Pressure-sensitive adhesives (PSAs) have long been recognized as a cost-effective assembly method, due to their ease of use and ability to hold two surfaces together solely by surface contact. Demonstrating firm adhesion to many surfaces and a wide range of tack and peel properties, PSAs are ideal for use in industries with specialized bonding needs, such as medical device manufacturing.

Medical devices must be specially engineered for safety and effectiveness, and they must comply with strict guidelines related to sterility and human contact. Does the material comply with Food and Drug Administration regulations and good manufacturing practice guidelines?

For instance, many external medical devices adhere directly to skin. Thus, PSAs for these applications should be tested to ISO 10993-5/-10 standards for cytotoxicity, skin irritation and skin sensitization to ensure biocompatibility.

With all of the safety concerns implicit to medical devices, manufacturers often turn to flexible PSAs as a reliable, easy-to-handle means of creating firm adhesion without harming the patient’s skin.

Meeting Medical Needs

PSAs are especially useful for addressing three core needs in medical device manufacturing:

Adhesion. PSAs deliver instant adhesion with no additional curing time. Their level of adhesion can be tailored to match many application needs, and they remove cleanly after use. Because they don’t have to be metered or mixed prior to use, their properties remain consistent from day to day or batch to batch. The ability to manually apply the adhesive with little pressure and still create a firm bond is essential in the medical device industry.

Breathability. PSAs are frequently designed to enable moisture from the skin to dissipate, allowing for a more lasting hold. Depending on the adhesive and face stock, breathability properties can be customized so the device can be worn for short or long periods of time. The adhesive’s moisture vapor transmission rate is a key measure of breathability.

Functionality. To ensure flexibility, PSAs are engineered to match multiple substrates, whether film, foam or nonwoven. The goal is for the adhesive to conform with natural body movement while meeting adhesion requirements.

To grasp why adhesion, breathability and functionality are so crucial to medical device manufacturers, it is necessary to understand the common applications for medical-grade PSAs. These adhesives are most often used to assemble disposable, short-term-use devices. Typical applications include bandages, disposable electrodes, electrocardiogram pads, monitoring electrodes, intravenous line securement, island dressings, automated external defibrillator pads, grounding pads, ostomy applications, incised surgical drapes and device assembly.

Medical-grade PSAs can also be used to make transdermal drug delivery devices. These systems consist of a drug-infused patch that is bonded to the skin with a specially formulated PSA. These devices deliver medication into the bloodstream more quickly than oral drug administration.

Regardless of the application, it’s important to choose a PSA with the correct adhesion and environmental resistance properties. Knowing what to convey to an adhesive supplier regarding surface constraints and environmental exposure is critical in selecting the best PSA for a medical device application.

Surface and Environmental Considerations

When choosing a PSA, it’s important to consider the properties of the surface to which it will adhere. Since many medical devices attach to the skin, biocompatibility is important. Skin is not a predictable surface. It can vary significantly from person to person based on race, age, gender, area of application, patient lifestyle and numerous other conditions.

Other surfaces to which a medical PSA may be required to bond, include drape fabrics, spunlace, Kraton, spun-melt-spun fabrics, polyethylene, ethylene-vinyl acetate, tubing, stainless steel, foam and films.

Environmental exposure is also essential to consider when selecting a PSA for a medical device. Will the device be subjected to moisture, heat or cold? If the device will adhere to the skin, it’s important to use an adhesive designed around a person’s daily life. Showers, sweat and friction from body motion are all factors that must be accounted for during design. Anticipated exposure to certain chemicals, such as alcohol, Betadine and antiseptics, also can have an impact on the best formulation for a PSA.

Many medical devices must be sterilized for use near open wounds. Surgical site infections complicate an average of 5 percent of surgeries in the United States every year. As a result, medical-grade PSAs are designed to remain stable after exposure to sterilization processes, such as ethylene oxide (ETO) gas and gamma rays.

Given the myriad surfaces, chemicals and environmental conditions to which medical devices might be exposed, it’s important to test PSAs in the application before settling on a particular formulation. For example, if the PSA is expected to carry weight, engineers should conduct shear- and tensile-strength tests. The longevity of the device is also an important consideration. Does the bond have to last days or weeks? PSAs can be tested for short- or long-term wear.

Types of PSAs

While the process for creating medical-grade PSAs is similar to that for conventional PSAs, the adhesives must be compounded differently to bond with skin without causing irritation or damage upon application or removal. These adhesives must be strong enough to hold onto a medical device, but cannot leave any residue or cause discomfort upon removal. To accommodate these divergent performance needs, a variety of PSA constructions and formulations are available.

Acrylic-based PSAs exhibit instant adhesion. They are biocompatible and can withstand ETO and gamma ray sterilization. When coupled with polyurethane carriers, acrylic PSAs are especially useful for long-term wear applications with substantial breathability requirements.

Like acrylics, rubber-based PSAs deliver instant adhesion and can withstand ETO and gamma sterilization. They adhere well to low-energy surfaces, but can be removed gently from skin without causing irritation or leaving behind residue. Made from latex-free material, these PSAs can be applied to devices via hot-melt, solvent or emulsion methods, or as a single- or double-coated product.

With the many highly engineered, customizable PSAs available to medical device manufacturers, finding a supplier with technical expertise in medical-grade formulations is advisable. Open communication with an adhesive supplier regarding regulatory compliance, environmental resistance and other unique production and performance requirements will ensure peace of mind.

With research being applied to PSAs in the fields of dissolvability, miniaturization and wide-web ultraviolet coatings, staying connected with the right PSA supplier can make all the difference in maintaining a competitive advantage.