Accessible Hand Prostheses: 3D Printing meet Smartphones

Abstract

The World Health Organization (WHO) estimates that there are ≈40 million amputees in developing countries and that only ≈5% of them have access to prosthetic devices. In low income countries, there are only a few big cities capable of providing reasonable healthcare services and transportation from rural areas is usually complicated, expensive, and may take several days. In most of the cases, there is a general lack of trained personnel and materials making, prosthetic workshops limited, difficult to reach, or even non-existent. 3D printing is a manufacturing method that enables fabrication of structures with unusual geometries without the need for any particular manual skill, elaborate tooling, or labour-intensive procedures. Many 3D printing techniques have become easily accessible and have opened a window for creating low-cost functional parts in a simpler way than conventional procedures. The main purpose of the research described in this thesis is to increase the accessibility of prosthetic hands among people living in low-income settings. To achieve this, the goal of the research is twofold: one, to design a transradial hand prosthesis that can be 3D printed with very few and simple post assembly steps and suffice basic user requirements; and two, to develop a 3D modelling process based on 2D photographs for the design of transradial (below the elbow) sockets that can be 3D printed. This thesis began exploring possibilities of non-assembly fabrication using 3D printing techniques. Chapter 2 contains a literature review describing a number of mechanisms fabricated in a non-assembly manner by 3D printing. Chapter 3 reviews the results of fatigue testing in 3D printed polymers in order to determine the 3D printing material and 3D printing settings that ensure best fatigue performance. Chapter 4 continues with a number of design considerations that were formulated for the fabrication of non-assembly mechanisms with 3D printing. We followed these guidelines to design a functional multi-articulated hand prosthesis that was then manufactured by material extrusion 3D printing. This design procedure concluded in a hand prosthesis concept that reduces manufacturing requirements to a single 3D printer and its building material. Chapter 5 contains a functional evaluation of the 3D printed prosthetic hand including mechanical and user testing. To further explore the capabilities of non-assembly 3D printing, in Chapter 6 we initiated a new design process aimed at producing articulated fingers (two degrees of freedom per finger) under this manufacturing framework. For this process, we adopted a bio-inspired design approach by studying the anatomical structures of the human hand that can be translated into components of prosthetic hands and have the potential of offering improved functionality. This bio-inspired designed prosthetic hand achieved superior pinch force as compared to our previous non-assembly BP prosthetic hand. Chapter 7 describes the method employed to obtain and process the 3D models of a stump. The method is based on photos from a smartphone and a Statistical Shape Model (SSM). The algorithm translates the photos into a 3D digital shape and then introduces the digital outcome into the process of automatic anthropometry. The outcome was later used for determining the parameters of a parametric design of a transradial socket that can be 3D printed and fitted onto the user’s residual limb. The error resulting from the automatic measurement was still too large for an acceptable socket design. The thesis ends in Chapter 8 with a pilot study of our new bio-inspired 3D printed hand design in Colombia. We employed a manual measuring method using visual cues of the stump and a measuring tape to obtain the dimensions required for the design of the socket. Through the manual measuring method and parametric socket and shaft designs, the components of the prosthetic device were produced easily and locally on a material extrusion 3D printer. The field testing in Colombia concluded that our design and manufacturing processes based on 3D printing are fast and easy to implement and opens a gateway for the production of prosthetic devices in developing countries.