Flexible medical devices have revolutionized the healthcare industry. They are able to bend, twist, flex, or stretch under normal operating conditions. They can easily navigate complex anatomical pathways. And they can maintain their performance under dynamic mechanical stresses.
However, such medical devices are complicated to coat due to their flexibility and complex geometries. In addition, conventional hydrophilic coatings applied to them can crack, lose durability, or wear off over time. As a result, these flexible devices require a specialized hydrophilic formulation to ensure excellent adhesion, durability, and performance.
In this article, we do a deep dive into Hydrophilic Flexible Coatings. We will explore their benefits as well as common applications. So if you are involved in biomedical engineering, you will want to read this article until the end to learn how you can improve the functional life of coatings applied to flexible devices.
What are Hydrophilic Coatings?
The term “hydro” means water, and “philic” means affinity or love for. As such, hydrophilic coatings are “water-attracting” surface treatments.
Hydrophilic coatings attract water molecules from their surroundings. They will absorb water and swell upon contact with water, saline solution, or bodily fluids. This activates the coating and creates a thin, highly lubricious layer on the surface of the substrate.
They are biocompatible, lubricious coatings at their core, and they are used extensively for lubricity and to reduce friction between medical devices and body tissue. However, they can be custom-formulated with various useful properties to serve different functions. These include but are not limited to thromboresistance, antimicrobial properties that help reduce infections, and more.
Customized hydrophilic coatings are used across extensive applications in diverse industries. For example, Hydromer®, Inc. has 40+ years of experience serving medical, optical, automotive, marine, aerospace, and other industries.
Conventional vs. Hydrophilic Coatings For Flexible Devices
Hydrophilic coatings’ wettable, low-friction design has significantly evolved over the past four decades. When these coatings were first introduced, their main goal was to reduce friction and create a smooth surface on medical devices, such as catheters and guidewires. As mentioned above, they have evolved significantly over time to become much more advanced.
Limitations of Conventional Hydrophilic Coatings
Hydrophilic coatings have come a long way. Thanks to advanced technology, they can lower friction forces by up to 98% compared to uncoated device surfaces.
Their traditional or standard design performs well on rigid substrates such as glass, metal, or hard plastics. But on soft, elastic polymer-based substrates, hydrophilic coatings crack and lose lubricity. This happens particularly when the underlying substrate bends, twists, or stretches. And unfortunately, many medical devices require flexibility in some form or fashion.
In other words, traditional hydrophilic coatings are too brittle and rigid for flexible medical devices.
Hydrophilic Coatings that are Flexible
Flexible hydrophilic coatings are a specialized class of hydrophilic formulations. They are designed to maintain their durability and performance even when the flexible medical devices are subjected to dynamic mechanical stress.
Consider a vascular catheter, which travels through tortuous blood vessels to deliver fluids, medications, and more. It experiences various mechanical forces that bend, squeeze, or twist the catheter. In this case, specialized flexible hydrophilic coatings are proven to be useful. Their cross-linked polymeric design can stretch and move in response to the shape and movement changes in these catheters.
Note that they do not change shape independently; instead, they adapt to or respond to the shape changes of the underlying substrate.
Common Polymer Chemistries Behind Flexible Hydrophilic Medical Coatings
Flexible medical devices are made up of thermoelastic elastomers (TPEs), Pebax®, polyurethanes (PU), fluoropolymers (PTFE), polyethylene (PE), and more. These devices are largely polymer-based. Achieving uniform coating adhesion on such device substrates is difficult, but it is possible.
Here are the polymer chemistries that make flexible hydrophilic coatings both hydrophilic and elastic:
- Polyurethane-Based Hydrogels: These are designed by blending hydrophilic polymers with polyurethane chains. Polyurethane offers excellent flexibility and mechanical strength.
- PEGylated Elastomers: The poly(ethyleneglycol) is extremely hydrophilic in nature. It must be combined with elastomers, such as polyurethane and Pebax. This is done through copolymerization or grafting for rubber-like stretch and flexibility.
- Silicone-Based Polymers: Silicone polymers are highly flexible but hydrophobic. They repel water molecules instead of attracting them. However, they can be combined with hydrophilic polymers, such as PEG to provide flexibility and lubricity.
- Polyzwitterion-based Polymers: Poly(carboxybetaine) and poly(sulfobetaine) are examples of zwitterionic polymers. They have both positively and negatively charged groups within the same repeating unit. The hydrophilic coatings designed using these polymers are highly hydrophilic as well as flexible.
Benefits of Flexible Coatings that are Hydrophilic
Below we quickly explore the benefits of custom-formulated hydrophilic coatings compared to other coatings for flexible medical devices.
