Reinforced catheter design combines a PTFE liner with metallic or polymeric braid or coil reinforcements to create a shaft that meets tough clinical and manufacturing standards. Modern catheters deploy this reinforced shaft design to balance flexibility, pushability, torque response, and kink resistance.
Key Takeaways
- If a catheter is not reinforced, “it runs the risk of buckling or collapsing in clinical procedures.”
- Braided reinforcement “has outstanding flexibility and torque capabilities,” while coil reinforcement “offers extreme levels of flexibility, providing lumen integrity while bending.”
- PTFE liner thickness is “one of the most important design decisions” — thinner liners “maximize lumen diameter” and improve flexibility, while thicker liners “provide improved dimensional stability.”
- Because PTFE “cannot be bonded with adhesives in a reliable manner” in its natural state, etching is “a critical post-extrusion surface treatment that prepares PTFE for bonding during catheter assembly.”
Modern medical procedures are increasingly becoming minimally invasive. These procedures require catheters that can maneuver safely through complex anatomy. At the same time they must provide an optimum combination of flexibility, pushability, torque response, kink resistance, dimensional stability, and lifespan. This is a formidable engineering challenge because the improvement of one property usually comes at the expense of the others.
In the article, we use Hydromer®, Inc.’s 40+ years of materials expertise to explore the design challenges of reinforced catheters. We will explore the interaction between PTFE liners and reinforcement layers, and how these components influence the quality of the devices. If you are a medical device engineer you will definitely want to read to the end of this article.
The Role of PTFE Liners in Reinforced Catheter Construction
PTFE liners are the preferred liner for various interventional catheters. This is due to the liners’:
- Low coefficient of friction and lubricity
- Remarkable chemical resistance
- Impressive thermal stability
- Remarkable biocompatibility
It is important to note that in a catheter shaft, PTFE is the innermost layer. It provides a smooth pathway for guidewires, balloons, stents, microcatheters, and other therapeutic devices to pass through.
The most important function the PTFE liner provides is to reduce friction when the device is being advanced or pulled back. Less friction means:
- better delivery of the device
- lower forces during insertion
- better control by the surgeon
- less wear of the catheter and the device as it passes through.
PTFE liners have minimal contribution to catheter rigidity due to its low modulus of elasticity. Instead they are a tribological component whose performance greatly depends on the effectiveness of its interaction with the absorbing coverings. Today, modern PTFE liners are made using precision extrusion methods. These allow for very strict tolerances in terms of wall thickness, concentricity, and internal diameter.1,3
How the different components of reinforced catheter work together
Within a catheter the PTFE liner, reinforcement layer, adhesive tie layers, and outer polymer jacket do not act as separate elements. Instead, they work together as an integrated composite structure. The joint characteristics of all the components define the mechanical performance, lubricity, bond strength, and reliability of the catheter.2 This means that proper optimization of parameters like the liner thickness, the geometry of reinforcements, compatibility of the polymers used, and gluing technologies is essential for effective catheter development.
Why is Catheter Reinforcement Necessary?
If the catheter is not reinforced, it runs the risk of buckling or collapsing in clinical procedures. 4,5
Why?
PTFE liners have excellent properties regarding lubricity. However, they lack the necessary mechanical strength to perform well in difficult interventional applications. PTFE is quite soft and does not have high tensile, compression, and twisting resistance.
In order to solve these shortcomings, the manufacturers use reinforcement layers between the PTFE liner and polymer outer jacket. Reinforcement layers provide the following significant improvements to the catheter:
- Torque transmission
- Pushability
- Kink resistance
- Radial strength
- Burst pressure
- Tensile strength
- Dimensional stability
The most appropriate type of reinforcement architecture greatly depends on the specific medical problem, the diameter of the catheter, the required flexibility, and the complexity of navigation. Below we will look at the details of constructing reinforced catheters and how the different components interact.
