What are heart stents made of?

Coronary Stent Materials

Coronary stents are primarily made of metal alloys, with bare-metal stents composed of stainless steel or cobalt-chromium alloys, while drug-eluting stents use these same metal scaffolds coated with antiproliferative drugs delivered via polymer systems. 1

Bare-Metal Stent (BMS) Materials

Stainless Steel (316L)

• The original and most widely used material for first-generation coronary stents 1, 2
• Composed of chromium-nickel-molybdenum steel (CrNiMo) alloy that provides strength, ductility, corrosion resistance, and acceptable biocompatibility 2, 3
• Contains nickel, which has allergenic potential in some patients 3

Cobalt-Chromium Alloys

• Second-generation BMS material offering improved radial strength 1
• Allows for thinner strut design while maintaining mechanical properties 1
• The Edwards SAPIEN XT transcatheter valve uses cobalt-chromium frames for enhanced circularity and radial strength 1

Alternative Materials Under Investigation

• High-nitrogen austenitic CrMnMoN steels (nickel-free) show comparable or superior strength, ductility, and biocompatibility to 316L stainless steel 3
• Nitinol (nickel-titanium alloy) causes fewer MRI artifacts and is used in some stent applications 1
• Elgiloy (cobalt-chromium-nickel alloy) is another option but may cause more imaging artifacts 1

Drug-Eluting Stent (DES) Materials

Metal Scaffold Components

• DES use the same metallic platforms as BMS (stainless steel or cobalt-chromium) 1
• The metal scaffold provides mechanical support to prevent vessel recoil and negative remodeling 1

Drug-Polymer Coating Systems

• Four FDA-approved DES types in the United States: sirolimus-eluting, paclitaxel-eluting, zotarolimus-eluting, and everolimus-eluting stents 1
• Drugs are affixed to the metal stent via polymer coatings that allow sustained drug release over time 1
• The polymer serves as a reservoir for controlled elution of antiproliferative agents 1

Bioabsorbable Polymer Options

• Newer DES incorporate bioabsorbable polymers with antiproliferative drug coatings 1
• These eliminate long-term polymer presence while maintaining drug delivery 1

Bioresorbable Stent Materials

Magnesium-Based Alloys

• Second-generation bioresorbable metal stents that completely degrade over time 4
• Some magnesium-based stents have obtained regulatory approval with mixed clinical outcomes 4
• Major limitations include excessively rapid degradation rates and late restenosis 4
• Show reduced platelet adhesion and thrombus activation compared to stainless steel 5

Zinc-Based Alloys

• Third-generation bioresorbable metal stents with more suitable degradation rates than magnesium 4
• Demonstrate better biocompatibility and more appropriate degradation kinetics 4
• Represent a promising future direction for stent materials 4

Transcatheter Valve Stent Materials

Aortic Valve Replacement Stents

• Edwards SAPIEN valve uses cylindrical stainless steel balloon-expandable stents 1
• Edwards SAPIEN XT uses cobalt-chromium frames for improved radial strength with thinner profiles 1
• Both incorporate bovine pericardial tissue mounted within the metal frame 1

Material Selection Considerations

Mechanical Properties

• Metal alloys must provide adequate radial strength to prevent vessel recoil 1
• Strut thickness affects deliverability and vessel injury—thinner struts reduce trauma 1
• Material must withstand crimping and expansion without fracture 3

Biocompatibility Factors

• Different metallic alloys have varying impacts on neointimal formation and restenosis 2
• Surface characteristics determine thrombogenicity and inflammatory response 5
• Nickel content raises concerns about allergenic potential in susceptible patients 6, 3

Radiopacity Requirements

• Adequate fluoroscopic visibility is essential for precise stent placement 4
• Tantalum and other dense metals provide superior radiopacity but are expensive 2, 7

Critical Clinical Implications

Thrombosis Risk by Material

• All metallic stents carry thrombosis risk, with BMS requiring 30 days of dual antiplatelet therapy (DAPT) 1
• DES require prolonged DAPT (minimum 6-12 months) due to delayed endothelialization from antiproliferative drugs 1, 8
• Premature DAPT discontinuation increases stent thrombosis risk catastrophically (hazard ratio 161 for subacute thrombosis) 8

Material-Specific Complications

• Stainless steel and cobalt-chromium show higher platelet adhesion than semiconductor materials like amorphous silicon carbide 5
• Magnesium alloy surfaces demonstrate markedly lower platelet adhesion and thrombus activation 5
• Very late stent thrombosis with DES may result from delayed hypersensitivity to the drug-polymer-device combination 8