Most stents implanted today are built from metal alloys, with the specific alloy chosen to balance strength, flexibility, visibility on imaging, and compatibility with body tissue. Stainless steel dominated early designs, but the field has moved through several generations of materials, including cobalt-chromium, platinum-chromium, and nickel-titanium alloys, each engineered to solve specific problems the previous generation left behind. Beyond the metal skeleton, many modern stents carry polymer coatings loaded with drugs, and a growing category aims to dissolve entirely once healing is complete.
Stainless Steel and the First Generation
Stainless steel was the original stent metal and remains the reference point against which newer materials are measured. The alloy most commonly used is 316L stainless steel, a low-carbon variant containing iron, chromium, nickel, and molybdenum. Chromium gives the steel its corrosion resistance by forming a thin passive oxide layer on the surface, while nickel and molybdenum contribute to ductility and strength. These properties made 316L a natural early choice: it could be crimped onto a balloon catheter, expanded inside a blood vessel, and hold the vessel open without corroding.
The limitation of stainless steel is that engineers had to use relatively thick struts to achieve adequate radial strength, the outward push that keeps a vessel from collapsing back. Thicker struts mean more metal sitting against the vessel wall, which can slow healing and increase the chance of blood clots or tissue overgrowth. Stainless steel is also only moderately visible under X-ray, which makes precise placement trickier during the procedure. These shortcomings drove the search for stronger, thinner, more visible alternatives. Research has framed this progression as moving from first-generation stainless steel through magnesium-based and zinc-based biodegradable metals, though cobalt-chromium and platinum-chromium alloys filled the gap in between as the dominant permanent platforms.1PubMed Central. Evolution of metallic cardiovascular stent materials: A comparative study among stainless steel, magnesium and zinc
Cobalt-Chromium Alloys
Cobalt-chromium stents were developed specifically to allow thinner struts without sacrificing the mechanical support a vessel needs. The alloy is denser and stronger than 316L stainless steel, so less material can do the same job. A thinner profile means the stent sits lower against the artery wall, which can improve blood flow around the struts and reduce the stimulus for the vessel to scar over the device. Cobalt-chromium also shows up more clearly on fluoroscopy than stainless steel, giving the cardiologist a better view during deployment.
Several widely used coronary stent platforms are built on cobalt-chromium, including those that carry drug-eluting coatings. The alloy’s higher radiopacity, meaning it blocks more X-rays and appears brighter on screen, comes from the cobalt and chromium atoms being heavier than iron. Because the struts can be made thinner, the stent is also more flexible, which helps it navigate tortuous coronary arteries to reach the blockage site.
Platinum-Chromium Alloys
Platinum-chromium represents a further refinement of the thin-strut concept. The alloy was purpose-built for cardiovascular stents by adding platinum to a chromium-rich iron matrix. Platinum atoms are heavy, which gives the alloy excellent radiopacity so doctors can see the stent clearly during and after the procedure. At the same time, platinum strengthens the alloy through what metallurgists call solid-solution strengthening, with reported yield strengths around 480 MPa, high enough to support very thin strut designs.2PubMed. A platinum-chromium steel for cardiovascular stents
The combination of thin struts, high radial strength, flexibility, and visibility has made platinum-chromium a popular platform for both bare-metal and drug-eluting stents.3PubMed Central. Clinical utility of platinum chromium bare-metal stents in coronary heart disease One commercially important version uses a 33% platinum-chromium composition, which clinical experience has shown to track well through tight bends and maintain its shape after deployment.4PubMed. The platinum chromium element stent platform: from alloy, to design, to clinical practice Where cobalt-chromium improved on stainless steel mainly in strength-to-thickness ratio, platinum-chromium pushed imaging visibility further, which matters when a stent needs to be placed at a very precise location relative to a branch vessel or a previous stent.