Composite Catheter Construction
Reinforced catheters can be regarded as a composite structure. They are constructed of different layers of specialized materials. Each one is used to serve a specific purpose.
The PTFE liner provides lubrication and chemical protection. The liner is reinforced with either a metal or polymer reinforcement layer that is usually either woven (braided) or wire-like in shape. Then the whole construction is then finally covered in a polymer jacket, usually made of Pebax®, polyurethane, nylon, or other thermoplastic elastomers.6-8
Options for Reinforcing the PTFE Liner
As mentioned earlier, the catheter’s PTFE liner is treated and a reinforcement layer is added over it. This consists of either a metal or polymer reinforcement layer, which is usually either woven (braided) or wire-like in shape. We discuss the different catheter reinforcement layer options below in more detail.
1. Braided Catheter Reinforcement
Braided reinforcement has outstanding flexibility and torque capabilities. As a result, it is indispensable in the construction of guide, delivery, aspiration, and support catheters.
Braided reinforcement is woven at particular braid angles and placed over the treated PTFE Liner. The braid is made of stainless steel, nitinol, or newer materials, such as aramid or liquid crystal polymers.
The braid angle determines how the catheter will behave.
- Smaller braid angle causes longitudinal rigidity and pushability to increase
- Higher braid angle will increase flexibility, but it decreases the efficiency of torque transfer
The braid is placed on the PTFE liner in a process that consists of placing a core mandrel, treating the liner, braiding the reinforcement layer, and then securing the composite with an outer jacket.
It should be noted that thin liner walls may cause some wires to penetrate the liner, which can create local stress areas. However, thin liners are critical to minimally invasive catheters. Increasing the thickness of the PTFE liner will increase the profile of the catheter and reduce the flexibility of the shaft.5,9
2. Coil Catheter Reinforcement
Coil reinforcement presents a fundamentally different mechanical profile than braided reinforcement techniques. Coil-reinforced catheters use helical wires instead of woven wires. They are built using a helical wire wrapped around the PTFE liner.10,11
Coils offer extreme levels of flexibility, providing lumen integrity while bending. The coil can contract and elongate during movement. In turn, coil-reinforced shafts tend to achieve more compliant bending properties over braided alternatives.11,12
One of the main merits of using coil reinforcement is that it improves the lumen resilience without increasing the shaft rigidity too much.
The PTFE liner in the tube of the coil ensures low friction. The coil keeps the lumen in a round shape while bending.11
Braided vs. Coil Comparison
| Reinforcement Type | Key Property | What the Article Says |
|---|---|---|
| Braided | Flexibility + Torque | “Braided reinforcement has outstanding flexibility and torque capabilities.” |
| Braided | Best Use Case | “It is indispensable in the construction of guide, delivery, aspiration, and support catheters.” |
| Coil | Flexibility Profile | “Coils offer extreme levels of flexibility, providing lumen integrity while bending.” |
| Coil | Bending Behavior | “Coil-reinforced shafts tend to achieve more compliant bending properties over braided alternatives.” |
Influence of PTFE Liner Thickness on Reinforcement Performance
Alongside liner material selection, PTFE liner thickness is one of the most important design decisions when it comes to reinforced catheter development.11,13 The decision has implications of the performance attributes of the catheter.
Engineers typically try to optimize liner thickness by balancing several competing requirements, including:
- Internal lubricity
- Catheter profile
- Mechanical durability
- Reinforcement support
- Manufacturing consistency
How PTFE Liner Thickness Effects Catheter Performance
Below are the main pros and cons of thin and thick PTFE catheter liners.
Pros of thin liners:
- maximize lumen diameter
- improve catheter flexibility
- minimize the overall catheter profile
Cons of excessively thin liners:
- may deform during braid application
- collapse under vacuum
- experience localized wear during repeated guidewire movement
Pros of thicker liners3,12,14:
- provide improved dimensional stability
- enhanced wear resistance
Cons of thicker liners:
- reduce internal lumen size
- increase shaft stiffness
Optimizing Reinforced Catheter Design Through Reinforcement Architecture.
