Medical coatings have been a notable innovation in the medical device industry over the past few decades. Devices rely on specialized coatings for enhanced performance, safety, and longevity. As such, coatings play a critical role in producing safe, functional, and high-performance medical devices.
There are a variety of medical coatings available. Different types are used based on the specific application along with the required functionality and properties needed. Among them, hydrophilic coatings have become a common choice due to their versatility.
Companies, such as Hydromer®, Inc. produce both single-step and multilayer hydrophilic medical coatings. Single-step coatings can simplify manufacturing and reduce costs. On the other hand, multilayer (multi-step) coatings may be used for complex devices. This is because they can provide enhanced performance, adhesion, and reliability. The right choice will come down to the application, requirements, and cost constraints.
In this guide we cover multilayer hydrophilic coatings in more detail. We will discuss the benefits of applying multiple layers of coatings to medical devices and the critical considerations during the application process.
Are multi-step hydrophilic coatings the right choice for your medical device?
Make sure you read this guide to the end in order to find out!
What are Multilayer Hydrophilic Coatings?
Hydrophilic coatings are a type of surface modification coating. The term “hydro” means water, and “philic” means affinity or love for. These coatings are activated in the presence of liquids and biological fluids, and become “slippery-when-wet”. They form a lubricious layer on medical devices with low friction and high wettability without the need for lubricant.
The complexity of medical procedures (and devices) continues to grow. As a result, the demand for increasingly advanced hydrophilic medical device coatings, able to provide more and more functionality is also growing. That’s where leading companies like Hydromer®, Inc. started combining different coating chemistries with advanced deposition techniques to develop complex multi-step hydrophilic coatings.
Some of the benefits of these advanced hydrophilic coatings include:
- Drug-eluting capabilities
- Antimicrobial properties
- Wettability
- Biocompatibility
- Excellent lubricity (reduced device friction)
- Low particulate
- Enhanced adhesion
- Thromboresistance to reduce blood clotting
- Durability
- Compatibility with a wide range of medical devices and materials
- Long-lasting hydrophilicity
Whereas one-step coatings contain a single layer, multilayer hydrophilic coatings include more than one. The layers include a primer layer for adhesion and multiple, distinct layers of topcoat formulations. Multiple layers are applied to the surface of medical devices in order to add multiple functionalities to the overall coating system. We discuss the multiple layers of these coatings in more detail below.
Different Layers of Multilayer Hydrophilic Medical Coatings
The different layers of multi-step medical coatings consist of hydrophilic polymers, crosslinking agents, and various additives to deliver specific properties. These layers’ functionality may vary based on the manufacturer, application, or device (catheters, guidewires, lenses, stents, etc.).
Below we discuss the most common layers of multilayer hydrophilic medical coatings. However, it should be noted that different coating systems can have different layers.
Layer 1: The Primer Layer
The substrate or medical device surface is usually made of metals, polymers, or ceramics. A primer is the first layer. It is applied directly to the medical device surface. The primer layer is helpful in ensuring proper adhesion between the substrate and the topcoat.
If the use of a primer is inappropriate, the manufacturers use surface preparation methods to ensure proper adhesion. The most common example is the plasma treatment. The methods help prevent the delamination of the coating during use.
Layer 2: Base Coat
The base or tie layer creates a stabilizing foundation for the primary or top hydrophilic coat. Its main purpose is to ensure better stability, durability, and chemical compatibility.
It is also known as the anchor layer, which is made up of crosslinked polymers and UV-curable resins.
Layer 3: Hydrophilic Top Coat
The hydrophilic top coat layer is the layer responsible for the lubricity and hydrophilicity of the multi-step coating. This layer comprises hydrophilic polymers, including polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), or polyacrylamide and can include other components.
This layer also ensures biocompatibility and helps meet stringent quality standards.
To learn more about hydrophilic coatings, click here: Hydrophilic coatings for medical devices: intro, benefits, and uses.
Layer 4: Functional Layer
The functional layer is optional. It helps device manufacturers deliver procedure or application-specific functionalities to the devices.
There are various functional layers that aim to enhance procedural safety, functionality, and device longevity. Medical device manufacturers thoroughly evaluate each one of them.
