Parametric Design and Additive Manufacturing of Low-Cost Prosthetic Hands with Shape-Adaptive Grasp

Upper-limb amputation profoundly affects individuals’ quality of life by severely limiting their ability to perform Activities of Daily Living (ADLs). Although robotic hand prostheses offer partial functional restoration, their high abandonment rate remains a critical challenge. This is largely due to limitations in functionality, unsatisfactory aesthetics, excessive weight, high costs, challenges in maintenance, and insufficient user training. User-centred design requirements emphasise anthropomorphism, in terms of size, weight and shape, and the capability to support the most common ADLs. However, commercial prosthetic solutions often lack adaptability and remain prohibitively expensive. Additive Manufacturing (AM) has emerged as a promising solution to reduce production costs and enhance customisation, thus potentially improving the usability and acceptance of prosthetic hands. Nevertheless, few AM-based prosthetic devices incorporate linkage-driven mechanisms capable of preshaping and shape-adaptive grasping, both essential for functional and natural interaction with objects. This thesis aims to address three main challenges associated with prosthetic hand rejection and diffusion: anthropomorphism, affordability, and grasp adaptability. The thesis proposes: i) a cost-effective manufacturing pipeline through the selection of appropriate AM technologies and materials; ii) a parametric 3D model for custom linkage-driven under-actuated prosthetic hands based on human anthropometry, rapid scaling and customisation; and iii) a novel method that integrates compliant elements into linkage-driven fingers to enable inter-phalanx Shape Adaptivity (SA) behaviour and improve grasping performance, without increasing bulk and preserving human-hand-like dimensions. An extensive review of AM technologies and material properties was conducted, highlighting their respective suitability for functional prosthetic applications. A novel parametric 3D model of a linkage-driven prosthetic hand was developed, featuring internal linkages and anatomically shaped shells. Three standard sizes based on anthropometric data have been defined, with further customisation possible through 3D scanning of the amputee's contralateral hand. The 3D model incorporates constraints imposed by manufacturing techniques. The structural integrity of the device was assessed through Finite Element Method (FEM) simulations, and the fidelity of the design was validated through geometrical \R{and dimensional} deviation analysis. A kinematic evaluation confirmed the similarity of the prosthesis biomechanics compared to human references. To address SA, a novel approach based on multi-material 3D printing (MMP) was developed, enabling the integration of mechanically compliant elements within the linkage-driven prosthetic hands. This approach was experimentally validated through mechanical testing using an Instron Universal Testing machine, demonstrating the mechanical reliability of the compliant elements. Their integration into the linkage-driven prosthetic hand enabled shape-adaptive grasps. A kinematic acquisition has been performed to verify the adaptation of fingers to the object, increasing the stability of the grip. In conclusion, this thesis provides a comprehensive, engineering-driven response to the challenges of anthropomorphism, cost, and functionality in hand prostheses, advancing the field toward more accessible, acceptable, and adaptive prosthetic hands.