By Miguel Solivan, Marketing Manager, Avery Dennison Medical
Medical wearable devices, such as continuous glucose monitors (CGMs), insulin pumps, drug delivery systems, activity trackers and electrocardiogram monitors, are being continuously optimized by their manufacturers for wear time, performance, size and cost. Adhesive materials that are critical for the interface of medical devices with the human body must therefore keep pace with novel device requirements and feedback from users. For example, the promise of extended wear time can not be realized without the availability of adhesive products designed for multi-week wear.
At Avery Dennison Medical, we set out to engineer a medical adhesive system that offers reliable 28-day wear time. We assembled and evaluated mock devices consisting of a polycarbonate disk bonded to a skin-adhesive tape in a skirt-style construction. We then recruited healthy human informed-consent volunteers to wear a randomized selection of prototypes on the back of their upper arms and recorded the times of application and failure (when the prototype eventually detached). We also noted instances of skin irritation and itchiness throughout the 30-day study. Following that, we assessed reliability by analyzing the time to adhesive failure using Kaplan-Meier non-parametric survival analysis. The prototype evaluated in this study exhibited excellent reliability and was well-tolerated with no irritation during wear. The results emphasize the importance of selecting the right adhesive for the application, and that wear performance is dependent on numerous factors including adhesive chemistry, environment, device design, device location and skin properties.
Introduction
Medical wearable devices or “wearables” are typically worn on the human body which allows for continuous, real-time monitoring of physiological functions for diseases such as cardiovascular disease, diabetes and neurological disorders. Wearables have enjoyed remarkable innovation through advances in batteries, electronics, nanomaterials and computing software—and they continue to evolve. Consider how the size and weight of CGMs have decreased over the past decade, improvements made possible by advances in electronics and sensors. CGMs can now boast of longer duration in use, longer battery life and better data management.
During wearable device development, it is essential to balance the mechanophysiology at the interface of the device and skin, with the diverse fragility of skin. The skin is the body’s largest organ and is made of water, proteins, fats and minerals with features of 10-1000 µm height—all of which impact device adhesion and wear time. Keeping devices attached to skin for weeks at a time requires specialized adhesives.
Such adhesives need to allow sensors to perform as expected and monitor activity without interfering or restricting the user’s movement. Additionally, these devices also must be conformable, breathable and comfortable for the user, as quality-of-life requirements are necessary for device adherence.
Materials
This study evaluated wear time for one skin-adhesive tape (MED 5744) and one tie-layer tape (MED 3046) used in combination.
MED 5744 is a single-coated, white polyester (PET) nonwoven with a medical grade acrylic-based adhesive designed for 28-day wear.
MED 3046 is a double-coated, transparent polyurethane (PU) film with a medical grade acrylic-based adhesive on both sides. It is designed to adhere skin carriers to a rigid wearable device.
The skin-adhesive tape MED 5744 and tie-layer tape MED 3046 combination was tested in a wear study trial with a mock polycarbonate device (Figure 1). Each mock device was an island-placed mock device bound to the skin-adhesive tape by using the tie-layer tape. This configuration mirrors the design of commercially available wearable devices, such as CGMs. There were no cover/overlay tapes used in this study.
Summary
Recognizing the complexity of skin, a medical device’s desired performance attributes, and user requirements are critical in selecting the right adhesive system. The proper balance of adhesion, cohesion, tack and breathability is important because a need exists for secure attachment with easy removal. Inappropriate selections could lead to adhesion failure, skin injury and/or device malfunction.
This white paper summaries the results of MED 5744 and MED 3046 in a simulated wear application to characterize the product wear performance. This product combination, in a prototypical wear application, demonstrated excellent reliability and long-lasting adhesion on skin, with an average wear time of 28 days. Subjects found the prototype to be comfortable, with minimal to no itching, no irritation or other discomfort at any point during the study, low pain of removal on Day 30 and minimal adhesive residue left on skin after prototype fall-off or removal on Day 30.
The study showcases the importance of adhesive system selection for medical wearable devices. MED 5744 and MED 3046 have distinct physical properties when tested in a controlled laboratory setting. Skin, on the other hand, is dynamic and varies from person to person. For these reasons, adhesive product testing via wear studies is an indispensable marker for success in medical wearables applications.
It is imperative to determine the right adhesive system early in a wearable medical device’s development process. The adhesive selection is based on the device’s size and shape, its intended wear time, location on the body and the skin’s condition.
While the results from this study demonstrate that MED 5744 and MED 3046 display excellent 28-day wear, the wear time for these products could extend beyond three weeks based on wear conditions, the user environment and product design.
Download the full case study complete with results and charts.
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