Advances in Medical-Grade Adhesives

COVER STORY: ADHESIVES

Advances in medical-grade, pressure-sensitive adhesives are being driven by many of the same trends that are affecting healthcare in general. Trends such as an aging population and an emphasis on patient satisfaction have added new challenges to finding the right adhesives.

Medical device manufacturers and, in turn, adhesives suppliers, are responding to the evolving needs of patients and healthcare facilities with adhesive products that dramatically improve functionality and reliability of devices as well as the quality of patient care.

Home Healthcare on the Rise

The trend toward increased home healthcare has put much of the decision making about home-use products in the hands of the patient. In its 2008 Survey of Health Care Consumers, the Deloitte Center for Health Solutions found that 88% of consumers are interested in using home-use devices and online tools that could lead to a reduction in doctor visits and allow individuals to be more active in their own care. The study concluded that many consumers are not only more active in decisions about their care, but that they are also comparing price and quality and are eager to find information and devices that will enable them to perform more of their own care at home.

The growing rate of chronic disease in the United States is also contributing to the proliferation of home-use medical devices. According to the Kaiser Permanente Medical Care Program, two-thirds of Americans over 62 have at least one chronic disease, such as heart disease, diabetes, or respiratory problems. This older population is a heavy user of home monitoring devices, for example.

For makers of medical devices, this means designing more products for use in a patient's home, and many times designing devices that will be used without the direct supervision of a physician or home health aide. This environment introduces a host of challenges when designing devices that require an adhesive component. Challenges include accommodating differing skin types, factoring in the need for long-term adhesion, and ensuring that the adhesive can be exposed to various environments and conditions. It is also critical to consider the weight of the device, which may cause additional strain on the adhesive. A device that consists of multiple layers may be bulky or heavy and thus cause strain on the adhesive-skin bond. Designers should choose an adhesive with increased cohesive strength so that the device can withstand the strain or shear forces to which it is subjected.

Devices designed for home use need to be user-friendly and functional for a broad range of skin types. It is crucial that these devices be appropriate for the application. It is equally important that their use be easy to understand to avoid causing health complications through incorrect use.

Developing adhesives that adhere to the skin has proven to be a tremendous challenge. In fact, skin-related applications have shaped the way medical-grade adhesives are designed. It is important to consider the various factors that determine skin type, such as age and ethnicity. In addition, some devices may be used by anyone from middle-aged to senior citizen, such as a diabetic device or a wound-care application. Adhesives for such devices need to be functionally diverse. Significant advances are being made with the development of adhesive product lines that are as diverse as the patients being treated. These adhesives consider factors such as ethnicity, gender, age, where the device will be used, and patient lifestyle.

Home-use devices need to be simple, nonpainful, and nonirritating. An ostomy device, for example, presents a unique set of challenges. For this device, the adhesive needs to stand up to daily dressing changes—often by the patient. It is a device that is used on a broad range of skin types, and yet it must be strong enough to hold up to the weight variations of the device brought on by the discharge from the ostomy into the collection bag. The device's adhesive must be strong enough to withstand the physical activity of the patient, while maintaining a good seal or bond to the skin. The device must adhere to the skin, but it can't be so aggressive that it's painful or damaging to remove from the skin. As with any device for which daily dressing changes are the norm, the more it has to be changed, the more susceptible it is to disrupting the healing process. It is essential that the adhesive causes no skin irritation or other complications.

More than ever, patients expect options when it comes to healthcare, especially for home-use medical devices. The measurement of a patient's overall satisfaction goes beyond the actual treatment of the ailment. It is also gauged by level of comfort. Even in hospital settings, if a product is difficult to use, in­effective, painful, or irritating to the skin, brand reputations and performance ratings can be negatively affected. Adhesives suppliers continue to work toward the ideal adhesive. The ideal adhesive will adhere well, even with movement, and will only come off when it is removed by the patient or caregiver.

Multifunction Adhesives

A newer, more-comprehensive cardiac stress test illustrates the need for multifunction adhesives that allow for long-term adhesion. Instead of a 30–40-minute stress test in which the patient is monitored with electrodes for a relatively short period, devices are being developed that would be worn by the patient for several days. This extended test allows the physician to continually monitor heart rate changes and irregularities over a longer period and in the patient's own typical environments. This longer test provides more and better information for the physician.

