Friction Testing Methods for PTFE Catheter Liners

Catheter friction is the resistance that develops when two surfaces in contact move against each other during an interventional procedure.

A liner lines the internal lumen of a catheter. The two most desired features of these liners are ultra-thin walls and an extremely low coefficient of friction that helps devices glide smoothly through the catheter. Manufacturers use different friction testing methods to quantify the lubricity of catheter liners. For example, a PTFE liner is placed inside the catheter lumen, and the counterface, such as the guidewire, dilator, or instrument being pushed through it, is tested.¹ Apart from this simple test, manufacturers like Hydromer® use vertical and desktop friction testers for advanced measurements and enhanced reliability during operational procedures.

This article covers the main PTFE liner friction testing methods, what each one measures, and where each one falls short. We have also included the standards that apply, the variables that break repeatability, and guidance on matching a test to actual device use. Biomedical engineers, medical device manufacturers, and quality professionals should find it useful when setting up or defending a liner friction specification.

Key Takeaways

• Catheter friction is the resistance that develops when two surfaces in contact move against each other during an interventional procedure.
• A PTFE liner is an ultra-thin tube of polytetrafluoroethylene placed along the inner wall of the catheter lumen.
• As such, the type of PTFE liner friction testing heavily depends upon the counterface.
• The right test method mostly depends on the problems we are facing.

What is Catheter Friction?

Catheter friction is the resistance that develops when two surfaces in contact move against each other during an interventional procedure. Every catheter has two separate friction interfaces.

The outer wall meets the introducer sheath, the guide catheter, and the vessel wall as the device is advanced.

The inner lumen wall meets the guidewire, dilator, or secondary device being pushed through it.

We are focusing on the second one in this article. In general, friction is measured in two ways. The first is friction force, measured directly in grams or newtons as the device is moved through the lumen. The second is the coefficient of friction, which is the ratio of that friction force to the load pressing the two surfaces together.

Static vs. Dynamic Friction

Engineers also separate friction into static and dynamic.

Static friction is the force needed to start movement from rest.

Dynamic friction, also called kinetic friction, is the force needed to keep that movement going. Static is almost always the higher of the two.

The gap between these two values creates a behavior called stick-slip. The wire holds, the operator increases push force, and then the wire releases suddenly and jumps forward. In general, the goal is to keep static and dynamic friction close together, so the device travels smoothly instead of in steps.

Adverse Effects of High Catheter Friction

• Higher push force needed to advance the device
• Poor transmission of push and torque to the distal tip
• Loss of tactile feedback for the operator
• Jerky movement instead of smooth, continuous travel
• Surface wear and particulate generation
• Longer procedure times

The Role of PTFE Liners in Reducing Catheter Friction

A PTFE liner is an ultra-thin tube of polytetrafluoroethylene placed along the inner wall of the catheter lumen. It becomes the innermost layer of the device. Every wire, dilator, or instrument that travels through the catheter glides against the liner.

PTFE is chosen for this job because of its carbon backbone fully surrounded by fluorine atoms. That structure gives a chemically stable, non-polar surface with very little tendency to interact with the materials sliding across it. Additionally, PTFE is commonly known to be among the lowest-friction solids available for medical use.²

A guidewire advanced through a PTFE-lined lumen meets less resistance than the same wire in an unlined polymer lumen.³ As a result, the operator feels more of what is happening at the tip because less of the applied force is being consumed by friction along the shaft.

