A catheter is a thin tube extruded from medical grade materials serving a broad range of functions - it can be inserted in the body to treat diseases or perform a surgical procedure. By modifying the material or adjusting the way catheters are manufactured, it is possible to tailor catheters for cardiovascular, urological, gastrointestinal, neurovascular and ophthalmic applications. The call for minimally invasive surgical techniques involve small incisions that are a conduit through which instruments and devices can be inserted to treat or clean diseased/blocked passages or vessels, or deliver medications. As per mddionline.com, vascular catheters used in minimally invasive surgery face a number of design challenges. While they must be fairly stiff at their proximal end to allow the pushing and maneuvering of the catheter as it progresses through the body, they must also be sufficiently flexible at the distal end to allow passage of the catheter tip through smaller blood vessels without causing significant trauma to the vessels themselves or to the surrounding tissue. This combination of flexibility, high tensile strength, and compression resistance is what makes designing a vascular catheter challenging. Catheters require enhanced performance properties to reach deeper inside the body.  At the same time, device manufacturers are aggressively pursuing cost reductions associated with these devices. This has lead to several new material and compound developments.

Manufacturers of catheters can benefit through increased production efficiency by eliminating a need for co-extrusion, which is typically required to manufacture striped catheters, as well as reducing material usage and complexity. NEU^TM View Radiopaque Translucent Solutions, an innovative polymer formulation that provides catheter manufacturers and healthcare professionals enhanced material functionality and performance has been launched by PolyOne Corporation. Catheters made using the patent-pending NEU View technology provide optical visibility (translucent) when outside the body and superior visibility under X-ray (radiopaque) when inside the body. This solution provides significant advantages when compared with existing striped radiopaque catheters, which offer less X-ray visibility and may require multiple manufacturing steps and materials to produce. This technology enhances the ability of clinicians to make visual confirmation of fluid flow and can allow for detection of potentially harmful air bubbles that might cause embolisms, while patients can experience greater comfort via use of a single catheter. Catheter manufacturers can now offer a commercially viable product that provides excellent visibility, both optically and under X-ray, enabling performance improvements and efficiencies in the healthcare field.

Foster Corporation, a leader in custom polymers for medical devices, has developed LoPro Plus^TM radiopaque compounds reinforced with nanoparticles for improved pushability of thin wall catheters.  These compounds allow for extrusion of single layer tubes with radiopacity and strength properties equivalent to conventional two layer tubes, in which each layer provides the distinct properties.  LoPro Plus^TM reduces material and inventory costs when compared to standard two layer constructions. Radiopaque compounds typically include 30-40% barium or bismuth filler to provide fluoroscopic visibility of catheters within blood vessels; however, these fillers are not designed to improve strength properties.  Improved pushability and torque for catheters that must reach deep in the body or precise locations often requires coextrusion of additional layers using polymers with high strength properties.  This can increase manufacturing costs due to the purchase and inventory management of multiple materials.  These compounds combine radiopacity and strength, and use particles that are less than a nanometer thick and up to 1,500 times the thickness in length. These extremely small reinforcements are dispersed throughout the polymer at the molecular level to improve physical properties.  When added to radiopaque filled compounds in small quantities, the nano particles improve rigidity without increasing brittleness. Recent studies performed by Foster indicate the addition of 3% nano particles to a 72 durometer polyether block amide (PEBA) with 35% bismuth filler, improves flexural modulus by 60% and increases elongation by 10%. These compounds are designed to replace multi-layer tubes with a single layer, which will reduce material and inventory costs. Material and processing costs can be twice that of traditional radiopaque compounds. As such, these materials are intended for precision drug delivery catheters in which both radiopacity and transparency is critical.
The company has also introduced heat and light stabilized polyether block amide (PEBA) copolymers that resist oxidation and degradation during storage. Foster HLS^TM formulations are manufactured from medical grade Pebax polymers and USP VI additives for use in medical device applications such as vascular catheters. PEBA copolymers, like many polymers, degrade due to environmental stress agents such as oxygen, moisture, heat and ultraviolet light over time. This can cause a loss in material properties and reduced functionality of medical device components that have been stored in such conditions. Foster has developed a targeted stabilizer system which can both decompose and neutralize the free radicals created by exposure to oxygen, heat and UV light, which otherwise will initiate the loss of polymer properties.  These polymer formulations can extend reliable functionality of medical devices. In two studies recently conducted by Foster, HLS 2533 MED demonstrated substantial long-term property retention compared to the non-stabilized PEBA medical grade.  Following 6 months of exposure to multi-source indoor light, HLS 2533 MED test samples retained 99% tensile strength whereas the non-stabilized PEBA samples demonstrated severe degradation and property attrition after 3 months of light exposure.  In a separate study, samples were exposed to 131°F (55°C) for 32 weeks to simulate ageing for 5 years at 77°F (25°C). The HLS stabilized samples retained 99% tensile strength compared to 78% of the non-stabilized PEBA samples.

Low-durometer polymers are often used to manufacture catheters and medical tubing because they afford flexibility to the physician who is navigating the device through the vasculature while minimizing patient trauma. However, the material's inherent friction can lead to manufacturing and packaging issues and create complications in the final application. Innovative Polymer Compounds has developed a material based on a medical-grade polyether block amide from Arkema, Pebax MED, that improves lubricity and adds functionality. As told to PlasticsToday. "We tweaked the formulation of Pebax in terms of lubricity and, to some extent, conductivity. This was achieved by adding a nano additive to the material, called PEBA Slide, that resulted in a measurable improvement in the coefficient of friction.” The additive significantly lowered the dynamic coefficient of friction on dry samples and on samples lubricated with a 40%-wt aqueous glycerol solution to mimic the viscosity of blood. A 36% reduction in coefficient of friction was achieved using material prepared with a low loading of the nano-additive per ISO 8295/ASTM 1894 test methods. By adding a hydrophilic Pebax grade, the coefficient of friction was reduced even further to 55% below the virgin resin. The improvement in coefficient of friction was observed in a variety of samples including flat test plaques, extruded tape, and tubing. Moreover, samples prepared using this new formulation had good dimensional stability; the percentage change in weight and dimensions remained low when measured at 37°C over 24 hours. While other technologies for imparting lubricity to low-durometer materials exist, they have a narrow process window when they are being tailored for a given application. You are limited to adding no more than 10% of an additive, because exceeding that percentage would result in screw slippage. These techniques-compounding low-durometer materials onto base polymers and applying coatings-have other drawbacks that may include base polymer swelling, coating migration, and possible cross contamination.