DuPont Engineering Design Electronic Magazine
A step ahead
By Dan Curran-Blaney, DuPont Engineering Polymers, Canada
The Niagara Foot is a new, affordable, high-performance prosthetic foot intended for active individuals who have been victims of landmines. Its novel, energy-return design relies on the stiff, yet flexible properties of DuPont™ Hytrel® thermoplastic polyester elastomer to provide user benefits in terms of stability, effectiveness and comfort.
The Niagara Foot was developed by Rob Gabourie, certified prosthetist and orthotist, and founder of Niagara Prosthetic & Orthotics International Ltd. (Ontario, Canada), with support from industry partners Hippo Design (Montebello, Québec), Précicad (Québec City, Québec), DuPont (USA & Canada) and a team of engineers from Queen’s University (Kingston, Ontario).
A key aspect of its design lies in its keel – a single, S-shaped part, injection-molded from Hytrel® 8238, which acts like a spring to provide energy storage and return during the gait cycle. “The energy-return principle incorporated into the design of the Niagara Foot allows the user to walk more naturally than conventional designs,” explains Rob Gabourie. “Patients are able to detect and appreciate the performance of this device, which decreases the muscular effort required for walking.”
The combination of low flex fatigue and high stress resistance provided by Hytrel® was fundamental to achieving this concept – indeed Rob Gabourie is convinced that his design will not work with any other material. During static testing, whereby a force is applied to the toe and the heel of the foot and held for a period of time, the Niagara Foot exceeded the 3220 Newton (N) required for heel loading and 2790 N required for toe loading. A number of other materials, including polyoxymethylenes (POM) and polyamides, were unable to reach these milestones due to deformation or, in some cases, structural failure.
Further clarification for its exceptional performance in such a demanding application is provided by the material’s processing behavior. The geometry of the current design requires abnormally thick wall sections, yet because Hytrel® flows easily to produce a well-packed part, the occurrence of voids is eliminated.
Beyond the performance of Hytrel®, Rob Gabourie cites DuPont’s technical support, and its consistent quality of supply, as the reasons behind his choice of material supplier. “The technical back-up was incredible. DuPont’s knowledgeable and cooperative approach meant that not only did I receive comprehensive failure analysis during initial material evaluation, but also insightful material engineering advice, which made such an effective design possible.”