Hydrophilic Coatings For Medical Device Substrates

Modern medical devices require reliable, high-performance surface coatings that work with a wide range of substrates (materials). There is a growing need for less invasive medical devices that cause less trauma, perform better, and are safe for the body. Medical device manufacturers need coatings that meet stringent product and regulatory requirements. They also need coatings that that work well with many different substrates. 

Hydromer® offers both UV and thermal cure hydrophilic medical coatings. These solutions are designed to provide strong adhesion and long-lasting lubrication across a wide range of substrates. These substrates range from polymers like Nylon and PEBAX to metals like NiTi alloys and stainless steel. 

In this article we focus on how Hydromer hydrophilic coatings can be used as surface modifications for many different materials used in medical devices. We explore why a coating’s ability to coat multiple substrates is important. And we look at why being able to choose between UV and thermal hydrophilic coatings is important depending on the device.

What is a Medical Device Substrate?

A substrate is the material (the surface) which a medical coating is applied to. In other words, it is the material being coated.

Medical devices may have a single substrate made made from a single material. More likely, they have multiple surfaces that need coated. And these surfaces are typically made from multiple materials.

Common materials used in medical devices vary widely. They include materials ranging from polymers like Nylon and PEBAX to metals like stainless steel and alloys and glass.

In turn, medical device coatings need to be compatible with a wide range of materials. These range from a wide range of different polymers to metal substrates, and glass medical device substrates as well. This is important so they adhere and perform properly.

Finding a coating that works effectively with one or multiple substrates is a key challenge in biomedical engineering. Not every coating works with every substrate. Working with a custom, medical coatings manufacturer, such as Hydromer®, Inc. can simplify the process. Our team can formulate a surface coating that works for your specific device and meets your specific product requirements.

What are Hydrophilic Medical Device Coatings? 

Hydrophilic coatings are thin, surface treatment layers added to medical devices like catheters, stents, and implants. These lubricious coatings modify the surface properties of the substrate. For example, they can increase the wettability of medical devices and help them interact better with the body. 

Some important functions of hydrophilic coatings include:

• Less friction: They help medical devices move smoothly, which creates less irritation to the body
• Increased safety: Lowers the risk of immune response and thrombosis
• Higher durability: Hydrophilic coatings can help increase the durability (life) of medical devices
• Reduce the chance of infections: Some hydrophilic coatings incorporate antimicrobial properties, which can help reduce infections
• Help cells grow: Advanced bioactive coatings can promote tissue growth. This property is important for wound healing, cellular attachment, and more  

If you want to explore these coatings in more depth, make sure to read our guide on hydrophilic coatings for medical devices: uses and benefits. 

Medical Device Substrates Vary Widely: Coatings Compatibility is Critical

The design of catheters, guidewires, stents, and other medical devices continues to change. Material science is ever evolving. Today, medical devices are engineered using many different materials. Different parts of a device can be made from a variety of materials. Each material has its own surface energy, chemical makeup, and mechanical characteristics. 

Because of this, medical device coatings need to be able to adhere properly and work effectively on a wide range of surface. The ability of coatings to adhere to many substrates greatly simplifies the process and improves performance. For instance, Hydromer® hydrophilic medical coatings work across a range of soft thermoplastics like TPU to hard polymers like PC, or even to chemically resistant materials like PP.

In addition, how the medical coating is cured also plays a role when choosing the correct coating solution for a device. That is what we discuss in more detail below. 

The Role of Coating Curing Method and Substrate Compatibility

The curing method of a specific medical device coating also has affects on substrate compatibility. For instance, some thermal cure coatings are not suitable for certain substrates. And on the flip side some UV cure coatings are not ideal for other substrates. 

Having a coating supplier that offers both UV and thermal cure hydrophilic medical coatings is helpful in this regard. 

Two popular curing methods for medical device coatings are UV-curable coatings and thermally cured (thermal cure) coatings.

Both curing methods can be used to cure hydrophilic coatings and create hydrophilic surfaces. But the two methods have important differences between them. One of the most important differences in relation to this topic is substrate compatibility. Specifically, some coatings work better with certain materials than others.

