Coronary restenosis is a major challenge today. This is especially true after coronary angioplasty and stenting procedures. The rate of restenosis varies from 32% to 55% of all angioplasties. It can lead to serious health issues and even death in some cases. The most common solution to this problem is a repeat angioplasty and heart bypass surgery. Another promising strategy to prevent restenosis are drug-eluting hydrophilic coatings. These advanced medical device coatings are applied to stents and balloons during coronary interventional procedures.
In this article, we will discuss how drug-eluting hydrophilic coatings deliver antiproliferative drugs. Further, we explore how they help avoid the narrowing of coronary arteries. Last, we discuss innovative hydrophilic drug-eluting coatings developed by Hydromer®, Inc. These and similar products have revolutionized drug delivery systems and the treatment of coronary artery disease (CAD) over the last decade.
What are Drug-Eluting Hydrophilic Coatings?
Medical device coatings play a critical role in the success of medical devices and implants. This is true for devices such as drug-eluting stents (DES) and drug-coated balloons (DCB).
Drug-eluting hydrophilic coatings are specialized surface modifications added to the device surfaces. They prevent post-surgical complications such as restenosis, or the narrowing of blood vessels after surgical treatment. These coatings are capable of encapsulating active pharmaceutical ingredients. They also control the drug release kinetics (for controlled drug release).
These coatings can serve additional functions outside of just drug release. This makes them even more valuable for use on such medical devices. For instance, our custom hydrophilic coatings are “water-loving” and “slippery-when-wet”. Such coatings reduce friction and increase lubricity while also delivering therapeutic agents slowly and controllably. They also can serve as thromboresistant coatings, which reduces the adherence of blood to the surface of the device. This reduces blood clotting and related issues. They are also biocompatible and antimicrobial.
If you want to learn more about these coatings, make sure to read our comprehensive Hydrophilic Coatings Guide.
Materials Used In Drug-Eluting Hydrophilic Coatings
The right material is important for a time-controlled drug release that can balance the drug supply and absorption by the surrounding tissues.
1. Polymers
Drug-eluting hydrophilic matrix polymer coatings are made from materials like Polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and hyaluronic acid. They ensure adhesion and provide a better scaffold for drug loading. Polymeric drug-eluting systems are efficient drug-eluting carriers. These coatings:
- Provide a robust framework for controlled drug release
- Prevent degradation when in contact with the surrounding environment
Here are some of the factors affecting the drug release kinetics from the coating:
- Thickness of the polymer layer
- Dissolution or degradation of the polymer
- Breakage of covalent bonds
- Enzymatic degradation
- Permeation pressure
Hydromer has decades of experience manufacturing and supplying polymer-based, high-performance, hydrophilic medical coatings. Our coatings are biocompatible and designed to improve the efficiency and safety of our clients’ medical devices.
2. Biodegradable Materials
Drug-eluting medical devices using non-biodegradable materials may trigger inflammatory responses. These can cause in-stent restenosis (ISR).
Poly Lactic-co-glycolic acid (PLGA) and polycaprolactone (PCL) are a few of the examples of biodegradable polymers used to design drug-eluting stents. Such biodegradable polymeric matrices are becoming the kingpin of the local intravascular drug delivery system. The degradation of such materials depends upon mass-preservation equations.
3. Inorganic and Hybrid Coating Materials
Materials such as silica nanoparticles, hydroxyapatite, titanium dioxide (TiO₂), and zirconia are used to design highly stable and biocompatible drug-eluting medical devices.
These materials improve the stability of the coatings. They also improve the release kinetics of the active pharmaceuticals encapsulated on the surface of the medical devices. They are especially helpful when you are seeking robust and long-term performance.
Controlled Drug Release Mechanisms
Controlled release of the therapeutic drug dose over the desired period is absolutely critical. It determines smooth muscle cell growth and the prevention of restenosis.
Strategies have changed over time when it comes to controlling drug release from implants and interventional medical devices. In the past, strategies included polymer degradation, erosion, and dissolution of the particulate drug. Today, the most common antiproliferative drugs used in drug-eluting devices are sirolimus, everolimus, zotarolimus, and paclitaxel. Their properties, such as particle binding ability, diffusion coefficients, and mass transfer coefficients, play a crucial role in the success of the medical device.
