Magneto-Rheologic Fluids and Prosthetic Applications
Dave Carlson, PhD from the Lord Corporation introduced the concept of magneto-rheologic fluids to this audience and speculated about possible prosthetic applications. Although the Chinese have been investigating the use of this technology to control a prosthetic knee for a number of years, so far there are no commercial applications in our field. But, this technology is well accepted in other industries including the automotive realm.
One of the major markets for the Lord Corporation is in MR shock absorbers. For example, they can be used to suspend the high tech driver's seat in expensive long-haul tractor-trailer trucks. Dr. Carlson explained that microprocessor control of these hydraulic pistons results in much better damping of road shock than in purely mechanical versions.
In the simplest sense, MR fluid is oil with suspended metallic particles. When a local magnetic field is created, the MR fluid thickens and flows more slowly. In one design, the fluid normally flows freely through a small orifice from one chamber to another. Applying an electromagnetic field to the orifice makes it act like a valve, restricting the flow of the fluid. Apparently MR fluid can thicken and thin out more quickly than a mechanical valve can open and close to change the resistance in a conventional hydraulic piston. This more rapid response has advantages for some applications.
Dr. Carlson showed a short video clip of a prototype prosthetic knee being developed by Bidermann in Germany that uses a Lord MR piston within an aluminum frame, in lieu of a conventional hydraulic unit. [More information and a photo of this knee can be found in the Prosthetic Knees article later in this corner.]
