Polymers like PEBAX and TPU are essential for modern medical devices. However, their inherent hydrophobicity creates friction and biocompatibility issues. Let’s see how hydrophilic coatings solve these polymer substrate limitations.
Polymeric materials are becoming increasingly important in the development of modern medical devices. Polymers are used extensively in many different types of devices, including minimally invasive catheters, implantable components, and wearables. At the same time, polymer materials typically undergo medical grade polymer surface modification, such as hydrophilic medical device coatings in order to be suitable for medical use.
Many polymers are used. Polyether block amide (PEBAX), nylon, polyurethane (PU), and PVC have all established themselves as foundational materials. This is primarily because they have tunable mechanical properties, high resistance to chemicals, and can be easily manufactured.1,2 In addition, polymers allow for a great deal of flexibility and design versatility.
However, they often have critical limitations when it comes to their intrinsic surface characteristics. These limitations will often inhibit their use in medical applications that require low friction, biocompatibility, and resistance to bio-fouling. Addressing these limitations has been an important challenge in the field of device engineering. And hydrophilic medical device coatings have emerged as an important enabling technology to modify polymer substrates.3,4
Advanced hydrophilic coating technologies have become a necessary part of the medical grade polymer surface modification process. They bridge the distribution of moisture and water throughout a polymer substrate. Industry leaders, such as Hydromer®, Inc offers a wide variety of hydrophilic coatings. These coatings help OEMs overcome the surface challenges of hydrophobic polymers.
In this article we use Hydromer’s 40+ years of experience to explore the surface challenges of polymer substrates. Then we look at the science behind hydrophilic surface modification and how they help OEMs overcome the challenges. Lastly, we will cover how these coatings are shaping the next generation of safe, effective, and innovative medical devices. You will discover how a well-designed coating can close the gap between polymer substrate limitations and optimal patient outcomes.
Why Hydrophobic Polymers Need Hydrophilic Medical Device Coatings 2,5,6
Most polymers used in medical devices are hydrophobic to some degree.
Why does this matter?
Hydrophobic surfaces will exhibit a relatively higher coefficient of friction as compared to tissue and blood. In a clinical setting, these two characteristics will lead to the following clinical issues:
- Increased insertion forces in vascular and neurovascular procedures
- Higher risk of endothelial trauma and inflammation
- Reduced device trackability in tortuous anatomy
- Increased potential for protein adsorption and thrombus formation
Polyether Block Amide (PEBAX) Substrates
PEBAX is considered to be a high-performing elastomer, typically utilized in any interventional device due to it’s strong flexibility and strength. PEBAX is inherently hydrophobic and moderately to highly abrasive. This can create problems with smooth navigation through vessels and increase the risk of potential irritation to the patient.
How Hydrophilic Coatings Help Solve Surface Challenges of PEBAX
The use of hydrophilic coatings can create a highly lubricated, hydrated surface. This greatly reduces the friction of the device, while improving the overall trackability, procedural management, and patient safety.
Polyurethane (PU) Substrates
PU has elastic and durable properties. These make the polymer a great choice for use in a variety of devices that will come into contact with blood. However, uncoated PU surfaces have limitations. Specifically, they are subject to the adsorption of proteins and the adhesion of platelets. Both of these realities increase the potential for thrombosis, or blood clotting, which is a serious issue.
How Hydrophilic Coatings Help Solve Surface Challenges of PEBAX
The use of antithrombogenic coatings, such as HydroThrombX® provide a hydrophilic and antithrombogenic interface between PU surfaces and body fluids. This reduces the biological interaction of PU surfaces and body fluids. As a result, the coating increases the compatibility of PU surfaces with hemocompatible surfaces. The end result is that the hydrophilic coated PU surfaces promote the performance of vascular devices.
Polyvinyl Chloride (PVC) Substrates
PVC is commonly used for tubing and catheters due to the cost savings associated with its use. However, PVC is a hydrophobic material. This results in both skin irritation through mechanical friction and biofouling during clinical application.
How Hydrophilic Coatings Help Solve Surface Challenges of
The use of hydrophilic coatings significantly improves the wettability of PVC surfaces. As a result, it reduces the coefficient of friction of the PVC device. This results in ease of insertion, improved patient comfort, and reduced skin irritation and/or encrustation of PVC surfaces over both short-term and long-term applications.
Examples of Issues Caused by Uncoated Polymers
The following are just some examples of the limitations of polymer surfaces.
- PEBAX and nylon are used extensively in catheter shafts. These polymers demonstrate excellent pushability and flexibility. However, they are poor surfaces for atraumatic navigation.
- Polyurethane and PVC are used extensively in tubing and drainage systems. Without surface modification, these polymers will likely cause discomfort to the patient due to increased complication risk.
The use of polymers in medical devices has been rising. However, if the polymer substrate is unmodified they can cause significant clinical issues. In turn, there has been a growing need to modify the surface properties of polymers without negatively impacting the bulk properties of the polymer. That is where advanced hydrophilic medical device coatings come into play.
The Role of Hydrophilic Coatings: Transforming Surface Properties of Polymer Substrates 7-10
Hydrophilic coatings are water-loving, lubricious coatings that can be used to modify the surface of polymers. They work by providing a water-attracting interface that significantly reduces friction when the coating is in a hydrated state.
When applied to a polymer substrate, these coatings provide a thin yet durable film layer that chemically binds with the polymer surface. The coating fundamentally changes how the polymer will interact with biological environments.
What do Hydrophilic Coatings Do?