Nitinol and Self-Expanding Stents
Nitinol is a nickel-titanium alloy with two unusual properties that set it apart from every other stent metal: shape memory and superelasticity. Shape memory means the alloy can be deformed at a low temperature and then return to a pre-set shape when warmed. Superelasticity means it can undergo large deformations, far beyond what would permanently bend stainless steel, and spring back without damage.5PubMed. Self-expanding nitinol stents: material and design considerations
These properties make nitinol ideal for self-expanding stents, which are compressed into a delivery catheter and then released at the target site, where they expand on their own to the vessel’s diameter. No balloon inflation is needed. This design is especially useful in peripheral arteries like those in the legs, the carotid artery in the neck, and certain biliary or esophageal applications, all locations where vessels are subject to bending, twisting, or external compression that would fatigue a rigid balloon-expanded stent. The superelastic behavior reduces the risk of the stent being permanently crushed if, for example, a patient crosses their legs and compresses the artery containing a femoral stent.6Materials & Design. Optimization based simulation of self-expanding Nitinol stent
One concern with nitinol is nickel content, since nickel can provoke allergic reactions or inflammatory responses in some people. Surface treatments help mitigate this. Techniques like magnetoelectropolishing alter the surface film to limit nickel ion release, improving both corrosion resistance and how well cells grow on the stent surface.7PubMed Central. Surface modification of Ni-Ti alloys for stent application after magnetoelectropolishing
How Material Choice Affects Mechanical Performance
The mechanical demands on a stent are intense. It must resist the artery’s tendency to recoil closed (radial strength), flex with the vessel’s natural movement (flexibility), and survive millions of heartbeat-driven pulsations without cracking (fatigue life). These requirements pull in different directions: a stiffer alloy resists collapse better but bends less easily, while a more flexible design may fatigue sooner under cyclic loading.
Research into stent mechanics has shown that radial collapse resistance depends heavily on the yield strength and ultimate tensile strength of the strut material, while flexibility and fatigue life are driven more by the alloy’s elastic modulus and how far it can stretch before breaking.8PubMed Central. Structural Design and Mechanical Properties of Metal Vascular Stents Fabricated via Laser Powder Bed Fusion This is why different alloys dominate different applications. Cobalt-chromium and platinum-chromium, with their high yield strengths, work well in coronary arteries where radial support is the priority and the vessel does not bend much. Nitinol, with its superelastic recovery, dominates in peripheral and non-vascular sites where the stent must survive repeated bending and compression.
Drug-Eluting Coatings and the Drugs They Carry
A bare-metal stent solves the immediate problem of a narrowed artery but introduces a new one: the vessel’s healing response can produce scar tissue that re-narrows the opening, a process called restenosis. Drug-eluting stents address this by coating the metal skeleton with a thin polymer layer loaded with a medication that suppresses cell overgrowth.
The two drugs with the longest clinical track record are sirolimus and paclitaxel. Both slow down the cell cycle that drives scar formation, but they do so at different stages. Sirolimus blocks an earlier phase, while paclitaxel interferes with a later step in cell division.9Journal of the American College of Cardiology. Sirolimus and Paclitaxel on polymer-based drug-eluting stents: similar but different Drug-eluting stents have substantially reduced the rate of restenosis compared to bare-metal stents, delivering medication directly to the vessel wall without flooding the rest of the body with the drug.10PubMed. Drug-eluting stents: preventing restenosis Newer-generation drug-eluting stents have largely moved to everolimus and zotarolimus, both relatives of sirolimus with refined release profiles.
The polymer coating itself matters. Early drug-eluting stents used durable polymers that stayed on the stent permanently, but these coatings were linked to delayed healing of the vessel lining, which raised concerns about late blood clot formation. Current designs use either bioabsorbable polymers that dissolve after the drug is delivered or polymer-free surfaces where the drug is loaded into micropores etched directly into the metal.11PubMed. Polymer-Free Drug-Eluting Stents: An Overview of Coating Strategies and Comparison with Polymer-Coated Drug-Eluting Stents Microporous stent surfaces have shown promising results as a way to control how quickly the drug releases without needing any polymer at all.12PubMed. Modelling drug release from polymer-free coronary stents with microporous surfaces
Why the Vessel Lining Matters So Much
After a stent is placed, the body’s goal is to grow a fresh layer of endothelial cells, the smooth lining that normally covers the inner surface of blood vessels, over the stent struts. Until that layer forms, exposed metal is a magnet for blood clots, which is why patients take blood-thinning medications after stent placement. Faster and more complete endothelialization means a lower risk of late thrombosis and a shorter course of those medications.
