Hydrophilic Coatings: What They Are and Common Uses

Hydrophilic coatings are specialized thin layers applied on the surface, thereby making the surface “water-loving.” These layers are like magnets that attract water molecules from the surroundings’ fluid. After the coating gets wet, it becomes smooth and slippery. These water-loving, smooth surfaces enhance the material properties. As such, they are proving to be exceptionally beneficial in various industries. The coatings attract and retain water molecules. This is turn creates a protective hydration layer that improves lubrication, prevents fouling, and enhances biocompatibility of the coated surfaces.

By understanding the principles and benefits of this class of coatings we can develop innovate solutions to address challenges in fields such as medicine, industry, and environmental science. In this article we will cover what hydrophilic coatings are, some of their common uses, and their many benefits.

The Chemistry of Hydrophilic Coatings: Building Blocks for Advanced Applications

Hydrophilic coatings can be formulated from various materials to achieve desired properties such as durability, biocompatibility, and resistance to environmental stress. Some of the most common materials include:

1. Polyvinylpyrrolidone (PVP):
   • PVP is widely used in water-loving coatings due to its excellent water-absorbing properties. It forms a stable, lubricious layer when hydrated.
   • Common in medical and industrial applications requiring consistent wetting and reduced friction.
2. Polyethylene Glycol (PEG):
   • Known for its biocompatibility and non-toxicity, PEG-based coatings are ideal for applications involving biological systems.
   • Used in both medical devices and sensitive industrial environments.
3. Silicone-Based Coatings:
   • Silicone can be modified to exhibit “water loving” properties, combining flexibility and water-attraction.
   • Common in applications requiring durability and heat resistance.
4. Hydrophilic Polymers with Cross-Linking Agents:
   • Cross-linked polymers enhance the mechanical strength and durability of these coatings.
   • Suitable for demanding environments such as aerospace and heavy industries.

What types of coating processes does Hydromer™ offer?

Hydromer coatings can be applied using a variety of application methods. We can apply all of these in our ISO-certified cleanroom, or alternatively, we can provide the coating material and application method to you, along with technical support.

Our application methods include Dip, Spin, Spray, Flow Coating, and our proprietary Meniscus method.

Common Substrates For Hydrophilic Coatings

Hydrophilic coatings are versatile and can be applied to a wide range of substrates, enhancing their performance. The choice of substrate often depends on the intended application. Common substrates include:

1. Metals:
   • Stainless steel, titanium, and aluminum benefit from these coatings in applications requiring corrosion resistance, lubricity, and easy cleaning properties. 
2. Plastics:
   • Common plastics such as polycarbonate, polyethylene, and PVC are frequently coated to improve their functionality in medical and industrial applications. Polyurethanes (PUs) are widely used as substrates for this type of coatings due to their favorable mechanical properties and biocompatibility. 
3. Glass:
   • Hydrophilicly coated glass can enhance anti-fogging, scratch resistance, and self-cleaning properties, making them ideal for optical and automotive industries. 
4. Ceramics:
   • Coated ceramics find use in specialized applications where thermal stability and water interaction are critical.
5. Fabrics:
   • These coatings are also applied to textiles for improved moisture management and comfort in clothing and outdoor gear. 

Substrates for Hydromer Hydrophilic Coatings

Hydromer coatings can be used on a large range of substrates. Some of these are listed below:

• Acrylic
• Aluminum
• Glass
• HDPE
• Latex and Butyl Rubbers
• Lubricants
• Mirror
• Multi-material components
• Nickel Titanium
• Nylon
• PEBAX
• PET
• Polyamides
• Polycarbonate
• Polyesters
• Polyethylene
• Polyethyleneimine (PEI)
• Polymides
• Polypropylene (B)
• Polystyrene
• Polyurethane
• PTFE
• PVC
• Silicone
• Stainless Steel
• Steel
• Teflon/PTFE
• Titanium
• And more

Common Hydrophilic Coating Applications

This class of coatings have a wide range of applications across industries. This is thanks to their unique properties. Below is an overview of where these water loving coatings are commonly used:

Medical Use

• Cardiovascular devices, Catheters and Guidewires: hydrophilicly coated medical devices improves their lubricity and reduces friction during insertion. This results in minimizing patient discomfort and tissue damage. 
• Surgical Instruments: Enhanced anti-stick properties ensure better performance during procedures. The lubricating effect gives medical practitioners superior control, enhancing procedural accuracy and reducing the risk of accidental tissue damage.
• Implantable Devices: Coated implantable devices enhance biocompatibility and reduced thrombogenicity for the implanted devices.

Industrial Use

There are a wide range of hyrophilic coatings used for anti-fog, anti-frost, and condensation control, among other things. Below are a few industrial uses for these coatings.

• Pipelines and Valves: hydrophilicly coated surfaces help in reducing drag, preventing fouling, and enhancing flow efficiency in fluid transport systems.
• Automotive Components:  Hydrophilic coatings are being used for their anti-fog capabilities on windshields and mirrors to improve visibility and safety. They are also used for automotive headlights and instrument covers and gauges.
• Optical Devices: Specialized coatings prevent fogging and dirt accumulation on lenses, goggles, face shields and more.
• Aerospace Applications: Coatings reduce ice formation on aircraft surfaces, improving safety and performance. They are also used on aerospace visors, instrument covers and gauges, and more.
• Energy Sector:  Hydrophilic coatings are being applied to solar panels and wind turbine blades to maintain efficiency and reduce environmental induced wear and tear.