Drugs must diffuse through the polymer matrix before they are released into the surrounding medium.
Formulation Considerations
Considerations while formulating drug-eluting coatings including:
- Solubilization dynamics of drug particles
- The rate of diffusion of the drug through the polymer matrix
- Drug recrystallization
- Drug internalization process
There are three types of polymer-based drug-eluting systems. We discuss each of them in more detail below.
1. Drug-Eluting Reservoirs
In this type of drug eluting system, the drugs are encapsulated within the polymeric membrane. The rate at which the drug is released depends upon the following factors:
- Thickness of the coating
- Permeability of the polymer membrane
- Polymer composition and molecular weight
- Solubility of enclosed drug
- Size of the drug particles
It is one of the most common strategies for delivering drugs to the surrounding medium.
2. Matrix Systems for Controlled Drug Release
In a monolithic polymer matrix system, drugs are dispersed at the molecular level or in the form of solid drug particles within the polymer network. This network distributes drugs to the surrounding medium. The drugs are released through diffusion, erosion, or dissolution of the entire matrix network.
Unlike reservoir-based drug delivery systems, it prevents burst release. This makes matrix-based drug delivery systems more efficient and reliable.
3. Conjugated Systems or Covalent Drug Conjugation
Both drug delivery systems discussed above release drugs noncovalently. Conjugate systems deliver drugs in the form of covalent conjugates. These use water-soluble and biodegradable polymers. It allows more controlled release and bioavailability.
The technique is also referred to as the covalent conjugation of drugs. It uses biodegradable polymers such as polyethylene glycol (PEG), poly lactic-co-glycolic acid (PLGA), and polysaccharides.
Applications of Hydromer® Drug-Eluting Hydrophilic Coatings
Our drug-eluting hydrophilic coatings can be applied to a variety of medical devices. They are also highly customizable and designed by our team of highly qualified Ph.D. chemists. Further, our team of regulatory experts understand the FDA, ISO, and other medical regulations worldwide. This means we can help you develop a coating to meet both your product and regulatory requirements.
Hydromer has experience incorporating our clients’ specific drug(s) or molecule(s) into custom drug-eluting, medical device coatings. If this is an area you have interest in, we can help you. Our team can help you formulate a custom drug-eluting hydrophilic coating that incorporates your specific drug or molecule.
Here are a few medical devices that can be coated with Hydromer® drug-eluting hydrophilic coatings:
- Cardiovascular Stents: As discussed in the previous sections, drug-eluting coatings are applied on cardiovascular stents to release therapeutic agents and prevent restenosis.
- Balloons: These are also known as Drug-Coated Balloons (DCBs). They minimize blood vessel reclosure by delivering antiproliferative drugs during angioplasty.
- Catheters and Guidewires: Hydrophilic coatings reduce friction and ensure smooth navigation during operational procedures. Their drug-eluting properties release anticoagulants or anti-inflammatory drugs to avoid thrombosis and infections.
- Intraocular Lenses: Ophthalmic devices such as intraocular and contact lenses are coated with anti-inflammatory or anti-glaucoma drugs to reduce post-surgical inflammation and infection.
- Wound Dressing: Drug-eluting hydrophilic coatings can be used to release antibiotics and growth factors into chronic wounds and burns. They support quick healing, promote tissue generation, and prevent infections.
Conclusion
With advancements in material science and biomedical engineering, the efficiency and effectiveness of drug delivery systems have improved significantly. At Hydromer, we aim to supply high-performance hydrophilic coatings with highly sought-after performance attributes such as:
- Drug-eluting capabilities
- Antimicrobial
- 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
Our goal is to allow clients to focus on their core strengths and help them quickly bring advanced products to market. Contact our team to learn about our wide-range of services below:
- In-house contract coating services
- Research and Development (R&D) services
- Specialized Analytical Testing
- Custom Machine Building
- Turn-key Operations
- Technology Transfer Services
- Technical consulting and support service
