Assist-Knee: Energy Harvesting for Sit-to-Stand-to-Sit Transitions - PROJECT SUMMARY
This SBIR Phase II project will create and evaluate a novel low-tech Energy-Harvesting Knee Prosthesis, or
Assist-Knee Prosthesis, capable of helping geriatric individuals with transfemoral limb loss more effectively
and safely perform sit-to-stand-to-sit transitions. Transitioning from a sitting to a standing position is much
more difficult for an individual with transfemoral limb loss, especially within the geriatric population, due to
declining or absent knee and ankle musculature. When rising from a chair, these individuals heavily rely on
their contralateral limb and upper limb strength to lift their body weight. Geriatric prosthesis users, who often
have marginal and declining strength, could retain their independence if a prosthetic knee was capable of
assisting with sit-to-stand-to-sit transitions. Unfortunately, the current designs of most commercially available
prosthetic knees do not assist with the sit-to-stand-to-sit transition, a task that is fundamental for normal
activities of daily living. The Assist-Knee design harvests the prosthesis user’s potential energy during the
stand-to-sit transition and appropriately returns that energy to assist with the sit-to-stand transition. While
harvesting energy, Assist-Knee provides a resistive knee extension moment that imitates eccentric contraction
of the quadriceps muscles for a controlled stand-to-sit. The return of energy provides knee extension, imitating
concentric activity of the quadriceps muscles, for an assisted sit-to-stand. The technological innovation of this
design does not require a large motor, battery, or complex system to provide external power for knee extension
assist. Our low-cost, lightweight design is an alternative to externally powered prosthetic devices. Since
external power is not being added to the system, Assist-Knee is not intended to replicate maximum moment
output at the knee but to provide a useful fraction of knee extension moment to assist with initiation of the sit-
to-stand transition. The specific aims of this project involve: updating and optimizing the Assist-Knee design
based on our successful Phase I findings and with a user-centered design approach that includes biannual
meetings with stakeholders, and validating Assist-Knee in daily use with a laboratory and at-home clinical trial.
Successful design and implementation of Assist-Knee will enable geriatric individuals with transfemoral limb
loss to more easily complete sit-to-stand-to-sit transitions, increase independence by reducing the need for
caretaker assistance, and help control the lowering of a user during the stand-to-sit maneuver. The commercial
application of Assist-Knee is a low-cost, lightweight prosthetic alternative to assist individuals with transfemoral
limb loss within the geriatric population to independently complete activities of daily living.