The reinforced catheter’s performance is ultimately determined by the interaction of all its structural components rather than any single material. 1,13,15 In turn, the catheter’s mechanical properties can be fine-tuned through engineering design decisions. For instance:
- Pushability depends largely on reinforcement stiffness, outer jacket modulus, and the support provided by the PTFE liner
- Torque transmission is influenced by braid architecture, reinforcement material, and bond integrity between layers
- Kink resistance results from reinforcement geometry working together with polymer flexibility
- Burst pressure depends on how effectively reinforcement distributes internal stresses while preventing radial expansion of the PTFE liner
- Fatigue resistance is influenced by cyclic interactions between reinforcement wires, polymer jackets, and the liner during repeated bending.
Manufacturing Considerations For Reinforced Catheters
A high degree of precision is required in the production of reinforced PTFE-lined catheters. The ultimate performance of the catheter is affected by various process parameters. These include temperature, pressure, wire tension, reflow time, and cooling rate. 16
Below we look at the process of manufacturing these reinforced catheters as well as some of the challenges.
Manufacturing Process of PTFE-Lined Reinforced Catheters
- Material selection: High-quality PTFE is selected for its lubricity, chemical resistance, and durability.
- Extrusion: PTFE is heated and extruded through a die to produce thin-walled tubing that serves as the catheter liner.
- Assembly: The PTFE liner is integrated into catheter shafts made from materials such as PEBAX®, TPU, or nylon, often reinforced with metallic braids or coils. The process consists of:
- Placing a core mandrel inside the PTFE liner
- Adding a tie layer to the outer surface of the liner
- Reinforcement layers is added
- Outer polymer jacket is added as well as a heat-shrink layer, which holds the composite together
- Quality control: Finished catheters undergo rigorous inspection to verify liner integrity, dimensional accuracy, and compliance with medical standards.
Bonding Challenges Between PTFE and Reinforcement Layers
One of the biggest problems in the manufacture of PTFE catheters is the reliable adhesion of the inner PTFE liner to other materials. This is because PTFE has an extremely low surface energy compared with that of standard engineering polymers. Because of this, PTFE in its natural state cannot be bonded with adhesives in a reliable manner. This would result in a number of problems, such as the separation of the layers, delamination, liner migration, or loss of torque transfer.2
Today, manufacturers have created processes to successfully solve the above issues. They use activation techniques to increase the surface energy of PTFE. These include plasma discharge, sodium etching, and other special chemical treatments. Furthermore, the use of tie-layer adhesives and modified fluoropolymers allows for better adhesion properties.
PTFE etching is critical to solving these bonding issues. We discuss it in more detail below.
Importance of PTFE Etching
- PTFE etching is a critical post-extrusion surface treatment that prepares PTFE for bonding during catheter assembly
- Untreated PTFE has very low surface energy, making it difficult for adhesives to bond to it effectively
- Proper etching improves catheter reliability and helps prevent bond failure that could compromise device performance
Benefits of PTFE Etching
- Improves adhesion between the PTFE liner and the catheter shaft
- Activates the PTFE surface by increasing surface energy and introducing functional groups
- Enhances bonding with polymers, metals, elastomers, adhesives, and coatings
- Can improve lubricity through controlled surface modification
- Promotes wettability, allowing better interaction with liquids and coating materials
- May enhance biocompatibility by improving interactions with biological tissues and fluids
- Provides precise control of surface roughness to optimize performance for specific applications
Emerging Trends in Reinforced PTFE Catheter Design
The development of minimally invasive therapies has fostered innovation in catheter architecture. Device designers are using various density layers, braids, coils, and laser patterns to create catheter structures that are firmer at one end and softer on the other.
