Abstract. The objective of this paper is to find an alternative material to develop cheaper prosthetic limbs.  In this experiment, three different materials were 3D printed using an Ulitmaker 3 and tested using an Interactive Strength Challenger: Polylactic acid (PLA), Acrylonitrile Butadiene Styrene (ABS), and Nylon. Nylon proved to be the most effective through tensile and compression tests, yet further experimentation is necessary to develop a full conclusion on its applications.

Introduction. Biomedical engineers are currently searching for cost-effective yet strong alternative materials to manufacture prosthetics for amputees who cannot afford the cost of traditional devices. Since cost of materials is a priority, the materials included in this experiment (Polylactic Acid, Acrylonitrile Butadiene Styrene, and Nylon) are readily available, affordable, and abundant. Besides the tensile and compressive strength of the materials, significant factors such as heat resistance and printability must also be considered. Although there is limited information available on nylon in 3D printing, its properties determined by Mostafa, Qureshi, and Montemagno (2018) prove it to be a main candidate in this experiment. This paper examines the properties, specifically the tensile and compressive strength, of 3D printing plastics to establish the most durable and supportive material for prosthetic limbs.

Experimental Details. Designing the test models included the use of Mastercam 2020 after measuring the entry points of the Interactive Strength Challenger (ISC) machine. Models for the tensile strength test measured 0.9944 in. by 2.8358 in. by 0.1205 in. while models for the compression test consisted of an upside-down cone with an indentation on top of a cylinder. The base measured 0.299 in. by 0.6055 in. and the top shape had a radius of 0.5 in and a depth of 0.35 in. The program was then transmitted from a desktop to the printer with the use of a USB flash drive. Each of the shapes were printed using rolls of different materials (ABS, PLA, and Nylon) loaded into an Ultimaker 3. The models were then tested using the according apparatus in the Interactive Strength Challenger. The ISC Materials program allowed for the modification of settings and the collection of data.

Results and Discussion. The outcome for the tensile strength of the materials ranged from about 12.5 ksi to 21.7 ksi. During tensile strength testing all the materials broke in the upper area connecting a thinner piece and a box. Nylon proved to manage the most amount of stress as compared to the other materials in both compression and tensile examinations (Figure 1 -2) which was originally hypothesized. Nylon although a strong material absorbs a slight amount of moisture which can limit its productivity and is of concern to regions in warm climates. The PLA plastic performed well and can be considered as another alternative to nylon; however, more effective materials and products are preferred. All the materials were able to withstand over 600 pounds of pressure (Figure 2) which eliminates the concern of the patient’s weight. This experiment does not include results or reports of a compression test on ABS plastic due to the failure of the Ultimaker 3. Although this area of data is missing, ABS would not have been considered due to its poor performance in the tensile test. Laboratory reports of Mostafa, Qureshi, and Montemagno (2018) portrayed the strength and durability of Nylon plastic which this experiment proves accurate.

Figure 1. Describes the tensile strength for each material.

Figure 2. Describes the compression strength for each material.

Conclusion. This experiment determined the tensile and compression tests on varying 3D plastics to find a cheaper alternative to carbon fiber prosthetic limbs. The best material option would be nylon due to its performance during testing and its heat resistance. In order to fully analyze the effectiveness of nylon, further testing is required especially of its compression strength and behavior to warmer climates. As biomedical engineering for prosthetic limbs spreads to particularly second and third world countries, it is essential to develop a practical material alternative to amputees of lower socio-economic class.

Acknowledgments. I would like to thank Ramses Gonzalez for offering me the opportunity to conduct this research and Paul Kynerd for instructing me on the use of the equipment. I would also like to acknowledge Miami Lakes Educational Center for providing the necessary funding for all of the necessary machines and tools.

References.

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     (2) Mostafa, K. G., Montemagno, C., & Qureshi, A. J. (2018). Strength to cost ratio analysis of FDM Nylon 12 3D Printed Parts, 754–761. doi: 10.1016/j.promfg.2018.07.086

     (3) Nylon. (n.d.). Retrieved October 14, 2019, from http://www.plasticmoulding.ca/polymers/nylons.htm.

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