Sticking With It | Selecting the Right Adhesive for Your P-S Medical Application

Development of new pressure-sensitive products for medical use is one of the more challenging areas for the product developer.

The use of pressure-sensitive adhesives (PSAs) in medical applications is another example of end use breadth as well as a testimony to innovation. From the simple bandage strip to the transdermal patch, most of us will have encountered pressure-sensitive based medical products in our daily lives. We then should consider how tapes also are used in a wide variety of pharmaceutical labeling and diagnostic assembly applications. It all adds up to the fact that pressure-sensitive based products play a vital and growing role in the medical field.

As with the other market areas we have explored in previous articles, careful consideration of the adhesive component of a medical product is vital. While regulatory considerations are important in the other markets, for medical applications they are much more of a factor, and perhaps, one of the first criteria to consider when looking to develop a new product. In general, medical products will require added focus on manufacturing and testing resulting in longer development time when approvals are required.

These are all things to keep in mind as one considers entering the medical arena—will the size of the prize be worth the time and effort? With an aging population, more in-home and facility-based care, use of bandage and transdermal products is projected to keep growing, so it is an attractive market. As I have indicated in prior articles, it is imperative to do the upfront market research and determine if this attractive market is indeed one where the requirements to participate fit your company’s capabilities or are worth the investment.

So, let’s talk a bit about the range of applications where PSAs are used in the medical field. Let’s begin with the non-skin contact uses. This may be a great place to start if you have not previously participated in medical applications as it is less regulatory-intensive than skin contact uses. As previously described, pressure-sensitive labels are used for the span of products from syringes to the vials of medication obtained at the local pharmacy. Transfer tapes and double-sided tapes are used in diagnostic and laboratory equipment assembly. The checklist previously included for these market areas also would apply to these medical applications but now brings some added complexity.

MEDICAL LABELING

First, let’s briefly talk about labels. One key criteria for medical labeling is that the adhesive needs to be permanent so that the facestock is destroyed before the bond. This assists the pharmacist or clinician in ensuring product identification and integrity. Mandrel hold—the ability to hold the label in place on a highly-curved surface—is a key criterion for syringe and vial labeling. Temperature stability for specimen labeling can include maintaining bonds to very low temperatures, sometimes as low as 40 deg below zero!

For diagnostic applications like instrument assembly, pressure-sensitive tapes offer the benefit of a strong continuous bond allowing for no fluid leakage. In general, the adhesives used must withstand sterilization, be fluid resistant, non-migratory, and low outgassing.

Since the adhesive bond may encounter the bodily fluids being tested, these last two criteria are especially important. The adhesive cannot interfere in the testing of the fluids, and minor components that either migrate or leach from the adhesive could cause false test results. This requires careful upfront evaluation, and therefore, increases the development time prior to offering a new final product.

skin contact

So next, let’s move to skin contact applications for PSA products. These include, but are not limited to, bandage strips, medical tapes, and surgical drapes. So, what is important here? First and foremost, the adhesive must have good adhesion to the skin. The strength of the bond will depend on the time the product will be used, which varies by use. For instance, children will typically only wear a bandage strip for a very short period of time (especially if the pack offers different favorite characters!), while in transdermal drug delivery, a patch can be in place for a week or longer.

The product also needs to be comfortable to wear so the adhesive must be able to “stretch” with the skin, at least to a small degree. Some moisture tolerance, so the bond is maintained, as well as painless and clean removability are also important features. And, of course, products must be non-irritating, non-sensitizing, and non-cytotoxic.

So where to begin? Here is where working with a reputable and established adhesive supplier has many benefits. They will have already completed detailed safety assessments of their products to ensure they are suitable for use on the skin. The most common certification is meeting the requirements of ISO 10993-5 and 10993-10. These certify that the adhesive is non-cytotoxic, non-irritating, and non-sensitizing. Biocompatibility testing must be done on the final construction. Adhesive suppliers will provide a formal Safety Assessment letter for product they promote for medical applications.