Comparing UV vs Thermal Cure Coatings: Which is Best for Different Medical Device Substrates?

Below is a quick run-down of the differences between these two curing methods used to cure hydrophilic medical coatings. We focus specifically on how the curing methods affect suitability with substrates. 

Which coating type is right for your product? Make sure to read our full guide on UV vs Thermal Cure Coatings. 

1. Curing Mechanism: UV vs Thermal Cure

• UV Coatings: Curing is initiated by exposure to ultraviolet light (typically UV-A). The polymer matrix cross-links rapidly through photopolymerization, curing the coating quickly, typically within 2-10 minutes depending on the system.
• Thermal Coatings: Heat is used to drive evaporation or chemical curing reactions, often requiring oven temperatures ranging from 50-100°C and at least 30-90 minutes of exposure.

2. Substrate Sensitivity: Certain Substrates are Better Suited for one vs Another

• UV Coatings: UV medical coatings cure at room temperature. This makes them a good fit for heat-sensitive substrates like TPU, PETG, or PEBAX that can deform or degrade under heat. 
• Thermal Coatings: Require elevated temperatures to cure the coatings. Suitable for some substrates, but has the potential to damage delicate polymers or induce warping and color shifts.

3. Durability and Coating Performance

• UV Coatings: Offer excellent crosslink density, abrasion resistance, and consistent lubricity when formulated, applied and cured properly.
• Thermal Coatings: Can achieve comparable mechanical properties and performance when formulated, applied and cured properly.

Below is a useful table comparing the two curing methods.

Criteria	UV-Curable Coatings	Thermal Coatings
Curing Mechanism	Photopolymerization via UV-A light (typically 320–400 nm)	Heat-driven chemical reaction or solvent evaporation
Cure Time	Typically within within 2-10 minutes depending on the system	At least 30-90 minutes of exposure
Curing Temperature	Room temperature (ambient)	Oven temperatures ranging from 50-100°C
Substrate Compatibility	Excellent for heat-sensitive materials (e.g., TPU, PEBAX, PETG)	Risk of deformation or degradation on thermoplastics
Coating Durability	High crosslink density; excellent abrasion and wear resistance	Good, but may vary with oven uniformity and solvent control

Below we explore how UV hydrophilic medical coatings work with common substrates used for medical devices. 

UV Curable Hydrophilic Coatings: Suitable Substrates⁵

Hydromer® UV curable hydrophilic medical coatings are suitable for use on a wide range of substrates. Below we cover some common medical device materials and the benefits of our UV hydrophilic coatings when used on these materials. 

1.Nylon (Polyamide)¹ 

• Enhanced Adhesion via Surface Treatment: UV irradiation improves the wettability and bonding strength of polyamide-based composites by introducing polar functional groups. 
• Rapid, Low-Heat Processing: UV cure hydrophilic coatings offer fast processing with minimal heat. This is important for preserving the dimensional stability of nylon components.
• Improved Chemical and Wear Resistance: UV-cured hydrophilic coatings enhance the chemical and abrasion resistance of nylon surfaces, beneficial for applications like catheters and tubing.

2. Thermoplastic Polyurethane (TPU) ²

• Preservation of Flexibility: UV curing maintains TPU’s flexibility, essential for wearable and flexible medical devices.
• Improved Mechanical Properties: UV curing can enhance tensile strength and elongation at the break of TPU composites, even after UV aging.

3. Polyethylene Terephthalate Glycol (PETG)³ 

• Low-Temperature Processing: UV curing avoids heat-related deformation, making it suitable for PETG’s low thermal tolerance.
• High-Gloss, Abrasion-Resistant Finishes: UV-cured coatings provide PETG with glossy and durable surfaces, ideal for clear packaging and medical containers.
• Maintained Optical Clarity: UV curing preserves the optical clarity of PETG, essential for applications requiring transparency.

