Low Friction Flexible Medical Devices with Hydrophilic Coatings

Intro: Enabling a New Era of Flexibility in Medical Device Design

A major trend in the medical device industry is the increasing use of soft and flexible polymer-based devices. This is being fueled by the rapid growth of minimally invasive procedures, such as those used in heart, brain, urinary and limb operations. These procedures require medical devices that can navigate through anatomically narrow, tortuous pathways. Devices used in these procedures must also be able to accurately reach the intended destinations without causing damage to the surrounding fragile tissue.¹

Traditional devices used rigid and semi-rigid materials. These do not meet the needs of minimally invasive procedures. As a result, device manufacturers have been switching to flexible polymers. These materials allow for bending, tracking through the body, and conformation into complicated shapes of the human anatomy. The new generation of devices includes catheters, guidewires, delivery devices and microcatheters. All of these devices emphasize flexibility, ability to track through the body, and safety to the patient.^2,3

The need for flexible medical devices is growing rapidly. However, there are critical challenges that must be overcome in order to use these flexible materials safely and effectively. In this article we highlight the challenges of using flexible polymers in flexible medical devices. We also use Hydromer®, Inc’s 40+ years of coating expertise to cover why hydrophilic medical device coatings are the optimal choice for flexible polymer surface modification. 

The Hidden Challenge: Friction of Uncoated Flexible Polymer Devices

Polyurethanes (PU), PEBAX, PTFE, and nylon are flexible polymers. Specifically, they all provide the necessary flexibility for higher performance clinical applications. 

However, each of these polymers has a significant negative aspect — high coefficient of friction. 

Therefore, using these materials with uncoated surfaces leads to:

• More resistance when inserting and moving the device in the body
• Poor tracking in narrow or twisty blood vessels
• Greater risk of damaging the vessel lining and other trauma and complications
• Less control for the doctor and slower procedures

Issues caused by surface friction between device and vessel are amplified because the devices have smaller diameters and longer lengths. In neurovascular procedures, relatively small amounts of friction can create significant barriers for reaching distal lesions safely.^4-6

This is why hydrophilic medical device coatings have changed from being optional product enhancements to now being functional necessities.

Hydrophilic Medical Device Coatings Are Helping to Enable the Flexible Device Revolution

Hydrophilic surface coating technology is formulated to solve the friction problems created by devices made from polymers. Hydrophilic coatings are lubricious. They are also slippery-when-wet. When the coatings come in contact with water, they absorb it and create a slippery, hydrated layer that greatly lowers friction.

In turn, hydrophilic coatings provide several key benefits for flexible devices. Specifically, devices: 

• Move more smoothly through winding blood vessels
• Require less force to insert and travel, giving doctors better control
• Cause less damage to tissue, which improves patient safety
• Work more reliably, especially during long or complicated procedures

In short, hydrophilic coatings allow flexible polymer devices, such as hydrophilic coated catheters, to perform at their best, transforming them from just mechanically useful into high-performance medical devices.^7,8

Ability to Coat Both Inside Diameter (ID) and Outer Diameter (OD): A Critical Capability

For flexible medical device applications, lubrication is required on both the interior (ID) and exterior (OD) surfaces of devices. We discuss each of these two coatings below. 

Outer Diameter Coatings

An outer coating (OD) provides a low friction surface between the exterior of the device and body tissue. Hydrophilic OD coatings help flexible devices: 

• Navigate through catheters and microcatheters 
• Penetrate tight or obstructed lesions
• Reduce damage to the vessel wall by reducing friction with the vessel walls 

Inner Diameter Coatings

An inner coating (ID) is equally important for achieving these same benefits. ID coatings will:

• Facilitate movement of guidewires, coils, and other accessories within a lumen
• Reduce internal friction and resistance in the lumen of long/narrow catheters 
• Increase accuracy and speed for deploying the device through its catheter 

Bending and stretching of a flexible system can add to the overall resistance. Therefore, very long-lasting, hydrophilic ID coatings are critical for maintaining optimal performance of the device. 

At Hydromer® we have developed several different hydrophilic flexible coatings. These are designed to coat both the inner and outer surfaces of flexible devices. In turn, our coatings help achieve uniform lubricity throughout the entire device.⁹

Hydromer® Coatings Are Well-Suited for Flexible Devices ^10-13

Flexible devices present special demands for coating systems. Coatings need to create a lubricious, low-friction surface. Just as important is that they must also has excellent adhesion to the substrate, including while the device bends, flexes, or stretches.

