Graduate Student Seminar Series – Julia Takimoto

Graduate Student Seminar Series
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Location: MS2158 – 1 King’s College Circle
Presentation Title: Quantifying the Rotational Stiffness of 3D Printed Ankle Foot Orthotics
Abstract:
Background and Rationale: Ankle-foot orthoses (AFO) are assistive devices designed to improve gait biomechanics and/or correct structural abnormalities. AFOs are commonly prescribed in a multitude of cases, including stroke, osteoarthritis, cerebral palsy, spinal cord injury, foot drop, and clubfoot. Their use has been found to improve dorsiflexion angle, gait speed, stride length, and reduce energy cost. Recent improvements to 3D printing technology have made it a commercially viable manufacturing method for custom orthoses. To 3D print an orthotic, a scan of the lower limb is taken and digitally manipulated to achieve the desired AFO characteristics. Key characteristics of AFOs are rotational stiffness and shape, affecting safety, comfort and function, which are fine-tuned during the post-processing phase of manufacturing. While it is not a common part of clinical practice, the prediction of these characteristics can be assisted using Finite Element Analysis (FEA) of the computer-aided design (CAD) models or empirical testing. Current testing methods to verify the predicted characteristics are modelled after lower-limb prosthetics, but no ISO standards for AFO testing have been established and methods presented in research are not commercially available. Furthermore, it is not feasible for many orthotic clinics to develop a custom testing machine, so this project seeks solutions that can potentially be applied in clinical practice.
Objectives and aims: The main goal of this project is to develop and assess techniques for assessing the strength and stiffness of AFOs.
To achieve this, I aim to: (1) Develop a testing apparatus and procedure to quantify the material properties and behaviour of 3D printed AFOs under static and dynamic loading conditions and determine the apparatus reliability within testing cycles and across testing sessions. This procedure will serve as a gold standard that other methods will be compared to. (2) Use said apparatus to test key aspects of AFO post-processing. (3) Develop and evaluate a low-technology, clinically-viable process for AFO stiffness testing.
Methodology: (1) A custom apparatus will be designed for attaching AFOs to mimic walking within a universal tensile machine (UTM). The apparatus will apply loading to a surrogate shank, with the AFO footplate fixed (in a non-destructive manner) to isolate motion to the ankle joint. The primary measure will be rotational stiffness in the sagittal plane, which is the key characteristic in the design and prescription of AFOs, but also a common cause of structural failure in long-term AFO use. (2) Measure the effects of heat treatment for shape modification and dyeing the AFOs and compare to FEA predictions of AFO behaviour. (3) Analyse current benchtop stiffness testing and develop a methodology optimised for clinical use, prioritising low cost and ease of use.
Significance & Contribution to Advancement of Knowledge: The rotational stiffness of custom and pre-made AFOs is typically unknown. Traditional plaster casting methods for custom AFOs rely on an orthotist to visually determine when an appropriate stiffness has been achieved, without quantification. Pre-made AFOs are sold with their stiffness on an arbitrary range from low to high. 3D printing provides the opportunity for orthotists to manufacture AFOs with specific stiffnesses; however, many orthotists are unfamiliar with prescribing a numerical stiffness value. Creating a standard quantification method enables further study of the impact of specific AFO design characteristics on users’ gaits. This leads to better AFO prescriptions and aids the development of AFO standards.
Supervisor Name: Jan Andrysek
Year of Study: 3
Program of Study: MASc
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