• Stainless Steel – early days, not used anymore
• Tungsten – outdated
• Polymer – outdated
• Platinum – main material used for modern coils
• Inconel – only one coil on the market for peripheral use (MReye, Cook)

Why platinum (92% Platinum, 8% Tungsten)

• It is highly radiopaque, biocompatible, flexible, malleable with minimal MRI or CT artifact.
• The primary structure is defined by the raw wire, the secondary structure by the coil diameter, and the tertiary structure by the 3D overall shape.
• Volume and stiffness can vary independently according to the raw wire structure, which explains why two coils with the same diameter may deploy differently.
• Small differences in the material will induce differences in softness, pushability, packability, and radial force.

Fibered Coils

• They are coils enlaced with fibers to promote biological response and support mechanical occlusion.
• Fibers reduce occlusion time, enhancing the mechanical action of bare coils.
• Fibers enhance thrombogenicity.
• They include Concerto, Interlock, Embold, Retracta, Flipper, Nester, Tornado and MReye.

Hydrogel Coating

•  In contact with blood, hydrogen ions are released and water molecules form with the polymer causing it to expand.
• It is biologically inert and does not contain or produce biologics.
• Hydrogels are porous and compliant and allow natural tissue proliferation promoting endothelial formation.
• They do not rely on thrombus formation and can be used in coagulopathic patients.
• Azur HydroCoils systems expand 4-5 times when deployed.

Manufacturing Process

• Coil systems include a delivery wire, a wire / coil connection and a coil.
• Pusher wires are made of Stainless Steel or Nitinol.
• The connection has to be predictable, durable, visible, and easy to use.
• Occlusion characteristics depend on the thrombogenicity and the packability of the coil.

• Coil manufacturing goes back to the 70’s.
• It initially started with the idea of mechanical obstruction.
• The goal of newer coils is also to minimize recanalization.
• Animal models show that vessels occluded by fibered coils contained 70% of thrombus with fibered coils and 40% with hydrogel-coated coils.
• Long-term recanalization may be lower if it is less reliant on thrombus-related occlusion.
• We must keep in mind thrombus resorption when coiling.
• Oversizing is important in venous coiling (>50%).

 Measuring the Packing Density

• The goal is to have optimal cross-sectional occlusion to avoid recanalization.
• Initial aneurysm studies showed a minimal density of 20% to achieve occlusion.
• There is low level of evidence for a threshold.
• Coil compaction may be responsible for revascularization.

• “As much as you can safely deploy”

• Prime the microcatheter: copious flushing prior to coil insertion.
• Secure the microcatheter and keep an eye on the diagnostic catheter.
• Avoid pushing wire into the coil pack.
• “One more coil”? If hesitant, wait and perform an angio. Occlusion may be delayed.
• Remove the pusher wire with care under scopic view.
• Remove the microcatheter with care when in contact with the packing.