A new alloy developed by a team of researchers, including metallurgists at the U.S. Department of Energy’s National Energy Technology Laboratory (NETL), is helping cardiologists and their patients at home and abroad. The novel platinum-chromium (PtCr) alloy is being used by Boston Scientific Corporation (Natick, Mass.) to manufacture coronary stents that are more flexible and conformable than existing stents, and more visible on x-ray. The result: easier placement by the doctor and more safety for the patient.
A coronary stent is a small, expandable mesh tube that is placed in a narrowed or weakened coronary artery, allowing the passageway to stay open. Every year coronary stents save thousands of lives by expanding diseased arteries and allowing blood to flow freely.
A stent is typically inserted into an opening in the artery near the patient’s groin, and gently maneuvered through the artery until it reaches the site where blood flow is restricted. Once in place, a balloon inside the tubular metal cage is inflated to expand the diameter of the stent, opening the restricted artery and providing mechanical support to damaged arterial walls.
For decades, 316L stainless steel has been used successfully in a variety of commercially available and medically approved coronary stents. The trend in new stent designs has been to reduce stent thickness, so that the stent delivery catheter, with the stent on it, is more flexible. This allows the stent to be passed through more tortuous arterial paths, thereby facilitating treatment to obstructions that were previously untreatable by minimally invasive procedures.
But there was a catch. As the thickness of stent walls decreased, traditional 316L stainless steel became more difficult to see on x-ray. This made it difficult for the doctor, who must place the stent in precisely the right location in the artery, to see what he or she was doing—especially when the doctor needed to insert multiple stents next to each other in a single, extended location, or go back to further expand or adjust the position of a stent after implantation.
Enter NETL. More than 10 years ago, scientists at Boston Scientific called their colleagues at NETL wanting to know if the laboratory could help with research to improve coronary stents. Boston Scientific recognized NETL’s metallurgy capabilities and offered to fund the entire research project. Over the next decade, NETL and Boston Scientific worked together to design the PtCr alloy and develop the process methodology to produce the alloy for use as stent material.
The PtCr alloy solves many of the past problems surrounding traditional stents. The addition of platinum gives a stent physical properties that allow it to be both thin and visible on x-ray. Its flexibility allows easier movement through arterial bends without causing damage. The addition of high-melting platinum also gives the stent a higher corrosion resistance, which optimizes the stent’s long term stability within the body. The alloy’s increased strength also decreases recoil, which reduces the likelihood of constriction after deployment.
Following a series of trials—melting, casting, fabricating, and characterizing the properties of different alloys—and after many clinical trials, Boston Scientific’s PROMUS ELEMENT and ION stents, made from the novel PtCr alloy, were ready to market. Since introduction of the improved coronary stents in January 2010, sales have exceeded $1 billion. The breakthrough was recognized by R&D Magazine, which named the PtCr alloy one of the 100 most technologically significant products to enter the marketplace in the past year.
NETL’s materials sciences research team has done a wide variety of work in high-temperature alloy development and processing. NETL’s materials research includes making more effective armor for the Army, new turbine alloys to help the Nation’s power systems operate more efficiently, and now a medical alloy that helps save lives.
