A catheter is a slender, flexible tube intended for insertion into a body cavity, duct, or vessel. The primary purpose of these devices is to manage fluids, including draining fluids, delivering medications or other substances, or providing access for surgical instruments and procedures. Because catheters interact directly with delicate biological systems, the materials used are paramount for patient safety, flexibility, and the required duration of use. Modern material science provides a diverse range of polymers and specialized components, each selected to optimize the device for its specific medical application.
Primary Materials: Synthetic Polymers
A wide variety of synthetic plastics forms the foundational structure for most catheters, chosen for their specific blend of rigidity, flexibility, and cost. Polyvinyl Chloride (PVC) is frequently used for short-term catheterization and disposable devices due to its cost-effectiveness and ease of manufacturing. While rigid in its raw form, the addition of plasticizers allows PVC to be manufactured into flexible, resilient tubing that is chemically stable. This material is commonly seen in uncoated intermittent catheters, where its affordability makes it a practical choice for single-use applications.
Polyurethane (PU) represents a versatile class of polymers valued for their strength and flexibility, often used for catheter shafts and balloons. PU polymers boast a broad hardness range, making them suitable for devices that require both a firm structure for insertion and a softer component for patient comfort. These materials are known for their excellent biocompatibility. PU is frequently utilized in central venous and arterial catheters that require a balance of pushability and pliability.
Polytetrafluoroethylene (PTFE), known as Teflon, is a fluoropolymer with an exceptionally low coefficient of friction. This “non-stick” quality makes it invaluable for creating smooth inner liners, particularly in vascular and guiding catheters. By lining the interior of a catheter with PTFE, manufacturers ensure that guidewires, balloons, or stents glide through the tube with minimal resistance. This reduces the risk of tissue damage during complex procedures.
Silicone and Natural Rubber Latex
Materials for long-term implantation prioritize biocompatibility and inertness to minimize the body’s reaction over extended periods. Silicone is a synthetic polymer characterized by its smooth surface, high resistance to chemical degradation, and superior biocompatibility. This makes it a preferred choice for devices intended to remain in the body for weeks or months. Its non-porous surface naturally resists the formation of biofilms and encrustation, which are common complications in long-term indwelling devices like Foley catheters.
Natural rubber latex, while historically a common material for catheters, is now used less frequently due to safety concerns. Latex offers high elasticity and a soft texture, which can provide a comfortable fit and flexibility for certain short-term applications. However, the proteins present in natural rubber can trigger Type I hypersensitivity reactions in sensitized individuals. The risk of these allergic reactions has driven the medical field toward safer synthetic alternatives, particularly silicone, for most patient populations.
Enhancements and Specialized Components
Specialized components and surface modifications are applied to enhance catheter performance and safety. Surface coatings are commonly applied to bulk materials to improve the catheter’s interaction with the body’s tissues and fluids. Hydrophilic coatings, for instance, become exceptionally lubricious when exposed to water. This significantly reduces friction during insertion, minimizing urethral trauma and patient discomfort.
Antimicrobial coatings are used to combat the high risk of infection associated with indwelling devices, such as catheter-associated urinary tract infections. These coatings may incorporate silver or silver-releasing compounds, which possess broad-spectrum antimicrobial properties to inhibit bacterial colonization. Other approaches involve embedding contact-killing agents or developing non-leaching cationic polymer surfaces that disrupt bacterial cell membranes upon contact.
Metals are utilized as internal structural elements or accessories, not typically for the main tubing. Specialized catheters, such as those used in cardiology, often incorporate braided or coiled wires made from stainless steel or nickel-titanium alloy (Nitinol). These metal reinforcements provide torque control and increased pushability, allowing the clinician to navigate complex vascular structures. Radiopaque materials like platinum or tungsten are integrated into catheter tips or marker bands for clear visibility under fluoroscopy during precise placement procedures.