a proper fit falls to the prosthetist.