Stents, the tubes used in surgical procedures to artificially prevent constriction of natural passageways in the body such as arteries, can be made of a variety of materials. Traditionally, metal has been the most popular type of stent material, with stainless steel being the most common; other types of metal used to make stents include cobalt-chromium, gold, and tantalum. Polymers such as silicone and polyurethane are also sometimes used, though they can have issues such as low durability or bioreactivity. While polymers may be more permanent, some others degrade relatively quickly in the body, which makes them useful for producing stents that are only needed temporarily or if medication needs to be released into the body. The use of shape memory polymers to make stents has also been explored.
Metal is frequently used as a stent material due to its strength, flexibility, and biocompatibility. Stainless steel is very popular for making stents, as it is quite cost effective. Interestingly, it is not ideal from a biocompatibility standpoint, as it can often cause restenosis and thrombosis, both which can restrict blood flow, after being implanted in heart patients. Other alternatives have shown greater promise in decreasing the likelihood of a negative physical reaction to stenting. Both gold and cobalt-chromium have proven to be effective and biocompatible stent materials, though gold can be quite expensive. Tanatalum and nitinol are also promising, though the first can be somewhat brittle and the second difficult to manufacture.
The other main type of stent material is polymers. Silicone is well-tolerated by the body, but it is not ideal when it comes to strength and durability. Polyethylene and polyurethane have the opposite problem. They are quite strong and hold up well within the body, but biological materials tend to adhere to them and sludge can build up within them.
Polymers that are biodegradable, bioabsorbable, or bioerodible can offer certain advantages when used as stent material. They can be used when a stent is only needed temporarily and will not need to be removed later. Drugs can be imbedded in the material so they are released over time as the stent degrades. One disadvantage to using them is that their surfaces become uneven as they erode, which may lead to biological material adhesion.
Shape memory polymers are another potential stent material. These substances can be created in a temporary state and then later transitioned to a more permanent shape using heat or cold. This may help form stents that are ideal for the specific location they are needed.