In this application, the device is exposed not only to physical movement but also to the patient's perspiration, showering, and changes in body heat. Such factors therefore require a high-performance, long-term adhesive. Adhesives with extended-wear capabilities are being developed to meet this demand. And as adhesives suppliers consider length-of-wear characteristics in their designs, maintaining comfort and minimizing moisture levels are a critical part of the challenge. Minimizing moisture levels helps to prevent maceration of the skin. This can be achieved through the use of adhesives that offer breathability or increased moisture vapor transmission rate (MVTR) levels. MVTR is the rate at which water vapor permeates through a film.

Physical environments and additional functional requirements are other considerations for device designers and adhesives suppliers. Where on the body will the particular device be worn? How does placement affect the requirements for the adhesive?

An ostomy bag, for which weight is a consideration, can also illustrate this challenge. For this device, the adhesive has more physical demands. Another example might be a device worn on the bottom of the foot. In this case, mobility and variations in weight and stress on the device must be considered when choosing an adhesive. Restricting such patients to their beds could lead to the development of ulcers or other complications from lack of mobility. Therefore, the device needs to be designed with comfort and durability in mind.

Devices that are worn at home are also becoming more complex. Many consist of multiple layers to accommodate flat battery technology, radio-frequency identification tags, and antennas, to name a few. Adhesives suppliers have responded to this trend by developing high-tack, high-shear applications that also address concerns such as skin types and biocompatibility. Today's adhesives are much more functional in terms of maintaining adhesion after exposure to fluids, during physical activity, and for longer periods of time. It is imperative that medical device designers consider the variety of technologies available and select one that is appropriate for the device being designed.

Advances on the Surgical Side

As with home healthcare devices, surgical devices also need adhesives that address many of the same issues, including different skin types, long-term adhesion, and various environments and conditions. For surgical devices, treatment diversity and complexity combined with the increased risk of complications and infections present an exponentially greater challenge. For instance, in this application, surgical drapes and incise drapes must maintain excellent adhesion to the skin during surgical procedures to prevent bacteria from entering the surgical site or incision.

The environment and patients' comfort are the primary concerns in the development of adhesives for surgical applications. These adhesives are designed to improve patient comfort by being nonirritating to the skin and to prevent infection by achieving an impenetrable seal that keeps out bacteria. Without a clean adhesive-to-skin seal, for example, infections can result—and, in turn, can lead to longer hospital stays, drive up hospital operating costs, and delay or complicate a patient's recovery process.

According to the Centers for Disease Control, an estimated 500,000 surgical site infections (SSI) occur each year in the United States. Medical device designers who understand the advances in today's adhesives can design devices that help to decrease this number. Working with the most appropriate adhesive allows for a safe, firm adhesion in drape-to-drape and drape-to-patient applications, which helps lower the overall risk of SSI. Surgical drape-to-drape construction adhesives pose a particular challenge because they must be able to adhere to a wide range of materials that may have coatings for repelling or absorbing blood or other body fluids.

Breathability, or the rate at which water vapor permeates film, is another key factor for devices in surgical applications. A product's breathability can play an important role in the healing process. The highest level of breathability is not always the best case, however. Depending on the application, wound-care dressings, for instance, always need a certain level of moisture, to allow for optimum healing.

A surgical incise drape is a good illustration of the need for breathability. An incise drape is usually made of thin-gauge polyurethane or film because of its inherent breathability characteristics. After being applied to a patient's skin during a surgical procedure, the surgeon makes the incision directly through the film. Its purpose is to protect the patient from bacterial infection. To design the right system, the combination of film and adhesive must be optimized in order to provide the desired MVTR. Advances in adhesives systems today enable designers to tailor an adhesive to change the level of the end product's breathability. Specifically, to create the required MVTR, an adhesive would be formulated such that, when applied to the film, it would achieve the desired MVTR level. MVTR can be altered through the choice of film, adhesive, or both.

Conclusion

It is imperative that product quality begin in the earliest stages of design and development. Today's adhesives are asked to play a larger role in helping designers meet this challenge. There is a greater availability of adhesives that are tested according to ISO 10993 standards on cytotoxicity, skin irritation, and skin sensitization in a broad range of surgical applications. Many new adhesives are suitable for a more diverse range of materials, such as low-
surface-energy films or plastics, surgical drapes, foams, wovens, and nonwovens. Biocompatibility is dramatically improved, and these adhesives better withstand autoclave, gamma, and ethylene oxide sterilization.

Perhaps the most significant advance is the greater ability for customization. As demand for medical devices that are more patient friendly continues to expand, adhesives become part of improving the experience. Many adhesives suppliers are not limited to stock products. Rather, they can partner with the device designer to develop a custom application to jointly develop adhesives that improve safety, comfort, and ease of use.

Aaron Smith is technical marketing manager at MACtac Medical Products (Stow, OH). He can be reached at [email protected].

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