Developers of adhesives used to affix wearable medical devices to the skin must overcome a host of physical, demographic, and design challenges.
Although most wearables used in the healthcare space today are not classified as medical devices, the market for medical device wearable technologies is expected to grow to more than $5 billion by 2018. But in order to work, medical device wearables still have to be affixed to the body, necessitating the design and development of new adhesives. However, developing adhesives for wearable applications is no easy feat. Designers can create effective products only by knowing the skin type and age of the target patient population and by understanding the physical properties of the wearable device itself.
The Devil’s in the Details
“In designing a wearable system, most companies use adhesives that are already familiar to the regulatory bodies,” comments Martha Sloboda, director, global business development at Windsor, CT–based Scapa Healthcare. “Thus, they begin with such standard materials as acrylics, silicone, or polyurethane adhesive chemistries. But then it comes down to determining whether the device will be used under the clothing or whether it will be fully exposed, whether it will be exposed to moisture, whether it is a long- or a short-wear application, whether it will be affixed to a joint or a flexible site, whether it will be attached to broken or unbroken skin.”
Adhesives are all about fixation, but fixation means adhesion to the skin as well as to the device, explains John Bobo, Scapa Healthcare’s associate director, R&D for healthcare, North America. “The construction of a suitable adhesive for wearable medical device applications isn’t always straightforward. You must make sure that all the components work together, including the skin adhesive, the substrate, and the device-hold adhesive. This means that an adhesive for these applications will have two different types of bondable surfaces.”
Some types of adhesives might be better at holding a device and some might be better at adhering to the skin, Bobo adds. Designers must consider this factor when they develop the whole adhesive system. “We create adhesive products by building variations and experimentation. Sometimes, we find that if we put the same adhesive on all layers, it doesn’t work as well as if we use different adhesives on different layers because of the interplay of the different substrates and the skin.”
Scapa produces its adhesive chemistries and constructions by building layer upon layer to achieve the necessary structural integrity required by the total product, Sloboda notes. Thus, a system might have an adhesive chemistry on one side, a binding layer, a different adhesive chemistry on the other side, and a removable liner.
However, depending on the geometry of the device and the body surface and how the liners will be removed, the design can be as important as the adhesive itself, Sloboda adds. “Thus, you have to look at the choice of adhesive holistically.” Ultimately, the final question that the design team must weigh is achieving performance benefits versus avoiding critical failures. “If a critical failure means that the product will fall off, it may be necessary to select a more tenacious adhesive, one that may cause the patient discomfort when the adhesive is removed. The tradeoff is that the product won’t fail.”