Hydromer’s hydrophilic coatings are formulated to meet these critical requirements. They provide:

1. Strong adhesion to polymers: Many flexible polymers — like PU, PEBAX, PTFE, and nylon — are hard to coat because they have low surface energy or resist chemicals. Hydromer® coatings are designed to adhere reliably to these flexile materials. In turn, the coating lasts during its intended use.
2. Flexibility without cracking: Brittle coatings can crack or peel when a device flexes. Hydromer flexible coatings keep their structure during repeated bending. This is critically important for devices that must move through curved or narrow anatomy.
3. Even coverage on complex shapes: Modern devices often have long, narrow channels, and complicated shapes. Hydromer coatings, when applied using our coating application processes, can ensure consistent coating on both inside (ID) and outside (OD) surfaces, even for complex designs.
4. Long-lasting lubricity: Hydromer hydrophilic coatings provide long-lasting hydrophilicity. In other words they remain slippery when activated for a long duration. This is not just temporary or a short-lived effect. This is crucial for long procedures where long-lasting performance is needed from insertion through deployment.
5. Works with advanced device designs including multi-material devices: Devices use layered constructions and multiple materials. In turn, coatings must fit in to the overall system without hurting function. Hydromer technologies can easily adapt to these newer designs.

Polymer Selection: Flexible Plastics Supporting the Trend

The shift toward flexible devices is being driven by minimally invasive procedures. And strategic polymer selection plays a supporting role in enabling this medical device evolution. 

Below are some of the most prevalent polymers used in these types of devices: 

• PEBAX offers a balance of flexibility and strength, making it ideal for catheter shafts
• Polyurethane (PU) provides elasticity and biocompatibility
• PTFE contributes chemical resistance and baseline lubricity but still benefits from coatings
• Nylon delivers strength and push-ability

All these base materials have benefits, but none of them alone gives the very low friction needed for advanced procedures. Hydrophilic coatings fill that gap, making these polymers suitable for high-performance medical uses.^10,11

Conclusion

The shift to flexible medical devices is one the major emerging trends in today’s medical technology landscape. Advanced polymers will create the mechanical support for these devices. However, these materials do not exhibit the low friction and lubricity required for advanced, minimally invasive procedures. That is why hydrophilic coating technology is critical in developing flexible devices. Hydromer’s coating solutions will support the next generation of minimally invasive devices by decreasing friction, making them easier to navigate, and ensuring that they maintain their durability during constant motion. 

The future of medical devices is clear: they will continue to become smaller, more flexible, and more sophisticated. The new applications for flexible, polymer-based devices will include use for neurovascular treatments, structural heart interventions, and targeted drug delivery. Designing medical devices for these applications will require a new approach. Thus hydrophilic coatings are not just a useful accessory for flexible, polymer-based devices; they are critical to achieving the full benefits of these types of devices.

Get in Touch

Explore our full range of hydrophilic coatings, coating equipment, and coating services to see how our solutions can support your products and production needs. Our goal is to help customers achieve efficient, high-volume device production and develop advanced medical devices.

Contact us to learn more about Hydromer® coatingsor to schedule a consultation.

References

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3. Kim SY, Bong JH, Kim MK, et al. Minimally invasive medical catheter with highly flexible FDSOI-based integrated circuits. 2019:18.1.1-18.1.4.

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6. Bird JO, Chivers PJ. 28 – Friction. In: Bird JO, Chivers PJ, eds. Newnes Engineering and Physical Science Pocket Book. Newnes; 1993:235-237.

7. Plata M, Santander J, Zuluaga L, et al. Hydrophilic versus non-hydrophilic catheters for clean intermittent catheterization: a meta-analysis to determine their capacity in reducing urinary tract infections. World Journal of Urology. 2023/02/01 2023;41(2):491-499. doi:10.1007/s00345-022-04235-5

8. Ye L, He Y, Jingyi F, Xintian L, Lei W, Hong C. Advances in polymer hydrophilic lubricating coatings for medical catheters. Chinese Journal of Medical Instrumentation. 2021;45(1):57-61. 

9. Kazmierska KA, Ciach T. Bioactive coatings for minimally invasive medical devices: Surface modification in the service of medicine. Recent Patents on Biomedical Engineering (Discontinued). 2009;2(1):1-14. 

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