Consumer Products

• Eyewear: Anti-fog and anti-scratch coatings improve user experience and durability.
• Household Items: Coated tiles and glass prevent water spots and enhance cleanliness.
• Sports Equipment: Coatings are being used on swim goggles and diving masks to prevent fogging.
• Marine: Hydromer Sea-Slide® helps enhance boat performance by reducing friction, allowing the boat to go faster while using less fuel.

Key Considerations When Selecting a Hydrophilic Coating

In order to ensure optimal performance and select a suitable hydrophilic coating for any specific substrate, it is important to consider several important factors. These factors include the chemical composition of the coating, the desired surface properties, the application, and the interaction with the substrate material. Some of these factors are discussed below:

Chemical Composition of Coating and the Specific Substrate

The selection of appropriate materials used in such coatings is very important. For instance, polyvinyl alcohol (PVA)- or polyethylene glycol (PEG)-based coatings that boast hydrophilicity and biocompatibility are suitable for biomedical applications.¹

Moreover, the mechanical properties of the substrate and the coating should also be considered for their compatibility and long-term durability.² Therefore, it is important to determine the interaction between the coating itself and the substrate. This will help to ensure long term efficacy of the coating.  

Coating Surface Properties

The rougher surface and the wettability of the coating are two significant parameters that yield a fine coating application. Hierarchical roughness in coatings would thus improve hydrophilicity and lessens the contact angle hysteresis, which is beneficial for applications requiring low friction and high water affinity.³ Therefore, surface morphology evaluation should be done primarily with regard to the effect on hydrophilicity in the selection of the coating. Custom coating formulations are helpful in this regard. 

Intended Application For the Hydrophilic Coating

The intended application of the hydrophilic plays a critical role in the selection process. For biomedical applications, apart from being hydrophilic, coating material should most likely also be biocompatible and resistant to bacterial adhesion.⁴ On the other hand, environmental applications, such as oil-water separation, may select coatings that are highly hydrophilic and oleophobic underwater to increase effective performance.⁵ Therefore, it is important to understand the specific requirement of the application to select an appropriate coating material for your application. 

Required Durability and Stability

It is important for hydrophilic coatings to show long-term stability. To prove its durability, hydrophilic coating should withstand temperature changes, exposure to various chemicals, and the ability to resist mechanical stress. Therefore, determination of hydrophilic coating stability during the intended operational environment is important for ensuring its longevity.⁶

Regulatory Compliance

Hydrophilic coatings for medical applications or other sensitive uses must comply with the applicable industrial domain-specific regulations. The regulatory bodies, such as the US Food and Drug Administration (FDA) and American Society for Testing and Materials (ASTM International), have established specific guidelines with respect to the quality and performance required in order to meet the standards. These regulations are  established to ensure that the hydrophilic coating is safe and effective.

However, being stringent in nature, these regulations may become very difficult to comply with from several consideration, including cost and know-how. Fortunately, Hydromer has in-house experts that can help guide your team along the approval process. 

Hydromer Hydrophilic Coatings

Hydromer, Inc., a leading provider of hydrophilic coatings, offers specialized solutions tailored to both medical and industrial needs.

1. Hydromer Medical Coatings:
   Our line of medical coatings improve the performance of catheters, guidewires, and other devices by providing exceptional lubricity, biocompatibility, and other key functions. Our coating solutions are also designed to meet strict regulatory requirements, ensuring approval and safe use in healthcare settings. Learn more at Hydromer Medical Coatings.
2. Hydromer Industrial Coatings:
   In industrial applications, our coatings enhance flow efficiency, reduce drag, and prevent fouling in pipelines and automotive components. Their advanced formulations deliver durability and efficiency even in extreme environments. They also help reduce fogging and frost. Explore industrial applications at Hydromer Industrial Coatings.

Conclusion

Hydrophilic coatings offer a breakthrough technology that will change the way the product has been achieved in the medical, industrial and consumer products. These 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 modern challenges, whether it’s enhancing prospects of medical devices, or streamlining industrial processes.

References:

1. Kim K, Ingole PG, Yun S, Choi W, Kim J, Lee H. Water vapor removal using CA/PEG blending materials coated hollow fiber membrane. Journal of Chemical Technology & Biotechnology. 2015/06/01 2015;90(6):1117-1123. doi:https://doi.org/10.1002/jctb.4421
2. Trantidou T, Elani Y, Parsons E, Ces O. Hydrophilic surface modification of PDMS for droplet microfluidics using a simple, quick, and robust method via PVA deposition. Microsystems & Nanoengineering. 2017/04/24 2017;3(1):16091. doi:10.1038/micronano.2016.91
3. Brown PS, Atkinson ODLA, Badyal JPS. Ultrafast Oleophobic–Hydrophilic Switching Surfaces for Antifogging, Self-Cleaning, and Oil–Water Separation. ACS Applied Materials & Interfaces. 2014/05/28 2014;6(10):7504-7511. doi:10.1021/am500882y
4. Rognoni C, Tarricone R. Healthcare resource consumption for intermittent urinary catheterisation: cost-effectiveness of hydrophilic catheters and budget impact analyses. BMJ open. Jan 17 2017;7(1):e012360. doi:10.1136/bmjopen-2016-012360
5. Chen P-C, Xu Z-K. Mineral-Coated Polymer Membranes with Superhydrophilicity and Underwater Superoleophobicity for Effective Oil/Water Separation. Scientific Reports. 2013/09/27 2013;3(1):2776. doi:10.1038/srep02776
6. Eykens L, Rose K, Dubreuil M, et al. Functionalization of a Hydrophilic Commercial Membrane Using Inorganic-Organic Polymers Coatings for Membrane Distillation. Applied Sciences. 2017;7(6). doi:10.3390/app7060637