Abstract
Various upper-limb prostheses have been designed for 3D printing but only a few of them are based on bio-inspired design principles and many anatomical details are not typically incorporated even though 3D printing offers advantages that facilitate the application of such design principles. We therefore aimed to apply a bio-inspired approach to the design and fabrication of articulated fingers for a new type of 3D printed hand prosthesis that is body-powered and complies with basic user requirements. We first studied the biological structure of human fingers and their movement control mechanisms in order to devise the transmission and actuation system. A number of working principles were established and various simplifications were made to fabricate the hand prosthesis using a fused deposition modelling (FDM) 3D printer with dual material extrusion. We then evaluated the mechanical performance of the prosthetic device by measuring its ability to exert pinch forces and the energy dissipated during each operational cycle. We fabricated our prototypes using three polymeric materials including PLA, TPU, and Nylon. The total weight of the prosthesis was 92 g with a total material cost of 12 US dollars. The energy dissipated during each cycle was 0.380 Nm with a pinch force of ≈16 N corresponding to an input force of 100 N. The hand is actuated by a conventional pulling cable used in BP prostheses. It is connected to a shoulder strap at one end and to the coupling of the whiffle tree mechanism at the other end. The whiffle tree mechanism distributes the force to the four tendons, which bend all fingers simultaneously when pulled. The design described in this manuscript demonstrates several bio-inspired design features and is capable of performing different grasping patterns due to the adaptive grasping provided by the articulated fingers. The pinch force obtained is superior to other fully 3D printed body-powered hand prostheses, but still below that of conventional body powered hand prostheses. We present a 3D printed bio-inspired prosthetic hand that is body-powered and includes all of the following characteristics: adaptive grasping, articulated fingers, and minimized post-printing assembly. Additionally, the low cost and low weight make this prosthetic hand a worthy option mainly in locations where state-of-the-art prosthetic workshops are absent.
Highlights
The demand for prosthetic limbs is rising as the number of amputations is increasing worldwide
We continued our design by establishing a number of basic requirements for the hand prosthesis based on the work by Plettenburg[27]: bodypowered (BP) control, cosmetic appearance, light weight, and water/dirt resistance
The hand is actuated by a conventional pulling cable used in body powered (BP) prostheses that is connected to the coupling of the whiffle tree mechanism
Summary
The demand for prosthetic limbs is rising as the number of amputations is increasing worldwide. The complexity of anatomic structures in a real hand is such that prosthetic designs have to be simplified to facilitate fabrication with current technologies In this context, designers tend to disregard biological principles, instead opting for existing conventional design methods that they are confident would work and provide partial functionality of the missing body part. Designers tend to disregard biological principles, instead opting for existing conventional design methods that they are confident would work and provide partial functionality of the missing body part These conventional approaches guide the design process of most of the prosthetic hands found in the literature. Many working principles of a number of anatomical structures, like finger pads, ligaments, tendons or skin that could improve the performance of current hand prostheses, are usually not present in their designs.[4,5] One simple example is to include sliding joints similar to the ones found in the human finger instead of conventional hinged joints
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