Surface treatment is essential for enhancing the biocompatibility, performance, and reliability of medical devices. Medical surface treatments use physical, chemical, and coating-based methods to modify a device’s natural surface properties. All of these methods can easily be applied to the outer surface of medical devices. But when it comes to coating the inner diameter (the inner surface), things get incredibly complicated.
Medical devices are becoming more sophisticated and intricate than ever before. That is because they deliver greater functionality, safety, and value in patient care. However, as complexity increases, modifying the surface properties of these medical devices becomes increasingly challenging. And modifying the inner diameter of devices is especially complex. Metal and ceramic coatings are difficult to apply uniformly inside narrow lumens due to their deposition requirements. As such, only polymer-based, inner diameter coatings are practical for the inner surfaces of medical devices.
In this article, we will discuss the use of hydrophilic inner diameter coatings for coating the inner surface of medical devices. Our goal is to understand why hydrophilic coatings are the best choice to uniformly coat narrow lumens and complex geometries of modern medical devices. We also explore the benefits of these inner coatings for this use. You will want to make sure you read until the end!
Key Challenges in Coating the Inner Surfaces of Medical Devices
There are multiple challenges associated with inner surface coatings. These have to do with achieving a uniform, well-adhered coating on the inner surface of medical devices having complex geometries. Some of the challenges include:
- Uniformity: The most traditional coating methods, including spin and spray coating, lead to uneven thickness and flaking. It is mainly due to gravity and capillary action.
- Limited Accessibility: There are a few devices, such as microcatheters, whose diameters can be under 1 mm. Things get even more complicated when these medical devices have complex shapes. These include bends, junctions, or variable cross-sections.
- Poor Adhesion: Medical devices with varying geometries have different inner surface energies compared to the exterior. This can lead to poor adhesion.
- Process Limitation: Not all surface modification methods are suitable for coating the inner surfaces (lumens) of medical devices. For example, the dip coating method causes pooling and bubbles in narrow lumens.
- Improper Flow Dynamics: Even a micrometre-thick bump or ridge can drastically reduce the internal space available for fluid flow. That’s why it is crucial to ensure that the coating is uniform and does not alter the flow dynamics.
- Safety (PFAS-Free): Modern inner diameter coatings must be engineered without PFAS (Per- and Polyfluoroalkyl Substances). Hydromer® Hydrophilic Coatings are designed using biocompatible coating polymers. These include polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and Polyurethane (PU). These coatings are safe and offer excellent lubricity and durability compared to fluorinated additives.
Hydrophilic Coatings For Inner Diameter of Devices
The term “hydro” means water, and “philic” means affinity or love for. As such, hydrophilic coatings modify medical device surfaces to be “water-loving”. The coating attracts water molecules from the surrounding environment. And they are activated in the presence of moisture, such as bodily fluids. Once activated they create thin, highly lubricious layers on the surfaces of medical devices. Because of this, hydrophilic coatings are also known as the “slippery-when-wet” surface modifications.
At their core, hydrophilic coatings are lubricious coatings. They are used to reduce the coefficient of friction between the medical device surface and body tissues. However, advanced coatings, such as Hydromer® hydrophilic coatings can be custom-formulated to possess other helpful properties. Additional properties/functionalities include:
- Thromboresistance
- High wettability
- Antimicrobial
- Drug-eluting capabilities
- Biocompatibility
- Low particulate
- Enhanced adhesion
- High durability
Click here to learn more about these multifunctional hydrophilic coatings: Hydrophilic Coatings for Medical Devices: Intro, Benefits & Uses.
Benefits of Applying Hydrophilic Coatings to the Inner Surface of Medical Devices
Hydrophilic coatings are applied to the inner surface of medical tubes for the following purposes:
1. Improved Fluid Flow
Hydrophilic coatings significantly reduce the drag on moving fluid inside devices. They do this by creating a lubricious layer on the medical device lumen (inner diameter). As such, biological fluids can easily pass through with less resistance and pressure drop.
These coatings also keep the inner surface free from proteins, platelets, and debris. It prevents flow separation and turbulence that can lead to chaotic movement.
2. Enhanced Lubricity (Friction Reduction)
Hydrophilic coatings are extremely lubricious. They are applied to the inner diameter (ID) of medical devices, such as an IOL (Intraocular Lens) injector, syringe, tubes, etc. They help ensure smooth delivery, which helps improve navigation and trackability, even in tortuous pathways.
Such lubricious coatings drastically reduce the friction between the cartridge wall and the intraocular (IOL) or artificial lens. This helps prevent deformation of the artificial lens during cataract surgery. Thanks to these coatings, surgeons can easily repair cataracts by inserting artificial lenses with less pressure.
Additionally, when hydrophilic coatings are applied to the guiding catheter lumen the slippery passage ensures that guidewires, balloons, or other medical instruments can glide through smoothly.
