Professor Florida Gulf Coast University Fort Myers, Florida, United States
Introduction: The current running legs for amputees can be made from costly materials such as carbon fiber, which might be an expensive choice for amputees in the market, preventing them from buying a desired prosthesis (Poonsiri et al., 2020). Additionally, a running prosthetic leg may require time for the amputee to adjust to the functionality of the limb. The focus of this study is to develop a 3-D printed running prosthetic that serves to be a cheaper alternative to more expensive limbs on the market. With a cheaper option, it may allow amputees to get comfortable with this style of leg without spending a significant amount of money.
Materials and
Methods: To develop a low-cost running prosthetic, CAD models were made in SolidWorks. During this stage of development, we are aiming to achieve a factor of safety (FOS) of 2+ under 2000 Newtons applied in the vertical direction with 80 mm (about 3.15 in) of displacement. A force of 2000 Newtons was tested in the anterior and lateral directions as well, as the device should be more stiff in these direction than in the vertical direction. Additionally, we want to take note of where the most stress is during simulations, helping to revise our model to displace the correct amount without breaking under the desired load. 80 mm of displacement was chosen so we can compare our results with commercially available running prosthetics, including the Ossur Flex-Run, Freedom Innovations Catapult FX6, Ottobock 1E90 Sprinter, and the Ossur Cheetah Xtend. To represent the results of the vertical loads, displacement simulations are visualized, and a table is used to represent the results of the vertical, anterior, and lateral loads.
Results, Conclusions, and Discussions: With the first design, the issues included exceptionally low FOS and displacement. The initial intention was to stabilize the foot with two additional support beams running to the toe section. However, given the thickness and how rigid the part is, this was not optimal because the factor of safety was far below the desired amount. In the second design, the additional beams were removed and the foot was extruded further, but as seen in Figure 2 the design allowed for a significant displacement of the foot as it was putting excessive stress on one portion of the curve rather than equally dispersing the load. With a new geometry and the addition of a truss structure, the third design saw an increase in the FOS and reduced displacement. The intention of design 3 was to help disperse the load throughout the foot, with the truss design meant to soften the parts we wanted to bend. Additionally, with an elongated curve, the stress was not exclusively in one portion of the blade. A fourth design was made to increase the stiffness in the anterior and lateral directions. In doing so, we were successful in increasing stiffness in these directions, but the displacement in the vertical direction seemed to decrease below the desired amount of 80 mm. Future testing would involve 3-D printing the simulated part and test the deformation on the Intron. The top portion of the blade would attach to the Instron, and the curved bottom portion of the blade would be placed on the floor of the machine along with a block to prevent sliding. We intend to test the foot at a constant loading rate as well a loading rate of 100 N/s, three loads would be tested to simulate different conditions such as standing (700 N), (1400 N) walking, and running (2100 N).
