Parametric design of a 3D printable hand prosthesis for children in developing countries

Abstract

In developing countries amputation surgeries are performed more often than in western countries due to a lack of medical knowledge and the prevalence of illnesses that have been defeated in the developed world. Only 5% of the amputees own a prosthesis because there are distribution and maintenance problems, as well as cultural issues surrounding the reputation of amputees, therefore only a few of the available devices are used. It is very important to have a prosthetic hand that resemble the real human hand to avoid discrimination and exclusion from the society. This is especially an issue for children due to the fast changing anatomy. The aim of the project is \textit{to develop a generalized 3D printable body-powered prosthetic hand design for children in developing countries that allows parametric design}. The advantages of parametric design is that it can be personalized for every user and every child can be fitted with a prosthesis that most resembles the size of his/her sound hand. A statistical analysis has been conducted to understand which parameters are the best choice for a parametric design. Starting from 8 parameters, only four were found important to draw a prosthetic hand (grip circumference, palm breadth, thumb breadth and palm length), while the others can be connected to the main ones. It was possible to connect all the parameters, including the four main ones, to a single parameter (palm breadth). The design was done in Solidwork and it was connected to an external file that allows to change and adapt the design without needs to open the CAD file. The hand is body powered and it is activated with a lever that, when pushed, closes the fingers. Elastic bands reopen the hand when the tension on the lever is released. The connection between the moving part (fingers) and the fixed part (palm and thumb) is a sliding curved joint, considered the best option due to the easiness of printing and similarity with a human hand. It was found that the best printing strategy is to print the device into 3 parts and then connecting it with glue and elastic bends. The prosthesis was successfully 3D printed and it fulfilled all the requirements concerning price, weight and hand shape. The device is required to support a pinch force of 10 N and mechanical tests proved that it is able to provide force up to 35 N for a child of 13 years old. User testing showed that the hand is as functional as already existing devices and that it can perform daily activities. The main problem of the hand is the durability, which needs to be improved with studies regarding support and printing strategies. Future work is needed to design a 3D printable wrist and socket.