4. Polyether Block Amide (PEBAX)⁴ 

• Retention of Elastic Properties: UV curing maintains PEBAX’s elasticity and mechanical properties, crucial for flexible medical devices.
• Enhanced Chemical Resistance: UV-cured coatings improve the chemical resistance of PEBAX, beneficial for catheters and tubing.
• Surface Energy Modification: UV curing can tailor the surface energy of PEBAX, improving bonding or lubricity as needed.

5. Polycarbonate (PC)⁵ 

• Improved Adhesion via Surface Activation: UV irradiation generates oxygen-containing functional groups on PC surfaces, enhancing adhesion to coatings. 
• Enhanced Scratch Resistance and Optical Clarity: UV-cured coatings provide PC with improved scratch resistance and maintain optical clarity, important for medical and consumer applications.

6. Polypropylene (PP)⁶ 

• Durable, Chemically Resistant Coatings: UV curing provides PP with coatings that resist chemicals, suitable for disposable medical devices.
• Rapid Processing: UV curing enables fast production cycles, reducing energy usage and production time.

Hydrophilic Thermal Cure Coatings: Suitable Substrates

Hydromer® thermal curable hydrophilic medical coatings are also suitable for use on a wide range of substrates. Below are some common medical device materials and the benefits of our thermal cure hydrophilic coatings when used on these materials. 

1. Nylon (Polyamide)⁷

• Enhanced adhesion: Thermal curing promotes better bonding due to the presence of polar amide groups in nylon, facilitating interactions with hydrophilic coatings. 
• Improved durability: Heat treatment reduces residual solvents, enhancing the longevity and performance of the coating. 

2. Thermoplastic Polyurethane (TPU)⁸

• Stronger mechanical bonding: Thermal curing facilitates deeper polymer interpenetration, resulting in enhanced mechanical adhesion. 
• Retained elasticity: The curing process maintains TPU’s inherent flexibility while improving coating adhesion. 
• Increased hydrolytic stability: Thermal curing enhances the resistance of TPU coatings to hydrolytic degradation, crucial for applications in moist environments. 

3. Polyethylene Terephthalate Glycol (PETG)⁹ 

• Strong bonding: Thermal curing enables robust covalent or hydrogen bonding with glycol-modified PET surfaces. 
• Enhanced durability: The thermal process stabilizes the hydrophilic coating structure, reducing risks of cracking or delamination under stress. 

4. Polyether Block Amide (PEBAX)^10,11

• Improved chemical anchoring: Thermal curing enhances bonding with both polyamide and polyether segments in PEBAX. 
• Maintained flexibility: The process ensures that the coating remains flexible without compromising adhesion. 
• Uniform film formation: Thermal curing promotes consistent coating application, essential for medical devices requiring uniform lubricity. 

5. Polycarbonate (PC)¹²

• Enhanced adhesion: Thermal curing improves coating adhesion by promoting interactions with polar functional groups on PC surfaces. 
• Increased resistance to stress: The process enhances PC’s resistance to crazing and stress cracking under thermal and mechanical stress. 

6. Polypropylene (PP)¹²

• Enhanced bonding strength: The process increases the durability of coatings on PP, despite its inherent hydrophobicity. 
• Improved performance: Thermal crosslinking boosts the long-term performance of coatings in hydrophobic environments. 

7. Metallic (Metal) Substrates^13-16

• Enhanced Mechanical Properties: Thermal curing improves abrasion resistance and functional properties in coatings applied to stainless steel substrates. 
• Improved Adhesion with Conversion Coatings: Thermal curing enhances the adhesion of organic coatings to aluminum and titanium substrates, leading to better durability. 

Conclusion: The Versatility of Hydromer® Hydrophilic Medical Coatings

Hydrophilic medical coatings enable new realms of innovation and efficiency by lowering friction, improving durability, and offering unique functional advantages. Hydrophilic coatings are an essential solution to the challenges faced by medical device manufacturers. Hydromer® Medical Device Coatings are versatile and work across many types of medical-grade materials. Whether you need to coat flexible plastics like TPU and PEBAX or tougher materials like PETG and PC, Hydromer has a coating solution to meet your product requirements.

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