According to the American Diabetes Association, more than 29 million people have been diagnosed with diabetes in the United States alone, and an additional person is diagnosed every 23 seconds. As the disease has turned into an epidemic, medical manufacturers have developed numerous devices to manage both Type I and Type II diabetes. Over the years, these devices have become more sophisticated, using more advanced technologies with the goal of providing more effective, fail-safe, and painless diabetes management.
Diabetes care is most commonly accomplished by a finger-prick test multiple times a day and, when needed, insulin delivery is completed via a simple syringe. As new monitoring and delivery systems become available (e.g., small wearable devices with wireless receivers, implantable monitoring devices, cloud-based data storage, etc.), they must continue to meet the standards of safety, effectiveness, and reliability — lives often depend on it. To ensure this high reliability and safety for patients, the industry often relies upon conformal coatings to provide the protection that today's advanced devices and components need.
Why Device Protection Is Critical
Any medical device that comes into contact with the human body — via skin contact or implantation — must be biocompatible and biostable. These requirements, in and of themselves, can drive designers to use a conformal coating. However, device protection goes much deeper than simply ensuring surface biocompatibility.
Depending on the device and its use, there can be many reasons to protect components. Needles, for example, may require a coating to ensure biocompatibility, but they also may benefit from dry-film lubricity characteristics (low coefficient of friction) to enable their smooth movement against tissue during insertion and removal. With the growth in communications and monitoring devices, connected directly or remotely to the body, the use of high-tech electronics, sensors, transducers, and batteries has dramatically increased.
Meanwhile, the size of such electronics has decreased. The electronics used in advanced diabetes management systems must be protected from biofluids, moisture, and humidity, all while maintaining biocompatibility. For devices that communicate externally, such as those sending signals to monitor, instruct, or track the accuracy of drug delivery, the components required to transmit such information need to be protected without distorting the signal to avoid information delivery failure. Where other coatings may offer one or two of these attributes, Parylene conformal coatings offer all of them and many more.
Understanding the Parylene Difference
Parylene is the name for a group of vapor-deposited, organic poly(para-xylylene) polymers that are often used as moisture and dielectric barriers. What differentiates Parylene from many other types of conformal coatings is that it is applied by vapor deposition — not via spraying, dipping, brushing, or another mechanical form of liquid application (see Figure 1). It is deposited by a gas phase process that does not rely on line-of-sight physics, but literally grows on device surfaces at a molecular level, which means it provides uniform, conformal coverage of all component surfaces, even penetrating the smallest crevices to provide a complete, biocompatible barrier that is only microns in thickness.
Devices to be coated with Parylene are placed in a room-temperature deposition chamber (see Figure 2). A powdered raw material, known as dimer, is placed in the vaporizer at the opposite end of the coating system. The double molecule dimer is heated, sublimating it directly to a vapor. The vapor is then rapidly heated to a very high temperature that cracks (pyrolizes) it into a monomeric vapor. This vapor then travels into an ambient temperature deposition chamber where it spontaneously polymerizes onto all surfaces, forming the ultrathin, uniform, and extremely conformal Parylene film. The entire Parylene coating process is carried out in a closed system under a controlled vacuum. The deposition chamber and items to be coated remain at ambient temperature throughout the entire process and no additional cure process or steps are required.
Parylene is typically applied in thickness ranging from 500 Å to 75 μm, maintaining excellent properties in ultrathin films. A 25-μm coating, for example, will have an electrical insulating capability of 7,000 V. No other coating material can be applied as thin as Parylene and still provide the same level of protection. The molecular “growth” of Parylene coatings ensures not only a uniform conformal coating at the thickness specified by the manufacturer, but because Parylene is formed from a gas, it ensures complete encapsulation of all surfaces without blocking or bridging small openings. All Parylene variants are free of fillers, stabilizers, solvents, catalysts, and plasticizers. As a result, the Parylenes present no leaching, outgassing, or extraction issues. Its naturally low coefficient of friction provides dry-film lubricity properties that benefit moving parts, including syringe and infusion device applications, eliminating the need for silicone oils that are often used as a lubricant in syringe-type devices (see Figure 3).
For implanted devices, Parylene provides components with both biocompatibility and biostability so the device is compatible within the human body and is also not itself compromised by biofluids.
A key feature of Parylene for fluid-delivery devices, and any implantable device or system, is that the ultrathin film delivers necessary protective benefits without compromising the mechanical or functional attributes of the device. As an extremely thin coating, Parylene does not impact the dimension of the device — regardless of how small it is — and ensures biocompatibility within the body. For devices requiring electrical communication, it has other sought after electrical properties such as low dielectric constant and dissipation factors.