- Crack Resistance: The main problems associated with coatings used on flexible medical devices are cracking, peeling, or delaminating. Flexible hydrophilic coatings are able to stretch, bend, and twist in response to shape changes and/or movements in the underlying substrate.
- Uniform Coating: Medical devices made of flexible polymers have low surface energy. This causes issues with conventional coatings adhering to the surface of these devices. Advanced, flexible hydrophilic coatings are able to form stronger bonds with polymer-based substrates. Such coatings can uniformly coat micro-scale, coiled, braided, or highly elongated medical devices. They are fully compatible with medical devices that have complex device geometries.
- Enhanced Lubricity: Hydrophilic formulations offer superior lubricity when compared to other medical device coatings. As mentioned above, this is because they absorb water. This creates a thin, highly lubricious layer on the device’s surface. This low-friction surface allows smooth and safe insertion of devices into the body. It also provides better navigation of devices, such as catheters and guidewires, through tortuous pathways. Learn more about lubricious coatings.
- Reduced Trauma: Flexible hydrophilic coatings maintain their performance or lubricity without cracking. This eliminates the risk of frictional trauma to delicate tissues and blood vessels in the body.
At Hydromer®, Inc. we offer custom, multifunctional, flexible hydrophilic coatings to meet the needs of complex devices. These coatings can be formulated with highly sought-after performance attributes, such as:
- Drug-eluting capabilities
- Antimicrobial properties
- Wettability
- Biocompatibility
- Low particulate
- Thromboresistance (reduces blood clotting)
- Compatibility with a wide range of medical devices
- Long-lasting hydrophilicity
To read more about their multifunctional hydrophilic coatings, click Hydrophilic Coatings for Medical Devices: Intro, Benefits & Uses.
Devices That Benefit from Flexible Coatings
What devices use hydrophilic flexible coatings? Devices and implants that experience continuous bending, flexing, twisting, and stretching.
Here is a quick list of polymeric medical devices that are coated with flexible hydrophilic coatings. These coatings provide enhanced reliability and safety during minimally invasive procedures:
- Catheters: These are one of the most used flexible medical devices. They are passed through tortuous vascular channels. Nearly all types of medical catheters must be coated with flexible hydrophilic catheter coatings for enhanced performance.
- Guidewires: These are used to guide catheters or other medical devices to the target location. Flexible hydrophilic coatings for guidewires ensure they smoothly navigate the complex anatomical pathways without cracking or delaminating.
- Balloons: These coatings are applied to angioplasty or dilatation balloons to prevent vessel trauma during inflation or expansion and significantly improve trackability during navigation.
- Endotracheal Tubes (ETTs): These tubes usually remain in place for hours or even days. They are bent or flexed during patient movement, neck rotation, and other activities. As a result they must be coated with flexible hydrophilic formulations to ensure reliability.
- Stents: Both coronary and neurovascular stents help restore blood flow by keeping the vessel open. They are subjected to continuous flexing, pulsating blood flow, and shear stress. Flexible hydrophilic coatings offer excellent elasticity and prevent cracking.
- Scopes: These are diagnostic devices used in gastrointestinal, bronchoscopy, urology, gynecology, and ENT procedures. They have to navigate through the torturous pathways. Hydrophilic scope coatings that are flexible help surgeons drastically improve patient comfort during various diagnostic procedures using medical scopes. They prevent bending, twisting, and flexing of scopes.
Hydromer® Flexible Hydrophilic Coatings Manufacturer
Hydromer®, Inc. is a US-based manufacturer of hydrophilic coatings. Our company has 40+ years of experience formulating, manufacturing, and supplying innovative lubricious hydrophilic coatings for medical devices.
We understand the role of flexible medical devices in today’s healthcare industry. These devices ensure safe navigation through complex anatomical pathways and enable minimally invasive procedures. Our company develops custom, advanced hydrophilic coating formulas that can withstand bending, twisting, flexing, and stretching.
All of our hydrophilic medical coatings are customizable. This means we can formulate a coating to meet your exact product and regulatory requirements. We offer both thermal-cure and UV-cure hydrophilic coatings.
Need to Develop a Custom Hydrophilic Coating Solution?
Do you need to develop a custom medical coating to meet your medical device requirements? If so, our team of coating experts can help regardless of your stage in the product development process.
Yes we are a manufacturer and supplier of advanced, reliable hydrophilic coating solutions. But what sets us apart from other coating manufacturers is our extensive list of support services. We can assist you throughout the entire product development and lifecycle. Our contract services include:
- Research and Development (R&D) services
- Contract coating services
- Worldwide supply of high-quality medical coatings
- Specialized Analytical Testing
- Custom Machine Building
- Turn-key Operations
- Technology Transfer Services
- Technical consulting and support services
Contact our team of experts today to learn more about our custom coatings and services.