A few more properties of PTFE that reduce friction are as follows:

• Consistent Surface Finish: The liner is manufactured as a continuous tube through film casting, OTW extrusion, or free extrusion. This gives a uniform inner surface right from the proximal end to the distal tip.⁴
• Inherent Lubricity: PTFE is lubricious in its solid state. It does not need to be hydrated, wetted, or activated before use, and its surface does not depend on a fluid film staying in place during the procedure.⁵
• Mechanical Stability: Many procedures involve exchanging devices through the same catheter several times. The liner is a solid layer of material rather than a thin surface treatment, so it holds up through repeated insertion and withdrawal cycles under normal operating conditions.⁶

Note that a liner works on the inside only. It does nothing for the friction between the catheter’s outer wall and the vessel or the sheath. That interface is handled separately, usually through an outer hydrophilic coating. Both approaches are often used on the same device because they solve two different problems.⁴

Most Common Things that Pass Through a PTFE-Lined Catheter

The lumen of a catheter is a working channel. Different devices and materials travel through it during a procedure, and each one contacts the liner differently. You must plan what actually would move through the lumen before designing or finalizing the PTFE liner friction testing setup.

• Guidewires: The guidewire is the most frequent traveler through the lumen. It is usually stainless steel or nitinol, often with a polymer jacket or, in some cases, a coil-wound distal section. It moves back and forth repeatedly.
• Dilators: A dilator is a tapered polymer shaft advanced through the catheter to widen the access path. It fills much more of the lumen than a wire does.
• Secondary Catheters and Microcatheters: In many interventions, a smaller catheter is tracked through a larger one. The inner device presents a smooth polymer or coated outer surface to the liner.
• Stent and Implant Delivery Systems: Delivery systems carry a crimped stent, a coil, or an occluder to the treatment site. These have irregular outer profiles rather than a smooth cylinder.
• Balloon Catheters: A folded or rewrapped balloon travels through the lumen on its way to the lesion. The folded balloon has ridges and creases along its surface.
• Biopsy and Retrieval Instruments: Forceps, baskets, snares, and graspers pass through lumens in endoscopic and interventional devices. These are metal instruments with articulating joints and exposed edges.
• Fluids: Contrast media, saline, drugs, and embolic agents are injected through the lumen. Fluids do not create sliding friction in the same sense, but they change the interface.
• Aspirated Material: In thrombectomy and aspiration procedures, clot and debris are drawn back through the lumen under vacuum. Here the material moves in the reverse direction. The challenge here is to ensure they pass through without adhering to the wall.

Note that each of these presents a different material, a different contact geometry, and a different load to the same liner. A single friction number cannot describe all of them. As such, the type of friction test heavily depends upon the counterface.

Friction Testing Methods for Catheter PTFE Liners

Below are the most commonly used PTFE liner friction testing methods.

1. Sled and Plane Testing 

ASTM D1894 measures static and kinetic coefficients of friction for plastic film and sheeting. A weighted sled faced with the counterface material is drawn across a flat specimen while the pulling force is recorded.

It is simple, well documented, and useful for comparing PTFE grades or surface treatments. That said, it needs a flat specimen, so it cannot represent a wire moving through a curved lumen.

2. Pin-on-Disc and Reciprocating Sliding Tests

A tribometer presses a pin or ball of the counterface material against the specimen and slides it, either in rotation or back and forth. Force is recorded continuously over hundreds or thousands of cycles.

This shows how friction changes with distance and where wear begins, which a single-pass test cannot. The geometry is still simplified, so the output is best treated as material screening data rather than device performance.

3. Mandrel Pull-Through Testing

A wire or mandrel of known diameter is passed through the liner and drawn at a constant speed while force is measured. This is the most direct measurement of the surface that actually matters, because the test happens in the real lumen geometry.

The result depends heavily on the clearance between the mandrel and the inner diameter. Note that a liner with a slightly tighter ID will read higher force even if its surface is identical, so dimensional data has to be recorded alongside every result.

4. Pinch Grip Cycle Testing

Two pads grip the device at a set normal force while it is cycled through them, and the force is logged on every pass. Hydromer’s vertical and desktop friction testers work this way and are compliant with YY/T 1898-2024, the industry standard for hydrophilic coating fastness on intravascular catheters and guidewires.