Hydrophilic coatings are extremely lubricious while being highly flexible, and durable.
3. Prevents Thrombosis
Thrombosis (blood clotting) is a major complication associated with the vascular devices or implants. It can be life-threatening. Inner diameter hydrophilic coatings help prevent this.
Hydrophilic coatings are applied to the inner surface (lumen) of cardiovascular devices, such as stents and vascular grafts. They create a thin, highly lubricious layer that platelets and clotting proteins can not adhere to. This helps prevent protein adsorption and thrombosis.
4. Drug-Eluting Capabilities
Drug-eluting hydrophilic formulations are a specialized class of medical coatings. They can encapsulate and deliver active pharmaceutical agents over a set period. Their main purpose is to ensure localized drug delivery for enhanced patient care.
In simple words, such coatings are able to release drugs into the blood or fluid flowing through the lumen. They can prevent both thrombosis (blood clot formation ) and restenosis (narrowing of blood vessels).
5. Enhanced Biocompatibility
Medical devices must not harm the surrounding tissues and biological fluids. They need to perform their intended functions without causing any trauma to patients.
The lubricious layer created by biocompatible hydrophilic coatings mimics the body’s hydrated tissues. As a result, the patient’s body does not treat the medical devices as a foreign object. It drastically reduces the risk of inflammation.
6. Reduced Risk of Infections
Hydrophilic coatings can be custom-formulated with antimicrobial properties. Such coatings prevent microbial growth and bacterial colonization. Additionally, the slippery, lubricious layer forms a physical barrier. This barrier makes it difficult for bacteria to adhere to the inner surface of medical devices, such as catheters and stents. As a result, hydrophilic inner diameter coatings can help reduce healthcare-associated infections (HAIs).
Medical Devices Requiring Inner Surface Coatings
There are many medical devices whose narrow lumens or hollow channels must be coated to prevent high friction, thrombosis (blood clot formation), biofilm buildup, and more.
However, as we discussed earlier, applying medical coatings to the inner surface of medical devices is a complex task. It takes specialized coating equipment and techniques, such as those used by Hydromer, Inc. to successfully coat these areas.
Here is a quick list of medical devices that may benefit from inner diameter hydrophilic coatings:
- Catheters: Catheters are used for a variety of purposes across various types of medical procedures. Inner diameter hydrophilic coatings enable the smooth, uninterrupted passage for fluids, medications, blood, and medical instruments, such as guidewires. Hydrophilic catheter coatings can be applied to the inner diameter of microcatheters, guiding catheters, aspiration catheters, and diagnostic catheters.
- Stents: The inner surface of nearly all types of stents is coated with hydrophilic formulations. These include ureteral and vascular stents. The coatings ensure the smooth flow of biological fluids, such as urine and blood.
- Feeding Tubes: Hydrophilic coatings ensure uninterrupted delivery of liquid nutrition and medication directly into the gastrointestinal tract (stomach or digestive system). It significantly reduces clogs, slowing, or backpressure of the liquid.
- Endotracheal Tubes: Mucus and other fluids can adhere to the inner walls of the ETT (endotracheal tube). It may narrow the inner diameter of the tube, which leads to increased breathing resistance. Hydrophilic coatings create a lubricious barrier on the inner surface of ETTs. This layer prevents the sticking of mucus and bacteria (which can cause ventilator-associated pneumonia).
- Vascular Grafts: Medical devices that are in contact with the blood can trigger clot formation. Hydrophilic coatings ensure smooth and safe blood flow through vascular grafts. It discourages unwanted deposits that can lead to life-threatening situations.
Hydromer® Inner Diameter Hydrophilic Coatings
Hydromer®, Inc. manufactures and supplies custom medical device coatings. With 40+ years of experience we understand the challenges of coating the narrow inner surfaces of medical devices, such as catheters and stents. Conventional coatings and coating application methods generally fail in this area. But Hydromer’s proprietary advanced, polymer-based hydrophilic coatings are designed specifically for the inner surfaces of these medical devices.
We use high-tech methods to apply and cure our hydrophilic coatings. The result is a uniform and effective coating that is highly lubricious, flexible, and durable.
All of our coatings can be custom formulated to meet your device’s specific performance and regulatory requirements.
So if you need a custom medical device coating our experts can help. Our thorough but easy process allows you to focus on your core strengths while we help you quickly bring your advanced medical products to market. From R&D to contract coating and technology transfer our coating services provide unmatched support.
Let Us Develop Your Custom Inner Diameter Coating
Do you need to develop a custom medical coating to meet your medical device requirements? If so, we can help regardless of what stage you are at in the product development process.
But what sets us apart from other coating manufacturers is the long list of support services we offer.
- Contract 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.