The stent material itself influences how quickly endothelial cells colonize the surface. Standard 316L stainless steel is biologically inert, which sounds like a good thing but actually means it does not actively encourage cell growth. Researchers have experimented with adding trace copper to 316L steel, finding that copper-bearing stainless steel promoted endothelial cell growth and improved the expression of genes involved in new blood vessel formation. In animal studies, copper-bearing bare-metal stents showed better endothelialization than both standard bare-metal and drug-eluting stents.13PubMed Central. Evaluation of promoting effect of a novel Cu-bearing metal stent on endothelialization process from in vitro and in vivo studies
Surface coatings are another avenue. One experimental approach immobilizes exosomes, tiny vesicles naturally secreted by cells, onto a polydopamine-coated stent surface. This coating not only increased the number of endothelial cells attaching to the material but also improved their function, including their ability to release nitric oxide, a molecule that helps keep blood vessels relaxed and clot-resistant. The same coating discouraged the attachment of inflammatory immune cells and the overgrowth of smooth muscle cells, both of which interfere with healthy healing.14PubMed. Tailoring of cardiovascular stent material surface by immobilizing exosomes for better pro-endothelialization function
Bioresorbable Stents That Disappear
The idea behind a bioresorbable stent is appealing: prop the vessel open long enough for it to heal, then dissolve harmlessly so no permanent implant remains. This would allow the artery to regain its natural flexibility and respond normally to changes in blood flow. Two broad categories are under development: polymer scaffolds and biodegradable metals.
The most studied polymer is poly-L-lactic acid, or PLLA, the same material used in absorbable surgical sutures. PLLA scaffolds gradually lose molecular weight through hydrolysis, a process where water breaks the polymer chains. Research has shown that the scaffold becomes brittle and eventually fails structurally once its molecular weight drops below a critical threshold, and this loss of ductility happens before any noticeable mass loss or change in the material’s crystalline structure.15Polymer Testing. Investigation of the degradation behaviour of poly-L-lactic acid braided stents under real-time and accelerated conditions Predicting exactly when a PLLA scaffold will lose its mechanical support requires sophisticated modeling that accounts for how the crystalline and amorphous phases of the polymer degrade at different rates.16PubMed. An integrated mechanical degradation model to explore the mechanical response of a bioresorbable polymeric scaffold One challenge with PLLA is that its breakdown produces lactic acid, which can create a locally acidic environment and provoke inflammation.17Advanced Engineering Materials. Controlled Degradation of Poly(L‐Lactic Acid)/Trimethylene Carbonate/Magnesium Hydroxide Composite Bioresorbable Stent: Synergistic Effects on Long‐Term Resorption and Mechanical Support
Biodegradable metallic stents sidestep some of PLLA’s weaknesses. Magnesium-based stents have shown positive clinical results, being fully absorbed within about 12 months and demonstrating low rates of vessel re-narrowing at follow-up. Iron-based stents take longer to dissolve, roughly three years for complete absorption, but have shown consistent vessel expansion beyond six months after placement.18PubMed. Coronary bioresorbable metallic stents: Advancements and future perspectives Magnesium stents degrade faster and produce byproducts the body handles easily, but that fast degradation means they may lose structural support before the vessel has fully remodeled. Iron stents hold up longer mechanically but must be designed so the corrosion products do not accumulate in concerning amounts. Zinc is being explored as a middle ground, with corrosion rates between those of magnesium and iron.
