Embolization Coiling: The importance of material selection

Embolization coiling is a minimally invasive catheter-based procedure that employs a coil that can cause an occlusion. This occlusion prevents bleeding at the site of a weakened blood vessel that has ruptured (or is about to rupture). To design such a catheter, the product designer needs to have a strong understanding of bio-material capabilities and must keep in mind elements such as flexibility, lubricity, kink resistance, push strength, torque-transfer characteristics, and more. Materials determine the functioning and outcomes. This must be effectively matched with the intended medical procedure. I.e. to treat a brain aneurysm, close a PDA, stop abnormal AVM, or stop intestinal bleeding. 

Risks & Safety Considerations with Embolization Coiling

When you evaluate the materials that can be extruded into coils, it is essential that complications associated with the catheter and coils are negligible or eliminated altogether. Risks are caused by too much coiling at the intended site or, use of a coil material that does not fix well at the intended site, or coil being too hard, or even micro-level mistakes in catheter placement. This means that the coil material should be soft and detachable from the catheter. Varying stiffness such as Ultrasoft, Soft, Standard, Firm and stretch resistant are available.  

Types of Embolization Coils

Depending on the intended function and site of application Coils can be designed as:

• Pushable 
• Injectable
• Detachable 

The shape, size and functioning of embolization coils vary significantly. Defining the size of the coil has a major impact on its risk ratio. A general rule when designing an embolization coil, is to manufacture the coil 20%-30% larger than the affected blood vessel. This ensures that the risk of distal migration is insignificant. Any larger and the coil may not form its intended shape (3D, 2D or Helical). Coil diameters can range from 0.035” (Macro-coils) to 0.01” (Micro-coils), the length of the coils can vary between 1mm to 60cm. Once the coil has been delivered, it takes a few seconds to a few minutes for the thrombus to form. Adding micro-fiber threads (made of Dacron, wool, nylon, polyesters, or PVA) to the coils helps increase its thrombogenicity.    

Design of Catheters and Types of Catheter Materials

There are a number of materials that can be used to produce catheters that deliver coils. Historically, Steel, Platinum, Titanium and Iridium have been used. To understand the design of an embolization coil catheter has a look at Figure 1 below.

Catheters may be designed as braided or coiled, offering varying degrees of flexibility – a feature that is useful for detachable coils. The braiding filaments may be made of polymers or Teflon or a combination. The precise pattern of braiding also influences the flexibility of the coil. In order to increase lubricity during navigation, the catheter can be coated with a biocompatible lacquer. 

In order to select the right mix of materials, the right questions must be asked by the product engineer: Rigidity of the proximal end, the flexibility of the distal end, how much elasticity is required, pushability required, etc.

Production of Catheter and Coil:

What’s important is that the catheter designed for embolization coiling is easy to handle and produces the desired effect at the intended location. The selection of its materials is of utmost importance since the perfect balance in tensile yield, stiffness, and catheter push ability should be achieved. Quasar’s bio-materials specialists are at your disposal, backed by cutting-edge micro-braiding, polyamide processing, and layering capabilities. Partner with us and you will reduce production risks and cut time-to-market at least by half.