On Feb. 8, Dr. Tom Duerig, one of the most successful entrepreneurs in the biomedical device industry, gave a seminar entitled “The History and Future of Shape Memory Alloys.”
Shape memory alloys (SMA) are materials that return to their original shape when heated. During the seminar, Dr. Duerig took a straight rod, cooled it in liquid nitrogen and bent it. When he then held the deformed rod, the heat from his hand caused the rod to quickly straighten and return to its original shape.
Most commonly, SMA consist of copper, aluminum, and nickel or nickel and titanium. Ni-Ti alloys are commonly known as “nitinol,” and were the focus of the seminar.
Originally, little was known about nitinol. Some magicians used it in their acts to create the illusion that they could bend metal with their minds. In 1972, Scientific American gave the public their first popular introduction to SMA.
The first practical application of the material started in 1975, when nitinol began being used for joining pipes. Hollow nitinol tubes could be sent through a pipe, expanding at the desired location to join two sections.
Dr. Duerig worked on the development of many different nitinol products, but none were as successful as hoped. Nitinol was sensitive to temperature changes and expensive, which made it difficult to find its optimal use.
“We realized that we needed to get in an industry that had a small temperature range and could afford the materials,” Dr. Duerig explained. When a German doctor visited, he saw the pipe products that Dr. Duerig had developed. These large hollow cylinders used for gas or water lines could be put to a different use. The doctor asked Duerig if he could make the same product, but with a 1mm diameter.
From there, Dr. Duerig developed the nitinol stent. A stent is a mesh tube used to treat narrow or weakened arteries. The medical industry was the perfect fit for the use of nitinol. The human body stays at a relatively constant temperature, and the industry can afford the expense of the material.
Today, Dr. Duerig is the Chief Technical Officer of Confluent Medical Technologies, the leading supplier of nitinol materials for the medical device industry. Nitinol research and product development is an ongoing endeavor. For example, a newer use of nitinol is found in the automotive industry.
“It turns out that nitinol has about the same compliance as human bone,” Duerig stated. For this reason, companies have started to use nitinol as the rib cages in crash test dummies for automotive testing.
Already, nitinol has been used in the industrial, automotive, and medical device industries. As Dr. Duerig and others continue to research nitinol, its practical applications will expand. By looking back at the history of nitinol, it is clear that the unique properties of shape memory alloys make them a material with the potential to reshape entire industries.
