Polymeric Stent Covers: Medical Coverings for Stents and Medical Devices

Many medical applications require covers to achieve various clinical outcomes, such as preventing leaks, managing tissue ingrowth, restricting tissue growth, and controlling blood flow. Polymeric stent covers can be either porous or impermeable. The type of cover depends on the chosen biocompatible polymer and covering technology. Biocompatibility refers to the ability of a material to perform with an appropriate host response in a specific application. It is determined by the final device and not only by the material used. Factors such as the implant site, duration, and intended use must also be

Choosing the Right Biocompatible Polymers for Polymeric Stent Covers

At Medibrane, we use polymers that have been clinically tested and have a long history in the medical device industry. These include medical-grade silicone, Dacron, ePTFE, and various thermoplastic polyurethanes (TPU). The choice of polymer impacts the key parameters of the cover, including thickness, radial strength, crimping profile, and whether the cover is porous or non-porous. Our engineers have extensive experience with dipping, spraying, and lamination technologies. They can help you select the best polymer and technology based on your product’s cover specifications.

Medibrane’s Unique Adhesion Platform

Medibrane’s engineers use our unique adhesion platform to improve adhesion forces. The first step involves surface activation, which prepares the metal surface for bonding with the polymeric material. This process alters the chemistry of the metal surface, improving the mechanical attachment between the cover and the stent. Next, we apply an encapsulation coating. This coating surrounds the stent’s struts, forming a closed-loop that resembles a suturing technique. The polymer cover is then applied to this closed-loop, creating a strong bond.

Impermeable, Non-Porous Covers

Stents are covered with impermeable, non-porous covers to restrict tissue ingrowth, prevent leaks, redirect fluids, and enable fluid passage. Silicone and polyurethane are the most commonly used polymers to create these covers. The polymer is dissolved and applied to the metal frame using dipping or spraying technologies. These processes are popular because they offer fast, repetitive, and cost-effective manufacturing. Polyurethanes can also be used in lamination technology, where TPU is dissolved in solution and molded into a membrane. This membrane is then laminated with heat and pressure onto the stent. Lamination with just one thin layer reduces the cover thickness and crimping profile. These technologies are well-suited for a variety of geometries, offering high accuracy and low cover thickness. They meet the requirements of many medical stents, including neurovascular stent grafts, clot retrievals, ureteral stent grafts, and gastrointestinal stent grafts.

Porous Covers for Tissue Ingrowth

Porous covers enable tissue ingrowth, prevent migration, and redirect fluids. Dacron and ePTFE are commonly used for porous stent covers. These polymers are applied to the metal frame using suturing or lamination techniques. Historically, fabrics were sutured, as lamination of a single layer without surface activation could cause delamination. Two-layer lamination with fabric would result in a thick cover with a high crimping profile, which could completely constrain the stent. Suturing is manual, time-consuming, and harder to scale compared to automated processes. While suturing creates a single layer, the sutures themselves generate a “mini-layer” and stress at the suture points, which affects the crimping profile.