Metals thrombogenic

At this time all commercial vena cava filters are fabricated firan ehber nitinol (nickel, cobalt, and titanium alloy), phynox (nidcel, cobalt, chromium, iron, and molybdenum alloy), or stainless steel wire in various catfaeter sheath sizes raiigii fiom 7-14 French (23 - 4.7 mm diameter). These metals were chosen because fiiey are biostable and have low thrombogenicity. This means that blood is less likely to form clots cm the surfiice, and cells are not encouraged to grow around the device. Moreover, nitinol is a thermal shape memory alloy that is self-expanding afier deployment and exposed to txxfy temperature(l]. 

In early canine implant studies, the thrombogenicity of a wide series of metallic implants was seen to be related to the resting electrical potential of the metal which was generated upon blood contact [21]. Metals with negative potentials tend to be antithrombogenic, while stainless steel tends to be neutral. Copper, silver, and platinum are positive and extremely thrombogenic. Indeed, the use of copper coils inserted into canine arteries continues to be a widely used model for inducing a thrombotic response [22]. 

Theoretically, reduced thrombogenicity of metallic stents and heart valve components might be achieved by thin film polymer coatings, although the clinical effectiveness of this strategy has not been demonstrated. Thus, chronic systemic anticoagulation is generally employed in patients with prosthetic heart valves (with metallic components) and stents. 

However, permanent metallic implants have some drawbacks that limit their more widespread use. These limitations include long-term endothelial dysfunction, delayed re-endothelialization, thrombogenicity, permanent physical irritation, chronic inflammatory local reactions, mismatches in mechanical behavior between stented and non-stented vessel areas, inability to adapt to growth in young patients, and, importantly, non-permissive or disadvantageous characteristics for later surgical revascularization. 

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