(L-457) Responsive Transtibial Ankle Prosthetic Implementing Muscle Wire for Amputees in Developing Countries

Introduction:: There are over 40 million amputees within the labor-intensive workforce of developing countries. Only 5% to 15% of these amputees, however, are able to receive prosthetics due to significant costs and a lack of available resources [1]. Current prosthetic solutions do not allow for motion of the ankle joint, leading to improper gait mechanics and further injury, thus putting a pause on daily work. In most cases, physical labor is an essential part of life in developing countries and vital for survival; therefore, it is imperative to develop an affordable and mobile prosthetic that can withstand the environment of farming communities. Our ankle prosthetic aims to meet this need by incorporating the natural shape and structure of a foot with a novel system of muscle wires and sensors to allow for ankle mobility and adaptation to changes in terrain with hopes that amputees may return to daily activities and do so pain-free.


Materials and Methods:: Our ankle prosthetic was designed and rendered in SolidWorks using the work of Masum et al. as a model [2]. The kinematics of the foot were evaluated with Simulink and compared to current ISO standards for ankle prosthetic devices. The ball and socket design provides movement in the sagittal and lateral plane while the muscle wire, a nitinol shape memory alloy that contracts and lmk extends when activated with electrical current, is placed in spring form along the joint area to pull the foot into different positions. The springs along the prosthetic’s talocrural joint absorb shock in the coronal and sagittal plane, and the muscle wire controls the dorsiflexion and plantarflexion movements. All components in the design have been carefully selected to endure heat, dirt, and humidity. The pressure sensors attached to the sole of the prosthetic observe foot position and communicate with the prosthetic’s Arduino controller which emits a responding current that is conducted through the muscle wire. Flex sensors are also placed on the outer edges of the foot to detect imbalances in the transverse plane and allow for corrective motion of the ankle joint when walking on uneven terrain.

Results, Conclusions, and Discussions:: The prosthetic provides access to a full range of motion while the base of the foot absorbs shock to promote gait kinematics patterns. The force, stress, and cyclic loading analysis in SolidWorks determined that the design is capable of withstanding 9,000N of force with a lifetime of 2 years. The muscle wire is responsible for the motion of the prosthetic and must exert sufficient force to lift the prosthetic foot when electrically stimulated. Mechanical testing was conducted on the muscle wire in its normal state and under a supplied voltage to evaluate its effectiveness and performance as a method of actuation in the ankle prosthetic. The results demonstrated that the muscle wire specimen can undergo an average of 232.36N of force before fracture and, between 1 and 1.5V, it can still withstand an average of 239.03 N of force. This evidence supports that nitinol can replace a motor in ankle joint while increasing ankle functions for transtibial amputees. The optimal placement for the pressure sensors was determined by referencing FEA analysis of plantar pressure distributions which were translated to the current prototype. The pressure sensors have been placed on the bottom of a 3D printed prototype and coded through an Arduino circuit to indicate time points of high, low, and medium pressure on different areas of the prosthetic foot. The sensors will stimulate a certain electrical voltage to pass through the muscle wire causing it to contract, pulling the foot into dorsiflexion and plantarflexion movements.


This ankle prosthetic addresses the need for an affordable and durable assistive device while offering the dynamic capabilities generated by the muscle wire components and informed by the pressure sensors. The next phase of the project will involve investigating the change in length of the muscle wire in response to varying voltages to determine the amount of voltage needed at each phase of the walking cycle to achieve the desired angles of flexion during a normal walking cycle. Further steps would also include physical gait analysis studies, and implementation of the flex sensors to provide corrective motion for the foot while walking on uneven terrain.


Acknowledgements (Optional): : This work was financially supported by the Clemson-IIT Center for Innovative Medical Devices and Sensors, CECAS TIGER grant program, Clemson Honors College, and Clemson Creative Inquiry. The authors gratefully acknowledge Dr. Sandeep Jha, Dr. Deepak Joshi, and Dr. Richa Sharma for their support on this project. Katherine Summers, Isabella Museck, Kaitlyn Cimney and Kendall Winston are also acknowledged for their undergraduate research work on the project.

References (Optional): : [1] Martin Marino, M.M., Access to Prosthetic Devices in Developing Countries: Pathways and Challenges. 2015. 1-2.

[2] Habib Masum, H.M., Conceptual Design of a Powered Ankle-Foot Prosthesis for Walking. 2014, 229-231