- Antimicrobial Layer: One of the most common functional layers applied to medical devices. It prevents the growth of microorganisms and bacterial colonization on the device.
- Drug-Eluting Layer: Allows the periodic release of therapeutic agents for localized and more effective drug delivery. For example, it may encapsulate anti-thrombogenic, anti-inflammatory, or antimicrobial drugs as per the application.
- Barrier Layer: Ensures the proper hydration and swelling of the top hydrophilic coat. The main purpose of this coating layer is to prevent overlubrication when the device is continuously exposed to biological fluids.
- Anti-Thrombogenic Layer: Blood clotting is the most common complication associated with the medical devices inserted or implanted into the body. An anti-thrombogenic layer reduces platelet adhesion and prevents the formation of blood clots on the surface of medical devices.
- Stimuli-Responsive Layer: Medical implants are exposed to a corrosive and dynamic biological environment. As such, they must withstand various biological triggers that can hamper their performance. So in this case, stimuli-responsive layers have proven beneficial. Such layers allow medical implants to respond to pH, temperature, light, or enzyme changes. Learn more about stimuli-responsive coatings.
Important Considerations During the Application of Multilayer Hydrophilic Medical Coatings
The successful formulation and application of multi-step coatings requires expertise as well as advanced technology. Here are just some of the things that must be considered while applying multi-step coatings to medical devices:
- Surface Preparation: Proper adhesion heavily depends upon the cleanliness and readiness of the device surface. As a result, various physical and chemical surface treatment methods may be used to remove contaminants, apply primers, and create reactive bonding sites.
- Layer Compatibility: Improper bonding or adhesion can lead to cracking, loss of lubricity, and blistering. That’s why the different layers of the multi-step coating system must strongly adhere and integrate together. This is critical for performance as well as to prevent safety issues.
- Coating Method: Applying the coating to all parts of a device is important. Also, coating thickness plays a critical role in achieving consistent lubricity across a device’s surface. It must remain the same across the entire surface to prevent friction and inconsistent performance. As such, it is important for medical device manufacturers (or their contract coating companies) to choose the most appropriate coating method (dip, spray, spin, etc.) based on the dimensions and complexity of the underlying medical device.
- Curing Method: Once the coating is applied, curing ensures proper adhesion and stabilized polymer networks. The two most popular methods are UV curing and thermal curing.
- Proper Hydration: Overlubrication causes swelling and extremely slippery surfaces. This can prevent surgeons from precisely controlling the medical devices during navigation through tortuous anatomical pathways. To avoid such inefficient device stability, manufacturers must focus on optimizing their polymer selection. A few prefer adding a barrier or control layer to regulate hydration.
Regulatory Considerations
Outside of the formulation and application considerations, regulatory compliance also needs to be taken into consideration.
All medical coating formulations must meet rigorous quality protocols outlined by regulatory bodies such as the FDA and ISO. This is critical to bringing a product to market. It is also critical in order to ensure global patient safety. Manufacturers can perform various tests to ensure their devices, including the coating system meet regulatory requirements.
Hydromer® One-Step and Multilayer Hydrophilic Coatings
Hydromer®, Inc. is a US-based hydrophilic coatings manufacturer. Our company has 40+ years of experience formulating, manufacturing, and supplying innovative, custom medical coatings. Our product portfolio includes a wide-range of custom coatings, including both one-step and multilayer hydrophilic coatings.
We understand the role of multi-layered hydrophilic coatings in today’s healthcare industry. Our highly qualified coating experts can develop custom, advanced hydrophilic coating for your product. And our contract coating services can apply your custom medical coatings effectively and affordably.
If you need to formulate a medical coating to meet your exact product and regulatory requirements then we can help. We offer both one-step and multilayer coatings as well as both thermal-cure and UV-cure hydrophilic coatings.
Get in Touch
Do you need to develop a custom multi-step, hydrophilic coating to meet your specific product requirements? If so, we can help! Our comprehensive support services allow us to help our clients overcome challenges at any stage in the product development process. Our offerings include (but are not limited to) the following:
- Research and Development (R&D) services
- Custom coatings formulation
- 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.