Material innovations also enhance the production capabilities of designs. Ultra-thin PTFE liners, strong nitinol micro-brass, plastic composite reinforcements, and various radiopaque elements enable engineers to reduce the size of the catheter. Also, manufacturing improvements in surface treatment and bonding technologies help increase the reliability of the connection of the walls and other components.17
Hydromer’s Advancements in Reinforced Catheter Technology
Hydromer Inc.’s innovations in catheter technology are helping to enhance reinforced PTFE-lined catheter design. Hydromer reliably manufactures high-performance, ultra-thin extruded PTFE liners (such as their ToughFlex® and ElastiFlex® series). When reinforced with braided or coiled reinforcement structures they optimize catheter shaft mechanics and performance attributes.
In addition to our portfolio of PTFE products, our custom hydrophilic medical coatings work well with standard parts of catheter jackets like Pebax®, polyurethane, and nylon..
As a result, Hydromer serves as a multi-solution OEM component supplier and coating specialist for medical device manufacturers.
Contact our PTFE experts with any questions or to request samples.
Conclusion
Reinforced catheter design requires complex materials engineering, mechanical design, and precision manufacturing. The PTFE liner, reinforcement layer, and outer polymer jacket function as a unified composite system, not individual pieces. The interaction between PTFE liners and braided or coiled reinforcement structures is fundamental to achieving the optimal balance of lubricity, flexibility, pushability, torque response, kink resistance, and structural integrity required for modern minimally invasive procedures.
Liner thickness, reinforcement geometry, bonding strategies, and material selection all require careful optimization. But they enable engineers to tailor catheter performance to specific clinical applications. Computational modeling, advanced manufacturing technologies, and novel reinforcement materials continue to advance. However, the synergy between PTFE liners and reinforcement architectures will remain central to the development of next-generation interventional catheters.
Editorial & Technical Review Board
To ensure the highest standards of engineering precision and scientific accuracy, this article was reviewed, validated, and approved by:
- Mike Torti, Chief Executive Officer
- Anthony Millan, Senior Technical Product Manager
- Paul McCue, Vice President – International Business Development
FAQ
If the catheter is not reinforced, it runs the risk of buckling or collapsing in clinical procedures… PTFE liners have excellent properties regarding lubricity. However, they lack the necessary mechanical strength to perform well in difficult interventional applications.
Braided reinforcement has outstanding flexibility and torque capabilities… Coil-reinforced catheters use helical wires instead of woven wires… Coils offer extreme levels of flexibility, providing lumen integrity while bending.
PTFE has an extremely low surface energy compared with that of standard engineering polymers. Because of this, PTFE in its natural state cannot be bonded with adhesives in a reliable manner… Etching is a critical post-extrusion surface treatment that prepares PTFE for bonding during catheter assembly.
Below are the main pros and cons of thin and thick PTFE catheter liners.
Pros of thin liners: they maximize lumen diameter, improve catheter flexibility, and minimize the overall catheter profile.
Cons of excessively thin liners: they may deform during braid application, collapse under vacuum, and experience localized wear during repeated guidewire movement.
Pros of thicker liners: they provide improved dimensional stability, and enhanced wear resistance.
Cons of thicker liners: they reduce internal lumen size, and increase shaft stiffness.
References
View full reference list.
2. Hydromer. Solving PTFE Liner Bonding Challenges in Catheters. 2026.
10. JMedtech. Reinforced Tube. 2023.
11. Technologies A. PTFE Liners: Engineering the Inner Surface of High-Performance Catheters.
12. JMedtech. PTFE Liners and Tubings. 2026; https://jmedtech.com/medical-catheter.html.
15. Technologies A. Guide Catheter Engineering: Design Principles for Vascular Navigation.
16. JMedtech. PTFE Liner Post-Processing: A Manufacturing Step or Clinical Necessity? 2023.
17. Hydromer. Ultra-Thin PTFE Liners: Enabling Next-Gen Catheter Performance. 2026.
