Enhancement of Magnetorheological Fluids for Prosthetic Knee Applications

Overview

In developing knee prosthetics, actively tuning the stiffness of the knee is crucial to facilitate natural movement and decrease fatigue for the amputee. Latest devices exploit the highly tunable on-off state of magnetorheological fluids (MRFs), given their ability to rapidly change from liquid to a semi-solid state under the influence of applied magnetic fields. Nonetheless, current technologies face challenges in a) flexibility, b) support for weight/activity and c) device lifespan, due to limitations of the MRF used. This investigation tackles these challenges by enhancing the corresponding MRF properties: a) reducing off-state viscosity, b) increasing on-state yield stress and c) improving stability against sedimentation. Owing to high oleic acid content, MRFs utilising a novel base fluid of safflower oil displayed superior on-state yield stress as well as improved stability against sedimentation compared to conventional silicone oil. Addition of FeCo submicron particles (SMP) strengthened Fe columnar structures formed on-state, increasing the on-state yield stress. This also improved the suspension stability and bypassed the traditional problem of increased off-state viscosity due to greater solid loading. Coating the FeCo SMP with stearic acid largely reduced interparticle aggregation, further improving the on-state yield stress attainable. The tailoring of MRF composition in this study achieved high on-state yield stress while ensuring lower off-state viscosity, and also highlighted practical methods to reduce sedimentation. On-state yield stress to off-state viscosity ratios attained exceed conventional industry standards by more than two-fold. This study successfully optimized MRF composition for promising enhancement of prosthetic knee function.

Awards (1)

• Second Award of $2,000 $2,000

Competition history

• ISEF 2017 Materials Science · Entry MATS018T

Resources

• ISEF abstract page ↗

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