Note that this is an outer surface method by design. Its value for liner work is the cycling protocol, which shows whether friction climbs across repeated passes rather than reporting one number from a single stroke.

5. Tortuous Path Simulated Use Testing

The catheter is routed through a curved anatomical track fixture and the inner device is advanced while force is recorded. ASTM F2394 describes a fixture of this type for stent delivery system work, and similar tracks are widely built in-house for other devices.

This is the closest a bench test comes to procedural conditions. That said, the measured force combines liner friction with bending stiffness, braid behavior, and outer surface drag, so it does not isolate the liner.

6. Insertion and Withdrawal Force Testing on the Finished Device

The finished catheter is tested with the actual device it will carry, and force is recorded in both directions. Withdrawal is often the harder pass, particularly with folded balloons and expanded implants.

This sits at the design verification level and answers the question a reviewer will ask. It cannot tell you whether a problem came from the liner, the bond, or the geometry, so it works best alongside one of the isolating methods above.

Note that no published standard covers friction measurement inside a PTFE-lined lumen specifically. ASTM D1894 was written for film, YY/T 1898-2024 was written for hydrophilic coatings, and ASTM F2394 was written for stent securement.

Each one gets adapted, and the adaptations vary across different suppliers.^{7 8}

Key Variables That Change Your Friction Test Results

Test-side variables:

• Counterface Material and Geometry: The material and shape sliding against the liner drive the result more than any other factor.
• Test Medium and Lubrication State: Dry, saline-filled, and contrast-filled lumens each produce different readings.
• Sliding Speed: PTFE friction is speed-dependent, and slow advancement often reads higher than fast advancement.
• Normal Load and Contact Force: Set directly by the fixture in grip tests, and by lumen clearance in pull-through tests.
• Temperature and Conditioning: Room temperature and body temperature give different results, and polymer counterfaces soften as they warm.
• Cycle Count and Break-In: The first pass reads highest, then friction settles before wear pushes it back up.

Liner-side variables:

• Manufacturing Process: Film casting, OTW extrusion, and free extrusion produce different molecular arrangements and surface characteristics.
• Inner Surface Finish: Die lines, mandrel marks, and sintering variation raise real contact area without showing up in dimensional inspection.
• Inner Diameter and Clearance: A tighter inner diameter raises contact force and therefore raises measured friction.
• Concentricity and Wall Uniformity: An off-center lumen loads one side of the wall more, causing uneven wear and inconsistent repeat readings.
• Surface Treatment Placement: Etching belongs on the outer surface only, since any etchant reaching the lumen raises friction.
• Downstream Processing: Reflow, lamination, and tipping expose the liner to heat and pressure after extrusion.
• Sample Handling and Contamination: Mold release, skin oils, packaging residue, and cleaning solvents all sit on the surface being measured.

How to Select the Right Friction Test Method for Your Device

The right test method mostly depends on the problems we are facing. Material selection, process control, and design verification each need something different, and using one method for all three leads to data that does not support any of them well.

• Material and Supplier Screening: Use sled and plane or reciprocating tribometer testing to rank options under controlled conditions.
• Incoming Inspection and Lot Release: Use mandrel pull-through testing and record inner diameter with every result.
• Process Development: Use pull-through testing with a fixed mandrel diameter, adding cycling to check durability.
• Design Verification: Use insertion and withdrawal force testing on the assembled device with its actual companion device.
• Failure Investigation: Work backwards from the finished device, to the bare liner, to a retained sample from the same lot.
• Counterface: Use the device that will actually pass through the lumen, or the closest practical substitute.

Hydromer®: Advanced PTFE Liner Manufacturer and Friction Testing Equipment Supplier

Hydromer®, Inc. has spent more than 40 years working on the surfaces of medical devices. That work now covers PTFE liners for catheter lumens, hydrophilic coatings, automated coating systems, friction testing equipment, and contract services.

