Improving Patient Outcomes with Parylene-Coated Stents

Coronary and neurovascular stents are tubular medical implants that act as a supportive framework, enhancing vascular structure. They are utilized to unblock or widen arteries, aiming to increase blood flow and lower the risk of cardiac events like heart attacks. Parylene conformal coating provides critical function to these support structures.

Parylene’s use on stents has revolutionized the efficacy and capabilities of these life-changing medical implants. The novel conformal coating not only facilitates a smooth delivery of the medical device to its destination, it also provides a valuable vehicle for drug delivery.

The Parylene Deposition Process

In contrast to other conformal coatings that are brushed, dipped, or sprayed onto a substrate, Parylene is applied via a vapor deposition process (VDP) in a vacuum chamber. During VDP, the material begins as dimer, a solid powder material. It is subjected to high heat and, in turn, transforms into a gaseous monomer without an intermediate liquid stage. This gas is then deposited one molecule at a time onto the desired substrate in the coating chamber at ambient temperatures.

This unique vapor-deposition method allows Parylene to adequately penetrate and coat extremely small stent features. In addition, this process enables the uniform and consistent coating of the complex geometries that characterize the life-saving devices. Deposited in a micron-level thickness, Parylene is also pinhole-free and can fully coat inside crevices and contours as small as 0.001 mm.

Is Parylene Safe for Stents?

Parylene is an ideal conformal coating choice for implantable stents because it is extremely inert when inside the human body. It meets the ISO 10993 and USP Class VI standards and conforms to regulatory requirements such as RoHS, REACH, California Prop65, etc. In addition to being inert and hydrophobic, Parylene offers dry-film lubricity, which is particularly advantageous during device delivery and implantation. It has significant benefits relative to Teflon™  or PTFE, including a low coefficient of friction and a lack of toxic outgassing. Parylene is also clear, while Teflon is either milky or grainy in appearance.

Parylene use in stents serves multiple functions, ultimately helping to facilitate a smooth delivery while reducing irritation and inflammation.

Parylene Use in Drug-Eluting Stents

Despite the overall success of early stents, a sizable number of patients experienced restenosis, or the re-narrowing of arteries. And while coating stents with therapeutic agents was identified as a solution to this dangerous phenomenon, the solution brought its own technological challenges in terms of bonding drugs to the stent structure and controlling drug release.

Parylene use in stents has been key to overcoming these challenges, however, and making today’s highly effective drug-eluting stents possible. First, stents were coated with Parylene to give them a surface onto which drugs such as Sirolimus could be applied. Some stents even use a series of multiple layers of drugs and polymer layers for better long-term effectiveness. In biabsorbable stent technology, thin Parylene layers are used to modulate the dissolution rate of the bioabsorbable lattice material, allowing the stent to survive to target durations. Tailoring the thickness of Parylene allows the development of platforms with varying bioabsorption rates.

As in other medical devices, Parylene’s use in stents improves their effectiveness and, more importantly, patient outcomes. The conformal coating can be accurately deposited on any commonly used stent material and can serve both as a carrier for drug delivery as well as a mechanism for controlled release and/or controlled dissolution. Its capabilities in stents point to opportunities to create additional Parylene-based drug-eluting technologies in the future.