Alloy with "Memory" Helps Fractures Heal - Nitinol - Brief Article

USA Today (Society for the Advancement of Education), Oct, 2000

A metal wire that "remembers" its shape may be ideal for helping a broken bone heal faster and more reliably. Researchers at Ohio State University, Columbus, compared Nitinol--a nickel and titanium alloy--to stainless steel in an experiment designed to see which metal worked best on a simulated broken bone. Where the stainless steel wire lost tension during the simulation, the Nitinol kept a continuous pull. Loss of tension could cause a bone to heal improperly.

"Metals like Nitinol remember their original shape," indicates Alan Litsky, associate professor of orthopedics and biomedical engineering. "This shape `memory' can be used to help compress broken bones, which could mean a quicker healing time, and a better fusion of the bone."

One common way that surgeons treat certain fractures is to tie wire around the affected bone in order to pull the fractured pieces together. The problem is that stainless steel --the most common metal used in these wires--tends to loosen over time as it slowly migrates through the bone. This reduces the amount of pressure applied to the fracture and can result in poor healing.

Nitinol, if it is stretched before being wrapped around a fractured bone, resists loosening because it remembers its original shape. This "memory" allows the wire to continue compressing the bone even after that wire starts to be absorbed by the bone.

When using Nitinol to repair a broken bone, a surgeon would flush the fracture site with water slightly cooler than body temperature, then wrap the prestretched Nitinol wire around the site of the break. After the wire warmed, it would attempt to regain its original shape, and then continuously push the bone back together.