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Scan-and-Solve Pro Analysis on Prosthetic Feet

Introduction

Prosthetic feet give amputees the ability to walk, run, and participate in everyday activities again. Over the past decade, technology and research have expanded the functionality of prosthetic feet so that there are now a wide range of feet to choose from. The heavy wood and steel materials that were previously used have been replaced by lightweight plastics, metal alloys and carbon fiber composites [1]. In this study I show how different prostheses compare mechanically. To do this I used three different designs of a prosthetic foot shown in Figure 1 below. Design 1 is created to allow amputees to participate in sporting activities and is ideal for running whereas designs 2 and 3 are created to provide support and protection for less active amputees [2].

Table 1: The three designs of prosthetic feet used in this study.

Design 1

  • Allows for quick return of energy to achieve higher speeds, great for sprinting
  • More difficult to learn how to use
  • Need to have enough strength in order to make this kind of foot energy efficient [3]

Design 2

  • Increased ground contact allows more symmetrical gait
  • Improved stability and safety on uneven terrain
  • Reduced socket pressures for the residual limb [4]

Design 3

  • Toe up allows for swing through clearance and a natural position for sitting [5]
  • Toe and heel springs
  • Two prongs allow for the aesthetic benefit of being able to wear sandals between toes

In order to test how the three different foot prosthetic designs compared to each other mechanically, I performed simulations on Rhino using Scan&Solve Pro. The material used in these simulations was ABS. This was chosen because it is a common material that is used in 3D printing and it was found to have already been used for a 3D printed foot prosthetic [6]. The restraint was put on the top of the prosthetic, where it would be connected to the patient’s leg. A 900 N force was applied to the bottom of each of the prosthetics in 3 different positions(heel strike, midstance, and push off) based on the walking gait cycle as seen in the results below. By keeping the load constant across the designs, it allows us to study their relative performances.

Results

Design 1:

Design 2:

Design 3:


Conclusion

The differences between the three prosthetic foot designs in mechanical displacement and von mises stress are shown above. The same magnitude of force was used on each design and design 1 showed significantly lower von mises stress values. The results confirm that design 1 is stronger and better for strenuous activities such as running due to its lower stress. The design is able to distribute the force more evenly over the foot than the other two designs. It is very important for the amputee to have a prosthetic foot that can support their lifestyle. Therefore, the use of the Scan&Solve Pro is a useful tool to use on the foot prosthetic model before it is sent to be 3D printed. A simulation can be run in order to test for any weaknesses in strength in the design. The ability to 3D print customized prosthetic feet allows amputees to receive prostheses that better fit to their leg and their lifestyle.

References

[1] Amputee Coalition. (2018). Prosthetic Feet - Amputee Coalition.

[2] Medicalexpo.com. (2018). Prosthetic Foot - Össur.

[3] Prosthetic Running. (2018). Optimal Prosthetic Components for Running.

[4] Freedom Innovations. (2018). Kinterra Foot/Ankle System.

[5] Endolite USA - Lower Limb Prosthetics. (2018). Echelon - Carbon, Feet, Hydraulic, Waterproof Feet - Endolite USA - Lower Limb Prosthetics.

[6] Rochlitz, B. and Pammer, D. (2017). Design and Analysis of 3D Printable Foot Prosthesis. Periodica Polytechnica Mechanical Engineering, 61(4), p.282.

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