Liner material selection directly impacts how a device performs inside the body. In this article we explore the most common types of medical device liner materials, including PTFE, HDPE, and polyimide liners. We will explore the properties of each material, their benefits, and where they are best suited in medical device applications. This article is intended to help biomedical engineers and medical device manufacturers make informed material and product design decisions.
What are Medical Device Liners?
Medical liners are simple yet incredibly vital components of many catheters and minimally invasive devices. Unlike standalone tubing, liners are thin tubes placed along the inner wall of the lumen. They create a smooth, low-friction surface for guidewires, fluids, and other instruments to travel through. Without liners, the inner surface of these devices would generate too much friction, which hampers navigation of other devices or delivery of fluids and medications.
Liners are used in various devices. These include catheters, endoscopes, biopsy tools, guidewire delivery systems, and surgical instruments. They form ultra-thin layers within the inner lumen of these minimally invasive devices.
Their primary function is to enable a safe passage for devices, medications, and biological fluids. Liners are not standalone devices. Instead, they are critical sub-components that directly influence overall device performance.
The functionalities of a liner vary by the type of material used. For example,
- PTFE offers the lowest coefficient of friction
- HDPE provides a cost-effective balance of strength and lubricity
- Polyimides deliver high tensile strength with ultra-thin walls
At Hydromer®, we offer PTFE liners and tubings produced through the Free Extrusion, Over-The-Wire (OTW) Extrusion, and Film Casting methods. Our goal is to ensure a perfect balance of lubricity, strength, flexibility, and wall thickness.
The Importance of Liners in Catheters and Minimally Invasive Medical Device Performance
All minimally invasive procedures rely heavily on small, flexible devices for their success. They need to travel through highly torturous anatomical pathways and, at the same time, carry other devices or deliver critical fluids to the target site. Any unnecessary friction inside the lumen of these devices can cause issues. These include compomised physician control, extended procedure time, and increased patient risk.
Liners address these challenges by reducing friction between the device wall and passing instruments or fluids. This directly enhances trackability, pushability, and overall performance.
Liners also protect the device’s inner wall from chemical interactions with drugs, contrast agents, and/or biological fluids. In applications such as electrophysiology catheters and neurovascular systems, liners also help maintain dimensional stability under repeated mechanical stress.
The choice of liner material directly impacts how a device performs inside the body. In turn, we discuss the types of liner materials below in more detail.
Types of Liner Materials Used in Medical Devices
Liners are manufactured from various materials, each offering distinct chemical, mechanical, and biological properties. Careful material selection is essential to meet specific application requirements.
Below are the three most common materials used in medical device liners today:
1. PTFE (Polytetrafluoroethylene)
The PTFE is undoubtedly the most preferred material for medical device liners used in high-performance minimally invasive applications. It has one of the lowest COF (coefficients of friction) of any solid material, approximately 0.04. This means no additional inner coating is needed.
PTFE is chemically inert to acids, bases, solvents, and biological fluids, making it a safe choice for fluid-contact applications. It is ideal for devices requiring minimal resistance and low contamination risk during guidewire, instrument, or fluid passage.
2. HDPE (High-Density Polyethylene)
HDPE is a cost-effective alternative to PTFE, offering a balance of lubricity, strength, and flexibility. However, it provides lower friction performance and thermal stability, limiting its use in high-performance or high-temperature applications.
HDPE is easier to process using standard extrusion methods than PTFE, making it practical for high-volume manufacturing. It is commonly used in diagnostic catheters, drainage systems, peripheral vascular catheters, and other devices requiring moderate lubricity and chemical resistance.
3. Polyimide (PI)
PI or Polyimide is used in applications that require very high tensile strength, dimensional precision, and ultra-thin wall construction. It has excellent mechanical properties and offers exceptional performance under high-temperature and high-pressure conditions.
One thing to note here is that the polyimide has a higher coefficient of friction compared to PTFE. This means instruments and guidewires passing through a PI liner experience more resistance. As a result, polyimide is sometimes combined with a PTFE inner layer in hybrid or multi-layer liner constructions.
Polyimide liners are particularly suited where a thin but strong inner layer is critical. Examples include microcatheters, coil delivery systems, neurovascular tools, electrophysiology catheters, and high-pressure balloon catheters.
