Researchers in Brazil have published a study aiming to improve the characteristics and accessibility of robotic mechanical prosthesis with 3D printing.
Mechanized prostheses have the potential to provide a viable low-cost alternative for simulating the functions lost by disabled people. However, it’s high value means these devices have low purchasing power, rendering them inaccessible.
In their paper, the researchers detail the use of 3D printing to improve upper limb mechanical prosthesis with anthropomorphic characteristics implemented through programming, while importantly focusing on ensuring a low financial cost for the device.
Increasing the accessibility of medical devices using 3D printing
The study first sets out detailing the state of the current market for prostheses. Although the development of such devices for the rehabilitation of amputees has been evolving, the researchers explain mechanical prostheses have a commercial disadvantage. “The prices charged for these prostheses are above the acquisition conditions for a large part of the population undergoing rehabilitation. The purchase of a prosthesis by people with low acquisition value ends up not being viable, and thus, they opt for non-automated mechanisms with low mechanical control and interaction with the user.”
In view of the problem, the study then positions 3D printing as a potential technology for designing effective prostheses with low cost: “It is possible to print models with characteristics similar to those of humans, giving it the ability to approach the resourcefulness of real human parts.”
Indeed, 3D printing has been used to help increase the accessibility of customized medical devices such as prostheses for amputees around the world. Recently on 3D Printing Industry we detailed how 3D Sierra Leone, a Dutch nonprofit organization, is providing customized 3D printed prostheses to patients in the West African country. Using 3D printing, 3D Sierra Leone is dedicated to improving the lives of people in Sierra Leone that undergo amputations but are without access to relevant medical care.
In Syria, 3D printing is also being leveraged to provide prostheses as traditionally manufactured devices have been difficult to source amid the ongoing Civil War. The likes of Syria Relief, a UK-based charity working in Syria, has pleaded with the UK’s Department for International Development (DFID) to provide funding for 3D prosthetics for children in the country.
3D printing mechanical prostheses
In their work presenting the development and improvement of upper limb prosthesis with anthropomorphic characteristics and low financial cost, the researchers use 3D printed parts alongside electromyography (EMG) sensors and strain gauge force sensors.
The design of the prosthesis was modelled in AutoDesk CAD software, before being 3D printed using an AnetA8 3D printer. As the AnetA8 is a low-cost system, it is not equipped with depth sensors to detect the approach of the extruder nozzle to the table, which can lead to a collision. As such, the researchers opted to modify the system, by implementing an inductive sensor for detecting metallic materials, and updating the firmware and calibration.
Each of the components on the prosthesis were designed to interact mechanically, equivalent to the bone structure present in the composition of the human hand, which is composed of 27 bones. “Thus, at the end of the modeling of the structures, the equivalent of 37 pieces was reached, all of them structured so that it was possible to pass internal cables to perform the movement of the fingers during an action.”
The internal structure of the prostheses included perforations of 2mm in diameter in order to allow the passage of cables through the device. The fist was attached to the hand and fingers using steel screws, and hard copper was utilized for connecting finger links.
The researchers selected PLA as the material for 3D printing in the first phase due to its 190°C melting point. Parameters for the 3D printing process were established using Simplify3D V4.1 software, in order to determine the amount of filament needed, and length of the printing process. To enable movement of the prosthetic fingers, high torque 13 kg / cm servo motors were used when powered at 4.8v, with 4.8 – 7.2 V operating capacity. The metal gears allow for less wear and great reliability in torque during the movement of the fingers. To measure the pressure of the fingers on the surface of the palm, the use of a force sensor with a measuring range between 100 grams to approximately 10kg was adopted, with a detection area of 15 mm in a circular format.
When testing the capabilities of the device, the researchers explained: “The sensory application proved to be satisfactory in view that the results measured between the prosthesis and the target musculature, were measured and converted into movements for the equipment. Thus, the force sensor was able to stop the movement, preventing the fingers from closing in such a way as to damage the joint structure of the prosthesis.”
The final acquisition value of the project amounted to R$ 2,000 ($374), compared to the current market average of approximately R$ 200,000 ($37408) for mechanical prostheses.
Concluding the paper, the researchers detail how the research into affordable 3D printed mechanical prostheses can progress: “Aiming at future studies involving the improvement project of mechanical prostheses, sensors that may simulate the touch of a surface similar to human skin may be provided, as well as the insertion of new force and EMG sensors to better treat the stimulus signals dissipated in the muscle ventricle.”
The paper, “Prototype of robotic mechanical prosthesis of upper limb at low cost” is published in International Journal of Advanced Engineering Research and Science. It is written by Thiago A. do Carmo, Regina E. S. Cabette and Renato G. Gomes.
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Featured image shows a comparison between real model (left) & Developed in this work (right). Image via International Journal of Advanced Engineering Research and Science.