The unique properties of shape-memory alloys such as nitinol have lent themselves to a variety of applications across numerous industries, including medical devices. These common shape-memory alloys, however, typically require a thermal influence to induce shape change. Straying from the norm, materials supplier Goodfellow Corp. has unveiled a shape-memory alloy that responds to magnetic fields as well as to temperature, which could pave the way for novel medical applications.
|A shape-memory alloy from Goodfellow changes shape in response to magnetic fields.|
Engineered from 50% nickel, 28% manganese, and 22% gallium, the magnetic shape-memory alloy is grown as a single crystal and then cut to shape, according to Martyn Lewis, group business development manager for Goodfellow. Capable of converting magnetic field energy into kinetic energy, the alloy can grow up to 6% in one direction when exposed to a magnetic field. It can then return to its original shape when the magnetic field is rotated by 90º.
Although Goodfellow’s magnetic shape-memory alloy is comparable to piezo-based and magnetostrictive materials in terms of functionality, it yields significantly higher strain outputs and energy densities, according to the company. “Piezo-based materials work by applying an electric current, so they won’t be generating a great deal of heat,” Lewis explains. “They do react more quickly, but the amount of movement you can get from a piezo is between 10 and 100 times smaller than the magnetic shape-memory alloy. You can get far more movement from an equivalent-sized magnetic shape-memory alloy than you could from a piezo-based material.” The magnetic shape-memory alloy, Lewis adds, has also demonstrated a faster and more efficient response rate than shape-memory alloys requiring a thermal mechanism to induce shape change.
While the material is not biocompatible, it does show promise for nonimplantable medical applications. Goodfellow has been approached by a company exploring the use of the alloy in bone stretching procedures, for instance. “If someone has a deformed jaw, you can somehow attach the material,” Lewis explains. “By applying a magnetic current, you can then slowly, and in a controlled manner, extend the bones. That’s where a thermal alloy wouldn’t work; the human body is at a constant temperature, so you wouldn’t be able to heat it up and cool it down in that application.”
Lewis proposes that the magnetic shape-memory alloy could also someday provide sensing capabilities in prosthetics. “We’re open to companies coming up with ideas, and we’ll see if [the alloy] can fit the application,” Lewis says. “The [engineers] are the ones with the ideas; we’re the guys that do the materials. Put the two of us together and we can go places.”
Published in MPMN, September 2011, Volume 27, No. 7
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