Liner Material Selection For Common Applications of Medical Device Liners
Medical device liners play a silent but critical role across a wide range of minimally invasive procedures, from cardiovascular intervention to neurovascular surgery. Liners are the inner layer that makes it possible for instruments, fluids, and guidewires to move through devices safely and reliably. And liner material selection plays a critical role in the performance of devices and the success of the procedure.
Below are common devices that use liners to ensure smooth and safe operation. We give an overview of the applications as well as guidance on liner material selection.
1. Catheters
Many types of catheters rely on liners to reduce friction and maintain reliable performance as guidewires, instruments, and fluids pass through the inner lumen.
a. Guiding Catheters
Guiding catheters are used to provide a safe pathway for the delivery of interventional devices to a target site.
Material Selection:
PTFE liners inside the guiding catheter creates a smooth, stable inner lumen. This allows guidewires, balloon catheters, and stent delivery systems to pass through with minimal friction.
b. Diagnostic Catheters
Diagnostic catheters are used to deliver contrast agents and monitor pressure inside the cardiovascular system. The liner inside a diagnostic catheter ensures smooth fluid flow and prevents any chemical interaction between the contrast agent and the catheter wall.
Material Selection:
Based on the performance requirements, manufacturers can choose between PTFE or HDPE liners for diagnostic catheters.
c. Neurovascular Microcatheters
These very small catheters require liners that minimize friction. Even slight resistance can cause microwires to buckle or coils to jam.
Material Selection:
PTFE liners are preferred for their low friction, enabling precise advancement, positioning, and retraction of devices without sticking.
d. Electrophysiology Catheters
Electrophysiology catheters are used in cardiac mapping and ablation procedures. These devices carry electrical leads, irrigation fluids, and pressure monitoring simultaneously through separate lumens.
Material Selection:
PTFE liners ensure that fluids and instruments pass through each lumen without friction or chemical interaction, helping ensure accurate signal delivery and reliable device performance throughout the procedure.
e. Balloon Catheters
Balloon catheters are used in angioplasty, valvuloplasty, and other procedures where a balloon is inflated at a target site to open a blockage or support a structure. The liner inside the shaft of a balloon catheter allows the guidewire to pass through smoothly during advancement and withdrawal.
Material Selection:
PTFE is commonly used for this due to its chemical inertness and low friction properties.
f. Urological Catheters and Drainage Systems
Urological devices require liners that can withstand prolonged exposure to biological fluids while maintaining smooth fluid flow and dimensional stability.
Material Selection:
PTFE and HDPE liners are both used in urological applications, depending on the required flexibility and performance level.
2. Endoscopes and Endoscopic Tools
Nearly all endoscopes have multiple working channels through which biopsy forceps, snares, and other instruments are passed.
Material Selection: PTFE liners inside these working channels ensure smooth passage for instruments without wear or contamination. The chemical inertness of PTFE also helps ensure the liner does not interact with irrigation fluids or tissue samples passing through the channel.
3. Biopsy Devices and Needle Guides
Biopsy needles and needle guide systems use liners to ensure smooth passage for the needle through the guide shaft.
Material Selection: A low-friction liner, such as PTFE reduces the force required to advance the needle. This improves physician control and reduces the risk of tissue trauma during the biopsy procedure.
4. Drug Delivery and Infusion Systems
Drug delivery systems use liners as the primary fluid pathway.
Material Selection: PTFE liners are the best choice here because of their properties. They are generally considered not to react with sensitive medications, contrast agents, or biological fluids, helping ensure drug integrity and accurate delivery to the target site.
Considerations When Choosing a Liner Material for Your Minimally Invasive Medical Devices
Each medical device has specific design, clinical, and regulatory requirements, which will influence material choice. Liner material selection also heavily depends upon them. Below we discuss some important factors to consider when selecting liner material and construction.
Lubricity
Devices requiring frequent advancement and retraction of guidewires or fluids need liners with the lowest possible coefficient of friction. PTFE is preferred for high lubricity needs, while HDPE is suitable for moderate requirements. PI has the highest CoF of the three.
Wall Thickness
In minimally invasive devices, minimizing wall thickness maximizes usable inner diameter and instrument compatibility. Manufacturers should select liner materials and processes that achieve the required thickness without compromising strength or consistency (or lubricity). Hydromer® produces PTFE liners with wall thickness as low as 0.00635 mm and inner diameter tolerances of ±0.0051 mm, maximizing lumen space and performance.
