Parylene is the most bio-compatible conformal coating currently available. Its chemical properties make it a natural for use in medical and biological applications. In addition, some of its general benefits also make it particularly valuable in healthcare applications. Finally, parylene also enjoys a stringent USP Class VI bio-compatibility certification.
Parylene's Chemistry and Capabilities
One of parylene's key benefits for biological applications is that it is chemically inert. Just about anything that it would encounter inside a body would have no impact on it. Acids, bases, salts and organic chemicals have essentially no ability to break it down.
It is also hydrophobic, making it impervious to water. This means that it is a powerful tool for sealing items against bodily fluids.
The parylene coating film is colorless and odorless, eliminating an additional source of irritation. Furthermore, because it requires no catalysts or initiators to be vaporized, deposited or cured, it also has no impurities that could eliminate its unique benefits.
Physical Characteristics of Parylene
More than being chemically bio-compatible, parylene is also a powerful tool based on its physical attributes. From its strength to its optimized-for-biological-applications thermal capabilities, it is structured for implantability.
Parylene's unique vapor-based method of deposition means that it provides the best possible conformal coating. It coats anything that air can touch. This means that it generates a coating not just on top of components, but also under them. It can even coat inside an item if it has even a microscopic opening to the air. While this can be challenging for some applications, in biological settings, this is a desirable capability. Adding to its desirability, parylene coats evenly and without any pinholes.
Typically, discussions of parylene's thermal endurance focus on its ability to withstand temperatures of up to 80 degrees Celsius for continuous periods. However, biological applications typically involve contact with lower temperatures. Testing has shown that a 37 degrees C -- normal body temperature -- parylene is stable for at least 20 years. At the same type, parylene can also withstand high pressures and even radioactivity, making it an excellent coating for items that need to go through medical-grade sterilization procedures.
Parylene forms a strong coating that is also flexible. This means that in some applications -- like stents -- it can add a small degree of needed reinforcement to the component. In addition, it also forms an extremely smooth coating. In fact, it has lubricity that is roughly comparable to that of teflon. This means that parylene coated items are likely to be easier to insert and to cause less irritation and discomfort while they are implanted.
The USP Class VI Standard
Parylene isn't just bio-compatible because of its structure and chemistry. It is also bio-compatible because The United States Pharmacopeia (USP) has certified it to be. Furthermore, it meets the USP's highest standards for bio-compatibility -- the Class VI standard.
The USP Class VI standard uses three broad types of testing to determine if a given plastic is truly bio-compatible. First, the plastic is mixed with a carrier and injected into a subject -- usually a test animal. Typically, the plastic is mixed with sodium chloride and alcohol saline and injected intravenously as well as being mixed with vegetable oil and with polyethylene glycol and injected into a body cavity. The animal is tracked for three days to ensure that it does not suffer harm or die.
The second test involves intracutaneous injection of the item in each of the four carriers into an animal. The animal is then monitored for up to 72 hours. This test shows whether or not it is a local irritant.
Finally, strips of the material are surgically implanted into living muscle tissue. The animal is then surveyed after five to seven days to see if it has a reaction to the compound.
Parylene has been through this stringent process and earned its USP Class VI certification. In addition, over a period of more than 40 years, it has proven its ability to withstand biological applications with excellent performance and excellent results for the patients benefiting from parylene-coated medical devices.
Over a period of decades, parylene has proven itself to be the best option for coating medical devices. From simple items like coated syringes all of the way up to coated stents, implantable devices and surgical equipment, parylene saves lives and improves outcomes.