A key factor in determining what type of adhesive to use will be the length of wear for the final product. Short duration wear leaves many options, including a variety of hot melts, water-based acrylics, as well as solvent-based acrylics and silicones. For short-term use applications like bandage strips, hot melts and water-based acrylics are frequently the product of choice due to ease of preparation and cost. Anyone who has worn a bandage strip for a longer period will have seen the whitening of the skin when it is removed. This is because no moisture is transmitted to the skin when covered.

If the bandage will be in place for a longer period, say to cover an incision, then a “breathable” product is recommended. Here both the facestock and adhesive must allow moisture and air to be transmitted to the wound. This allows for healing while still providing protection. Facestocks are available that are specifically designed to be breathable. Adhesive suppliers also have developed products that allow for moisture transmission. Both components must be considered “breathable,” i.e., if the adhesive allows moisture to wick from the wound surface and it cannot be transported across the facestock, the bandage may fail at the adhesive-facestock interface. There are many solvent-based acrylics and silicones that are known to be “breathable.”

Data developed to determine moisture-vapor transmission rate (MVTR) provides a standard method of comparing the efficacy of various adhesives. Testing is done using ASTM and USP standard methods in which sample laminates are evaluated under precise temperature and humidity conditions in the laboratory. Results are reported in g/m2/day.

TRANSDERMAL PATCHES

Transdermal drug delivery patches are a highly specialized pressure-sensitive medical application. The difference is that a transdermal product will include drug actives. The drug is mixed into the adhesive matrix before it is coated to the liner or facestock during manufacture. When the batch is applied to the skin, the drug slowly migrates through the adhesive, is absorbed through the skin and into the body to provide the medication. In addition to all the considerations of adhesion, removal, cytotoxity, etc., now there is the added dimension of drug solubility and release to consider.

The final product construction also will need FDA approval, so this is not an area to enter without very careful deliberation. Development time for a new transdermal drug delivery product will take several years of development, testing, and waiting for approvals. Close collaboration with the adhesive supplier is vital.

Adhesives used for patch development must have an FDA Drug Master File (DMF), which the developer can access and reference in their filing. Similar registrations also would be available for outside the U.S. to support filings. The adhesives also should be manufactured in an ISO 9001 facility following IPEC-GMP (International Pharmaceutical Excipients Council – Good Manufacturing Process) guidelines. Adhesives are considered excipients, that is, a constituent of the medical product (the patch) that is not the active ingredient or packaging.

Development of new pressure-sensitive products for medical applications is probably one of the more challenging areas for the product developer. In addition to considering the performance factors normally associated with creating something new comes the oversight of regulatory and safety concerns. All require a longer development cycle time, which means being patient to realize the benefits of the new product. Not an area to consider entering lightly; doing a very comprehensive market assessment prior to development will help to manage expectations. Close collaboration with the adhesive supplier will ensure that the adhesives considered meet regulatory requirements and are deemed safe for use.

Hopefully this article will provide a good insight into the medical area of pressure-sensitives. Questions? Just send me a note, and I'll be happy to try to provide added information.

Until next time, keep Sticking With It...

About the Author

Ingrid Brase is a technical market strategist recognized for her ability to translate technical needs into business solutions. Her understanding of pressure-sensitive adhesives and their use is complemented by her strengths in strategic marketing, project management, new product development, and key account management. She is available for consulting or contact assignments in these areas. Ingrid’s expertise is a result of more than 20 years of experience in the p-s adhesives business. She was most recently the market segment director for Henkel Corp., rising to that position after various assignments in the p-s business unit. She began her career as a research scientist then progressed to market-focused roles. Ingrid earned her MBA at Rider Univ. and holds a BS in chemistry from SUNY/Oneonta. She has served on the board of directors for TLMI and AIMCAL in addition to chairing technical teams for both trade associations. Ingrid is a well-known speaker and author on topics related to adhesive use. To learn more about Ingrid or contact her, visit www.ingridbrase.com, e-mail to This email address is being protected from spambots. You need JavaScript enabled to view it., or call her at 609-558-9760.

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