Introduction to Stents and Scaffold-Based Medical Applications
Stents and scaffold-based devices play a key role in treating a range of medical conditions, including those in cardiology, gastroenterology, urology, and pulmonology. These devices often require protective covers for specific purposes. For instance, covers help seal, redirect fluids, prevent migration, and safeguard surrounding tissues from damage.
Types of Covers for Stents
The materials used to cover stents can be either porous or non-porous. The choice depends on the stent’s function, the target tissue, and the duration of device usage. For example, porous covers support tissue ingrowth, while non-porous covers are more effective for sealing or fluid redirection.
Shift Towards Minimally Invasive Procedures
In recent years, the medical field has shifted toward minimally invasive procedures. This trend often involves the use of self-expandable and balloon-expandable stents, which has significantly impacted the materials and technologies used in stent covers. A key challenge in this area is crimping stent grafts to fit into narrow delivery systems. As a result, factors such as crimping force and loading force are critical in the design process.
Polyurethane: A Versatile Solution
Polyurethane is a copolymer created by reacting polyols with diisocyanates. This material is highly versatile and can be engineered to offer important properties such as biocompatibility and hemocompatibility. Additionally, it is durable, elastic, and resistant to abrasion, making it an ideal choice for medical device coatings. Given its excellent performance, polyurethane has long been a trusted material in the medical device industry.
Thermoplastic Polyurethanes (TPUs)
Thermoplastic polyurethanes (TPUs) belong to the thermoplastic elastomer family. These materials provide high strength, elasticity, and resistance to abrasion, making them particularly useful for stent covers. Manufacturers typically dissolve TPUs in a solvent, and then apply them to stents using either dip or spray coating techniques. Both methods create impermeable covers with a thin, uniform thickness.
Dip and Spray Coating Technologies
Dip coating is a well-established method for applying thin, consistent covers. On the other hand, spray coating uses a nozzle to atomize the polymer into fine droplets, which are then deposited onto the stent. This process eliminates gravitational forces, resulting in a more uniform coating. In both methods, the goal is to create impermeable covers with a thickness range of 15-100 µm.
TPU Lamination Technology
Medibrane’s engineers have developed TPU lamination techniques that allow for the creation of thin, precise covers for complex stent geometries. In this method, TPU is dissolved into a solution, molded into a tube, and then laminated onto the stent using heat and pressure. This technique enables selective covering and helps minimize the crimping profile, making it ideal for applications that require ultra-thin covers.
Porous TPU Stent Covers
In some cases, Medibrane can laser-drill holes into TPU covers, creating a porous structure that promotes tissue ingrowth. This feature improves clinical outcomes by preventing migration, which is particularly beneficial for stent grafts that require a thin, porous cover.
