The uses for silicone polymer in short- and long-term medical devices have grown over the past few decades. Medical-grade silicones are silicones that underwent biocompatibility testing. Biocompatibility is defined as “the ability of a material to perform with an appropriate host response in a specific application” (Williams, 2008). Biocompatibility is tested and determined by the final device together with its composting materials, and thus, the implant site, duration, and intended use should be considered.
Silicones are polymers, also called polymerized siloxanes or polysiloxanes, consist of an inorganic silicon-oxygen backbone chain with organic side groups attached to the silicon atoms. Silicones can be synthesized with a wide range of compositions and properties. They vary from liquid trough gel or rubber to hard plastic. Silicones are typically heat-resistant, have low chemical reactivity, are adhesive, lubricious, durable, can repel water and thus form watertight seals, and do not support microbiological growth. These qualities make them ideal for non-vascular implantable devices used in gastroenterology, urology, pulmonology, etc.
Dip and Spray Covering Technologies
To restrict tissue ingrowth, redirect fluids and enable fluid passage, stents are covered with non-porous, impermeable covers. Silicone and Polyurethane are the most used polymers to generate such non-porous stent covers. The polymer is dissolved and then applied onto the scaffold using dipping or spraying technologies. Dip coating is a very common technology due to the ability to scale up to a fast and cost-effective manufacturing process. Spray coating uses a nozzle that breaks the polymer into tiny droplets that deposit onto a horizontal revolving mandrel connected to a stent. This process eliminates gravitational forces and increases the vertical uniformity of the cover’s thickness. This technology is often used with longer stents or hypo tubes requiring thickness uniformity. Both dip and spray covering enables the development of non-porous covers with very low cover thickness (wall thickness of 15-100 µm) and high thickness homogeneity for a vast variety of stent geometries.
Silicone Covering Technologies;
Silicone Covering Is Suitable For:
Gastrointestinal stent grafts
Urological stent grafts
Neurological stent grafts
Intra bronchial valve
Wall thickness range: 15-100 µm
Coating Tolerance: ± 15% of nominal thickness
Coating weight tolerance: ± 15% of nominal weight