Functional evaluation of a non-assembly 3D-printed hand prosthesis

Abstract

In developing countries, the access of amputees to prosthetic devices is very limited. In a way to increase accessibility of prosthetic hands, we have recently developed a new approach for the design and 3D printing of non-assembly active hand prostheses using inexpensive 3D printers working on the basis of material extrusion technology. This article describes the design of our novel 3D-printed hand prosthesis and also shows the mechanical and functional evaluation in view of its future use in developing countries. We have fabricated a hand prosthesis using 3D printing technology and a non-assembly design approach that reaches certain level of functionality. The mechanical resistance of critical parts, the mechanical performance, and the functionality of a non-assembly 3D-printed hand prosthesis were assessed. The mechanical configuration used in the hand prosthesis is able to withstand typical actuation forces delivered by prosthetic users. Moreover, the activation forces and the energy required for a closing cycle are considerably lower as compared to other body-powered prostheses. The non-assembly design achieved a comparable level of functionality with respect to other body-powered alternatives. We consider this prosthetic hand a valuable option for people with arm defects in developing countries.

Keywords: 3D printing; biomechanical testing/analysis; biomedical devices; limb prosthetics; mechanical design.

Figure 1.

Design of our 3D-printed prosthetic hand. The palm in the left picture is translucent to show the inner mechanisms (from top to bottom: leaf springs, whippletree mechanisms, and driving link), and the right picture shows the 3D-printed prosthetic hand without the palm.

Figure 2.

The experimental setup for the leaf spring ultimate strength test. The leaf spring is in its neutral configuration (left). The 3D-printed sample is under tensile and bending loading conditions during experiment. Note that the leaf spring is bent to a straight configuration, corresponding with a 90° flexion of the finger (right).

Figure 3.

The experimental setup to measure the activation and pinch forces (left). The index and middle fingers push the load cell against the thumb. The ring and little fingers meet the maximum closing angle (90°) (right).

Figure 4.

Our 3D-printed prosthetic hand attached to the simulator and a figure-of-nine shoulder harness. The cable tension that is delivered by the harness and activates the prosthetic hand is depicted (left).

Figure 5.

Our 3D-printed prosthetic hand attached to the simulator and used by the participating subjects (left) for the Box and Blocks test (top right) and the SHAP test (bottom right). Gaffer tape strips were put over the thumb, the index, and middle fingers to increase grip (right).

Figure 6.

A load versus displacement response for five samples of the leaf spring configuration.

Figure 7.

The results of the mechanical assessment of the prosthesis. Cable displacement versus the input force for five closing–opening cycles (left), and a representative trial of the input force versus pinch force including commercially available prostheses subjected to the same testing protocol (adapted from Smit and Plettenburg and Smit et al.) (right).

Figure 8.

Scores during the BBT in four trials for the 3D-printed hand without any modifications (left) and the 3D-printed hand with friction enhancement (right).