Stents Outside the Cardiovascular System
Stent materials are not just a cardiology story. Stents are routinely placed in bile ducts, the esophagus, ureters, airways, and other tubular structures throughout the body, and each location imposes its own material requirements. Biliary stents, for instance, must resist the corrosive effects of bile while preventing bacterial biofilm from clogging the stent channel. Plastic biliary stents made from polyethylene or polyurethane are still widely used for temporary drainage, while self-expanding metal stents, usually nitinol, are preferred when longer-term patency is needed. Both types face restenosis problems, driving interest in biodegradable polymer and metal biliary stents along with functional coatings that resist bacterial adhesion.19PubMed Central. Biliary stents for active materials and surface modification: Recent advances and future perspectives
Airway stents for treating tracheal or bronchial narrowing face yet another set of demands: they must hold a large-diameter tube open against the compressive forces of coughing and breathing while remaining flexible enough not to erode through the airway wall. Silicone stents are the classic choice in this setting because they are easy to reposition or remove, though metal mesh stents covered with silicone or polyester fabric offer stronger radial support. Ureteral stents, meanwhile, are typically made from polyurethane or silicone and are designed to be temporary, lasting weeks to months before removal or replacement.
Composite and Specialty Wire Materials
Some of the newest stent concepts use composite wires rather than a single uniform alloy. One approach combines an absorbable iron-alloy shell with one or more pure molybdenum cores, drawn down to wires as thin as 25 to 250 micrometers. These composite wires achieve mechanical properties competitive with existing permanent flow-diverter materials used in neurovascular applications, while the iron-alloy portion is designed to corrode and eventually disappear.20PubMed Central. Radiopaque FeMnN-Mo composite drawn filled tubing wires for braided absorbable neurovascular devices The molybdenum core provides radiopacity and structural reinforcement during the critical healing window, while the iron-manganese-nitrogen shell supplies the bulk mechanical strength and then degrades over time.
This composite philosophy reflects a broader trend in stent design: rather than asking one material to do everything, engineers are layering materials with complementary strengths. A thin radiopaque core for imaging, a strong but degradable shell for support, and a bioactive surface coating for healing can each be optimized independently.
MRI Compatibility and Imaging Artifacts
Patients with stents often need MRI scans at some point after implantation, and the stent material determines both safety and image quality. Most modern coronary stents are labeled MRI-conditional, meaning they can safely go through a scanner under specific conditions. However, the metal still distorts the magnetic field locally, creating artifacts that can obscure the very anatomy the scan is trying to image. The size and shape of these artifacts depend on the type of stent, its dimensions, and which MRI pulse sequence is used.21PubMed. Coronary arterial stents: safety and artifacts during MR imaging
Stainless steel stents, which contain nickel and are slightly ferromagnetic, tend to produce larger artifacts than cobalt-chromium or platinum-chromium stents. Nitinol, despite its high nickel content, is non-ferromagnetic and produces relatively small artifacts, making it one of the more MRI-friendly stent metals. For patients who are likely to need repeated MRI monitoring, such as those with cancer or neurological conditions, the choice of stent material can influence long-term imaging quality.
3D Printing and the Next Generation
Additive manufacturing is opening up possibilities that conventional stent fabrication, mainly laser-cutting tubes of metal, cannot match. Three-dimensional printing allows stent architectures to be customized for an individual patient’s anatomy, with strut patterns and thicknesses varied across the length of the device to match the vessel’s geometry.22ACS Omega. Recent Advances in 3D-Printed Bioresorbable Vascular Stents: Toward Patient-Specific, Novel-Structured, Functional, and Smart Devices Researchers have explored 3D printing with bioresorbable shape-memory polymers, which could combine the disappearing-stent concept with self-expansion, eliminating the need for balloon inflation and reducing the risk of the stent migrating after placement.23PubMed. Advancing Toward 3D Printing of Bioresorbable Shape Memory Polymer Stents
Beyond customized geometry, the field is moving toward stents that do more than just sit passively in a vessel. So-called smart stents integrate sensors small enough to fit within the stent structure, potentially monitoring blood flow, pressure, or signs of restenosis in real time and transmitting that data to a clinician. Four-dimensional printing, which adds time-dependent shape change as a design parameter, is also being explored as a way to build stents that adapt their shape after deployment. Continued miniaturization of sensor components and development of energy-harvesting metamaterials could eventually make in-body monitoring a routine part of stent therapy.24Annals of 3D Printed Medicine. The future of 3D printing in instrumented implantable polymer meta-stents