Development of Prosthetic Foot with Controlled Energy Storage and Release

Period of Performance: 09/01/2008 - 08/31/2010


Phase 2 SBIR

Recipient Firm

Intelligent Prosthetic Systems, LLC
Ann Arbor, MI 48104
Principal Investigator


DESCRIPTION (provided by applicant): The long-term goal of this project is to develop an intelligent prosthetic foot that reduces the energy consumption of walking in amputees. Commercial prostheses use passive mechanisms to provide articulation, cushioning against heel impact, and elastic energy return; yet the energetic cost of amputee walking is high. Currently the most sophisticated prostheses are intelligent knees, which improve gait by actively controlling braking of the knee. Based on recent laboratory results, we propose that controlled energy storage and release could significantly improve the efficiency of a prosthetic foot. Such a foot would store elastic energy after the foot strikes the ground, as in current products. But instead of returning energy spontaneously, active control would capture that energy with a latch mechanism, and release it later in the gait cycle, coinciding with the push-off phase of able-bodied walking. The proposed mechanism will be microprocessor-controlled, and will require battery power mainly to actuate a latch rather than to actively power gait. This low power demand means that the prosthesis will be able to operate for hours at a time using lightweight batteries. Phase II of this project will develop a prototype prosthesis, and experimentally test the conceptual feasibility of intelligently controlled energy release. We intend to develop this concept into a commercial prosthesis with greater energy return and comfort than conventional designs, in a compact and lightweight package. The proposed research has three Specific Aims: design and fabrication, testing on able-bodied subjects, and testing on transtibial (below-knee) amputees. (1.) The design component consists of developing a lightweight and compact, computer-controlled mechanism for controlling and then returning mechanical energy to the user. (2.) We will test the device on able-bodied subjects, to compare the metabolic energy that they expend during walking. Able-bodied subjects will be used to monitor the differences between the prototype device, conventional prostheses, and able-bodied walking. (3.) We will also test the device on the target population of transtibial amputees. We will provide subjects with long-term loans of the prototype device so that they can practice walking and become familiar with it. We will then compare their energy demand when walking on their own prosthesis, with a high performance conventional prosthesis, and with the prototype device. We will test whether controlled energy storage reduces the metabolic demand for walking, which serves as an objective measure of the device's efficacy. Relevance: This research addresses the public health problem of reduced mobility in lower-limb amputees using prosthetic feet. These amputees walk at lower speed, high energy cost, and with lower range and comfort than able-bodied individuals. The proposed controlled energy storage prosthetic foot is intended to provide measurable improvements in these aspects of mobility. This project seeks to reduce the energetic demand of walking in lower limb amputees, for whom walking with a prosthesis is more fatiguing than for able-bodied persons. The project will develop a prosthetic foot with an ability to efficiently store energy that is normally dissipated in conventional prostheses, and then to return that energy to power walking, in order to reduce the effort of walking for amputees.