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 PTFE liners through three processes: Free Extrusion, Over-The-Wire (OTW) Mandrel Extrusion, and Film Casting. Each route gives a different balance of rigidity and flexibility, which lets the liner be matched to the device rather than the other way around.

Below are the top five benefits of selecting Hydromer® PTFE liners:

• Tight Dimensional Control: Inner diameter tolerance as low as ±0.0003 inches (7.6 μm) and wall thickness tolerance as low as ±0.00025 inches (6.35 μm).^{9 10} Since lumen clearance directly changes measured friction, holding dimensions this tightly keeps your test data pointing at the surface rather than at dimensional drift.
• Lot-to-Lot Repeatability: Scalable extrusion lines with inspection built into every stage. A friction specification only holds if the liner behind it stays the same from batch to batch.
• Fast Prototype and Sample Supply: Rapid prototyping and dedicated production capacity, so you can get material in hand early and develop your test method against real samples instead of assumptions.
• Support Across Development and Measurement: Engineering support, design for manufacturability, material formulation, regulatory services, prototyping, validation, and full-scale manufacturing. We also supply complementary products such as hydrophilic medical device coatings and vertical and desktop friction testers compliant with YY/T 1898-2024.
• Premium Fluoropolymer Grades: High-grade fluoropolymers selected for lubricity, biocompatibility, and consistent surface behavior under normal operating conditions.

Please feel free to contact our Hydromer® team to learn more about PTFE liners or to request samples.

Contact Hydromer®

FAQ About PTFE Liner Friction Testing

References:

View all references (10 peer-reviewed & industry sources)

1. Marmieri, G., Pettenati, M., Cassinelli, C., & Morra, M. (1996). Evaluation of slipperiness of catheter surfaces. Wiley Online Library. https://onlinelibrary.wiley.com/doi/abs/10.1002/(SICI)1097-4636(199621)33:1%3C29::AID-JBM5%3E3.0.CO;2-O
2. Ullah, S., Haque, F. M., & Sidebottom, M. A. (2022). Maintaining low friction coefficient and ultralow wear in metal-filled PTFE composites. Wear, 498–499, 204338. https://doi.org/10.1016/j.wear.2022.204338
3. jMedtech Coating Technologies Pte Ltd. (n.d.). PTFE liner selection guide: How to choose the right liner tubing for interventional devices. https://jmedtech.com/news/PTFE-Liner-Selection-Guide-How-to-Choose-the-Right-Liner-Tubing-for-Interventional-Devices.html
4. Hydromer, Inc. (2026, July 13). PTFE liners & PTFE tubing for medical devices | Hydromer. Hydromer. https://hydromer.com/ptfe-liners-and-tubing/
5. INVAMED Medical Affairs (2026). PTFE liners: The slippery secret inside catheters. INVAMED. https://invamed.com/news/ptfe-liners-lubricity
6. Rucker, D. G., Lee, S., Qiu, M. Y., Huang, Y., Becerra-García, J., Jin, H., Suskin, C. B., Connor, M., Pyeatte, S., Osbun, J. W., Zayed, M. A., & Genin, G. M. (2026). Multiscale architecture governs stability in Suction-Actuated variable stiffness catheters. Journal of Biomechanical Engineering, 148(7). https://doi.org/10.1115/1.4071866
7. Standard test method for static and kinetic coefficients of friction of plastic film and sheeting. (n.d.). https://store.astm.org/d1894-24.html
8. Zheng, W. (2026, July 3). YY/T 1898-2024 English PDF Translation. Chinesestandard.net. https://www.chinesestandard.net/PDF.aspx/YYT1898-2024
9. Hydromer, Inc. (2026, July 29). Precision PTFE Extrusion for Medical Tubing & Devices. Hydromer. https://hydromer.com/precision-ptfe-extrusion/
10. 10.Standard Guide for Measuring Securement of Balloon-Expandable Vascular Stent Mounted on Delivery System. (n.d.). https://store.astm.org/f2394-07r22.html