Hydrophilic coating systems help overcome the challenges associated with using polymer substrates. They use advanced polymer chemistry and proprietary surface modification techniques to accomplish the following:
- Reduce the surface’s coefficients of friction significantly compared to uncoated polymers
- Enhance wettability and fluid compatibility
- Provide thromboresistance – they improve resistance to protein adsorption and platelet adhesion
- Maintain the flexibility and mechanical integrity of the underlying substrate
These enhancements provide improved surface and functional properties to devices with polymer substrates. This helps the device to meet increasingly competitive clinical performance standards.
Overcoming the Coating Adhesion Challenge on Polymer Surfaces 2,11
Obtaining durable adhesion to polymer substrates is one of the largest technical obstacles when it comes to coating polymer substrates. Many polymers, such as PEBAX and those based on polyethylene, have low surface energies and, therefore, are difficult to coat.
However, these challenges with adhesion are addressed through a combination of strategies, including:
- Surface activation techniques (e.g., plasma, corona, or chemical treatments)
- Tailored primer systems that promote interfacial bonding
- Crosslinkable coating chemistries designed for mechanical durability
These strategies achieve reliable adhesion of the coatings to the polymeric substrate of the device. This is true even when subjected to dynamic mechanical stress (bending, stretching, twisting), which are often present with interventional devices.
Hydrophilic Coatings Enhance Biocompatibility and Moisture Interaction of Polymers Substrates 12,13
Certain devices come in contact with skin or tissue over long periods of time, like urological catheters or wearable systems. These require attention to surface hydration and comfort.
Hydrophilic polymer coatings can be formulated to improve moisture interaction and reduce friction-related irritation. Hydromer hydrophilic coatings can be customized to suit specific polymer substrates such as flexible PVCs and polyurethanes. Major benefits of using hydrophilic medical device coatings for this include:
- Improved wettability and moisture retention
- Reduced tissue irritation during insertion and use
- Enhanced patient comfort in long-term applications
- Compatibility with drug incorporation for combination devices
Hydromer hydrophilic coatings have been successfully used for both critical surface performance and patient experience in many different applications.
How Hydromer® Coatings Enable the Use of Polymers in Medical Devices
1. They provide Lubricity and Low-Friction Performance 1,2,7
A critical requirement for polymer-based interventional devices is low-friction and lubrication. While the mechanical properties of both PEBAX and nylon are great, their high coefficients of friction can impede device navigation. Hydromer® hydrophilic coatings have been created to significantly reduce friction when hydrated. When exposed to water, Hydromer® hydrophilic coatings create highly lubricious hydrogels that help with smooth device insertion and navigation.
Functional benefits include:
- Greatly reduced surface friction (often by several orders of magnitude)
- Improved trackability when traversing complex blood vessels
- Less insertion force and resistance during procedures
- Enhanced control for the clinician when performing minimally invasive procedures
Hydromer® hydrophilic coatings are an excellent surface modifier for use on polymeric catheter shafts (for reducing catheter friction), guidewires, and introducer sheaths. This is because these devices require consistent lubricity, which is critical to procedural success.
2. Thromboresistance for Blood-Contacting Devices 14
Polyurethane and PVC substrates are used in many blood-contacting devices. These polymers have a high affinity to adsorb proteins and activate platelets when they come into contact with blood. This leads to thrombus formation and the associated complications that result from those thrombus formations.
Hydromer, Inc. offers a full line of anti-thrombogenic coatings. One is HydroThrombX®, Hydromer’s innovative coating system that provides a solution to the above-mentioned problems. This coating integrates antithrombogenic activity functions within a hydrophilic matrix. It helps decrease biological interactions at the interface of blood-contacting devices and their surfaces.
Functional benefits to using HydroThrombX® include:
- Decreased platelet adhesion and activation
- Decreased protein adsorption on polymer surfaces
- Improved biocompatibility of vascular and cardiovascular devices
- Potential decrease in thrombus formation and/or thrombus-related complications associated with thrombus formation for devices that are used in the blood.
HydroThrombX® is especially appropriate for blood-contacting devices such as central venous catheters and extracorporeal circuits, where it is critical to maintain the biocompatibility of their surfaces.
3. Durability Under Clinical Conditions
Medical device coatings need to offer more than just initial performance. They must be durable enough to maintain their functionality throughout the intended use of the device. Hydromer’s coating systems are designed to withstand:
- Repeated mechanical stress
- Exposure to physiological fluids
- Sterilization processes
This coatings durability is particularly critical for polymer substrates, which may undergo significant deformation during use. A well-engineered coating must flex and move with the substrate without delamination or degradation.
Critical Role of Hydrophilic Coatings in Polymer-Based Medical Device Innovation
Polymer science continues to evolve. And alongside it, new materials with enhanced mechanical and functional properties are being introduced into the medical device space. No matter the polymer type, the need for optimized surface performance remains constant.
Hydrophilic coatings will continue to play a pivotal role in:
- Enabling next-generation minimally invasive devices
- Supporting the transition toward more complex, multi-material systems
- Enhancing patient outcomes through improved device-tissue interaction
Hydromer’s continued innovation in coating chemistry and application technology positions it at the forefront of this evolution.
Conclusion
Polymers have become the dominant substrate in the medical device market. This is because they provide unparalleled levels of versatility and performance for a wide range of med tech applications. At the same time they also present concerning surface challenges if left unmodified. To address these challenges, Hydromer has developed a series of hydrophilic medical device coating systems, such as HydrUV™ UV hydrophilic coatings that act as a bridge between the material properties of polymers and their in vivo clinical performance. These coatings provide the ability to modify a wide range of polymers, creating durable, lubricious, and biocompatible dynamic medical device surfaces.
Contact our team to learn more about Hydromer® hydrophilic medical device coatings or to request samples.
References
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