Enhancing the Effectiveness and Availability of Orthoses by Additive Manufacturing

The health of the musculoskeletal system is critical for locomotion function, yet globally, approximately 1.71 billion people suffer from musculoskeletal conditions. Ankle inversion sprains are the most prevalent acute injuries, causing temporary mobility restrictions and long-term residual ankle symptoms. Ankle foot orthoses (AFOs) are the primary intervention for treating and preventing recurrent sprains by providing timely external mechanical support to the ankle joint. However, traditional AFOs are often rigid, heavy, and ill-fitting due to their one-size-fits-all design and the time-consuming and costly manufacturing process required for customisation. While 3D printing provides a more rapid and cost-effective approach for fabricating custom-fit AFOs, the current 3D-printed AFOs remain bulky and rigid owing to their limited design and the use of low-stiffness materials, thus still restricting the natural ankle movements, leading to discomfort and potential muscle contractures after prolonged wearing. This thesis proposes a novel ankle inversion brace that is flexible, lightweight, customisable, yet high-performance. It features a sinusoidal wave pattern with biomimetic non-linear mechanics and controllable transitions between low- and high-stiffness behaviours, enabling tailoring to individual biomechanical functional requirements by adjusting wave design parameters. 3D printed using liquid crystal polymer (LCP), the brace harnesses the superior mechanical performance and high stiffness-to-weight ratio of 3D-printed LCP wavy fibres, given the high degree of molecular alignment achieved along the printing direction. Such that this design allows the brace to remain flexible during normal ankle inversion movements but stiffen rapidly under large strains to protect against ankle sprain injuries. Its effectiveness is examined in the gait lab, showing that the 3D-printed LCP brace provides protection comparable to commercial braces against sudden ankle inversions while not restricting natural ankle movements during walking. This makes it a potentially promising option for individuals seeking improved comfort and mobility for daily and sports activities, alongside effective sprain protection. Subsequently, the proposed ankle brace design and fabrication workflow is extended to develop a novel dynamic ankle brace for foot-drop patients in Ethiopia, offering a lighter, more comfortable alternative to traditional AFOs that can be fabricated more rapidly and cost-effectively. This makes it a feasible, affordable solution for widespread adoption in the region. Meanwhile, the use of LCP sinusoidal wave fibres in brace design could permit more natural ankle plantarflexion during gait to promote more stable and energy-efficient walking while effectively assisting with ankle dorsiflexion during the swing phase to prevent toe-dragging and reducing tripping and falling risks. Furthermore, the thesis introduces a simple and practical approach for generating non-planar toolpaths that enable the conformal printing of 3D structures directly onto freeform surfaces, especially the patient-specific anatomical structures obtained from 3D scanning, using an accessible, standard three-axis 3D printer. This opens up opportunities for the widespread fabrication of user form-fitting wearable medical devices with further improved wearing comfort and functionality. Overall, the research presented in this thesis lays the groundwork for a more general design and manufacturing workflow that enables the rapid, cost-effective, and local fabrication of patient-bespoke, lightweight, comfortable, yet effective braces for a variety of musculoskeletal conditions, such as various joint sprains and muscle pains. This workflow could also significantly improve the availability of orthotic devices, especially in developing countries, eventually improving the quality of life for patients worldwide.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2024

Author dc:creator

• Ji, Zehao

Advisor dc:contributor.advisor

• Pattinson, Sebastian

• 3D Printing
• Additive Manufacturing
• Conformal Printing
• Liquid Crystal
• Medical Devices
• Orthoses

Licence

• https://www.repository.cam.ac.uk/bitstreams/a92c186c-694a-475c-b533-cd2f7b002cee/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.112934

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/375157