Chemical Inertness
The liner material must be compatible with all fluids, drugs, and agents that will pass through. Any chemical interaction between the liner and the substance passing through it can contaminate the fluid, degrade the liner, or compromise patient safety.
Mechanical Stability
Liners must maintain structural integrity under normal operating conditions, kink-resistance, deformation, and collapse during flexing. High tensile strength is essential for devices subjected to pull forces. Polyimide liners offer the highest tensile strength, along with flexibility and kink-resistance, making them ideal for high-pressure or demanding applications.
Sterilization Compatibility
The liner material must be compatible with the sterilization method used for the parent device. PTFE is compatible with both autoclave and ethylene oxide sterilization. HDPE is generally compatible with ethylene oxide but has limited compatibility with high-temperature sterilization methods.
Biocompatibility
Liners that come in contact with human tissue or body fluids must meet strict biocompatibility standards. Both the liner material and the manufacturing process need to be validated against relevant standards such as ISO 10993. In the case of materials like PTFE, which are non-toxic and non-carcinogenic, manufacturers can easily comply with the regulatory requirements.
Liner Material Alternatives: Hybrid or Multi-layer Liners for Advanced Applications
Hybrid or multi-layer liners combine the strengths of multiple materials in a single construction. This is done to maximize device performance for advanced minimally invasive procedures.
For example, most manufacturers combine a PTFE inner layer with a polyimide or other high-strength outer layer. The PTFE inner layer provides the inherently low-friction surface needed for the smooth passage of guidewires and instruments through the lumen. The outer layer adds the mechanical strength, dimensional stability, and kink resistance that PTFE alone cannot always deliver in very thin-wall constructions.
Manufacturing hybrid liners requires advanced process expertise and stringent quality control. Consistent and reliable bonding between layers is essential, making it important to partner with an experienced manufacturer.
Hydromer®: Advanced PTFE Liner and Hydrophilic Coating Manufacturer
Hydromer®, Inc. is a leading hydrophilic coatings manufacturer and supplier with over 40 years of experience. Recently, Hydromer® has expanded into PTFE liner manufacturing through a strategic partnership with jMedtech, combining decades of coating expertise with precision extrusion capabilities to offer device manufacturers a more complete material solution.
Our comprehensive product portfolio includes advanced PTFE liners and tubing, along with custom hydrophilic coatings, automated coating equipment, and comprehensive contract coating services.
We are able to support device manufacturers, regardless of what stage of the product development lifecycle they are in.
Our PTFE Liner Products include:
- MatrixLiner® Free Extruded Liner
- MatrixLiner® Extruded OTW Liner
- MorphoLiner® Casted OTW Liner
5 Top Advantages of Choosing Hydromer®, Inc. PTFE Liners
Hydromer® manufactures ultra-thin-wall PTFE liners using Free Extrusion, Over-The-Wire (OTW) Mandrel Extrusion, and Film Casting. The process is chosen based on your device’s mechanical and dimensional requirements. Our engineers will select the appropriate process based on different application scenarios and catheter designs. This process is done to better match the combination of size, strength and flexibility to meet your specific application needs, providing medical device manufacturers with more options for designing medical devices of the next-generation.
Below are the top five benefits of selecting Hydromer® PTFE Liners:
- Reliable Extrusion Lines: Our production lines are built for precise micro-dimensional extrusion, with wall thickness as low as 0.00635 mm and inner diameter tolerances as tight as ±0.0051 mm, supported by advanced quality inspection at every stage of production.
- Scalable Output: From prototype to high-volume production, our extrusion lines maintain reliable dimensional accuracy and consistent performance across every batch.
- Accelerated Timelines: Rapid prototyping capabilities and dedicated production lines allow us to support faster development cycles without compromising on quality or precision.
- End-to-End Support: Our capabilities go beyond extrusion. We offer engineering support, design for manufacturability, regulatory services, material formulation, prototyping, testing, validation, and full-scale manufacturing, all under one partnership.
- Premium Fluoropolymers: We use only high-grade fluoropolymers that meet the biocompatibility, lubricity, and long-term reliability requirements of medical device applications.
Get In Touch
Hydromer’s PTFE liners, hydrophilic coatings, coating equipment, and contract services are designed to support your device from early development through to full-scale production.
Please feel free to contact Hydromer® to learn more about our PTFE liner products or to request samples.
