Skin is a multilayered organ made of living cells that is constantly changing and growing. The lower layers of the skin are very elastic, meaning anything adhering to it would need to be flexible and have the ability to stretch and move with the skin. The surface of skin is rough (as opposed to substrates like steel or plastic) making it more difficult to obtain proper adhesion. Adding to the challenge, the skin secretes water and oils, and is generally a contaminated surface with dirt, dead cells and bacteria on its surface. When the skin is compromised, it also secretes exudate, which needs to be managed during wound treatment. Also, different adhesives and materials could trigger an immunological (allergic) reaction or sensitivity in the skin, if it is not biocompatible or contains an allergen.
Most adhesives ‘stick’ to the skin by flowing into the nooks and crannies of the rough dermal surface and bonding with the cells on the surface of the skin. Some adhesives absorb fluids which weakens the bond as more and more fluid is absorbed, making it easier for the adhesive to be removed at the end of its wear. Some adhesives, like soft silicone adhesives, adhere to the skin through micro-adhesion, which bonds by only tacking onto certain points of the skin surface which are in contact with the adhesive instead of flowing throughout the surface.
When developing a skin-contact adhesive material it is important to consider not only the delicate nature of skin, but also the application variables and compliance requirements needed to assure the success of the finished medical device:
- Where on the body will the device be worn?
- How long will a device be worn?
- Does the adhesive need to be flexible and conform to the body?
- Does the adhesive need to be water-resistant or repositionable?
Avery Dennison Medical has more than four decades of experience designing adhesives and materials for skin-worn devices. Our adhesive formulations can be customized to support a variety of demanding requirements, from the fragile skin of an infant to the long-term wearability of a glucose monitor to the high conformability and moisture-resistance needed for fitness applications. Our experience means we know which form factors and designs not only work best for each situation, but which are also ideal for scaled production. This insight can save considerable development time for device manufacturers.