Originally Published November 2000

State-of-the-Art Prosthetic Leg Incorporates Magneto-Rheological Technology

Many of the innovations developed in the medical device industry find applications in other industries as well. Likewise, technology developed elsewhere, even for the most seemingly unrelated applications, often finds use in medical devices. When Biedermann Motech (Schwennigen, Germany), a manufacturer of spinal implants and prosthetic components, was seeking a way to improve stability, gait balance, and energy efficiency for amputees using its Smart Magnetix prosthetic leg, it found a solution in technology taken from a truck-seat damper.

Smart Magnetix provides fast adaptation to control knee movement, yet is robust and affordable for the amputee.

Lord Corp. (Cary, NC), a materials technology company, modified the magneto-rheological (MR) technology found in its truck-seat damper and designed it into the Smart Magnetix prosthetic leg. Its combination of MR, electronics, and software enables the device to respond 20 times faster than prior state-of-the-art designs and therefore it achieves the closest neural human reaction time of movement for the user. In other words, the newly designed prosthetic more closely mimics the process of natural thought and locomotion than previous prosthetic designs.

Magneto-rheological technology allows the prosthetic leg to closely recreate a natural gait.

Lord's MR technology is based on proprietary and patented MR fluid formulations; damper, mount, brake, and clutch designs; and sophisticated computer-control algorithms. When exposed to a magnetic field, MR materials change consistency from a fluid to a near-solid state. The materials consist of micron-sized, magnetically active particles dispersed in a carrier medium. In the presence of a magnetic field, the particles align and resist flow, leading to high forces when required to move. The materials in MR particles respond to the applied magnetic field within milliseconds, allowing for real-time control of the fluid rheology.

"Slopes and stairs have traditionally been a nightmare for an amputee," says Lutz Biedermann, president of Biedermann Motech. "But Lord's controllable material has made it possible for patients to achieve confidence in their steps. Biedermann Motech is finally able to provide a solution for stable and reliable support without noticeable differences in movement or limitations for the user."

Conventional stepper motor–powered prosthetic devices lack the same degree of stability that Biedermann Motech's battery-operated and electronically controlled MR damper knee mechanisms can provide. Biedermann Motech's Smart Magnetix system adapts to all possible movement changes in milliseconds. Lord's MR damper is designed to perform in combination with sensors and software to detect and adjust to changes in walking speed, uphill and downhill motion, high and low loads, ramps, stairs, and terrain differences. The system analyzes the patient's gait to adapt knee motion appropriately and with fine control within milliseconds.

MR technology provides infinitely variable, real-time damping control. The MR dampers are highly adjustable and instantly responsive to the changing needs of the device user. In contrast, conventional hydraulic shocks are not real-time adjustable, and controllable hydraulic shocks with stepper motors adjusting the valving provide less adjustability, speed, and control.

MR technology was invented in the 1940s, but the first fluids and devices had limited life and stability in applications such as shocks, dampers, brakes, and clutches. Without digital processing and fast, inexpensive computing, MR technology was never commercialized until Lord Corp. began developing the technology 15 years ago. Recognizing the need for flexible, less complicated control capabilities, it has gone beyond the original idea of MR technology to develop stable, wear-resistant suspensions that can withstand the rigors of primary and secondary suspension applications. The company has commercialized several applications that match the lifetime performance of more complicated and expensive controllable hydraulic and electromechanical systems.

MPMN is actively seeking success stories like this. If your company has one to share, please contact MPMN, 11444 W. Olympic Blvd., Los Angeles, CA 90064-1549, 310/445-4267, or e-mail: [email protected]

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