Skin basics
Before we dive into how we design our products for performance and comfort, let’s examine the multilayered characteristics of the skin from health factors, varying textures, contours, moisture management, and environmental effects on the skin.
The surface of the skin and the lower layers perform different functions and, therefore, have different textures and contours. The lower layers of the skin vary in elasticity, requiring the adhesive to be flexible and expand with the skin. Adhesion to the skin’s surface is more challenging due to its rough texture. The surface skin releases oils and water, dirt, dead cells, and bacteria, contaminating the skin and making bonding to the skin more challenging.
While the general structure of the skin is the same, everyone’s skin is different. As a result, end users have different experiences when placing skin-worn wearable devices on the body. Allergic reactions can occur to sensitive skin if the adhesive materials aren’t biocompatible or if the adhesive materials consist of allergens.
It is essential to determine the following during the design and development stages to protect the skin during end use:
- Where on the body will the device be worn?
- How long will a device be worn?
- How heavy is the device being worn?
- Does the adhesive need to be flexible and conform to the body?
- Does the adhesive need to be water-resistant or repositionable?
Application variables, compliance requirements, and the skin’s sensitivity must be considered in developing the medical device and the adhesives joining the device to the skin.
Body placement considerations
Body placement for wearable devices is a significant design requirement because designers must consider wear time, monitoring and data accuracy, and performance (adherence and peel adhesion, moisture management, and static shear) to determine a device’s placement on the body. These factors must always be considered as the user experience ultimately is about their comfort, compliance, and functionality.
In non-medical settings, a patient’s autonomy depends on the medical wearable device to maintain its bond to the skin and the device for its intended duration. The body placement ensures the device will adhere through the patient’s daily activities and must account for the release of bodily fluids.
Wearable devices that monitor and collect data from the patient must be designed to access the device easily- so the user can accurately transfer the data into a cloud computing infrastructure in a non-medical setting. Often, that transfer of information is managed wirelessly by Bluetooth or by removing the device from the skin adhesive to download data.
How important are adhesives to designing wearable solutions?
Adhesives are pivotal in medical wearable device design as they are the foundation for building a medical device. Designers consider two classifications when designing devices: adhesive purpose and adhesive fluid handling method. These classifications determine how the adhesive adheres to the skin and device and how and where the device is worn on the body.
Materials designed for skin-worn devices that bond directly to the skin are called the skin-contact layer. The materials that connect the device to the skin-contact layer are called the tie-layer materials. Both help to determine the adhesive purpose in the early stages of the design process.
Wear times are crucial to determine which material’s performance characteristics work best in designing extended wearables that manage sweat, oils, and excrement from the skin. The adhesive fluid handling method allows designers to search for suitable materials to contain bodily fluids, ultimately determining the wear time functionality and the patient’s comfort.
Materials for adhesive fluid handling manage fluids in two ways. The first way, Moisture-vapor transmission, is achieved as moisture moves through the adhesive and the carrier material that channels moisture through the adhesive, evaporating at its surface and classifying it as breathable. Many different material combinations have varying degrees of breathability, which is one factor in the design.
Fluid absorption is the second approach. Some adhesives, like a hydrocolloid adhesive, are specifically designed to form a gel that helps absorb fluids away from the skin, preventing skin irritation and damage. Other adhesives allow moisture to flow through to the carrier material, which can absorb some moisture. Typically, a polyester non-woven or a polyurethane non-woven exhibit that trait.
Adhesives are essential in designing skin-worn medical wearables; therefore, the adhesives used to stick to the device and the skin must be compatible. Skin contact adhesives, tie-layer adhesives, and cover/overlay tapes (protect the device from dirt and water) must work together by being breathable or absorbing moisture away from the skin. Adhering comfortably to the skin without irritating it is undoubtedly the cornerstone in selecting a suitable adhesive.
Conclusion
Skin characteristics and body placement are essential in designing medical adhesives but are critical to the end user’s performance and comfort during wear time. Determining the correct adhesives for the skin and the device involves testing the adhesive materials to source compatibility with the device and the skin.
In instances where tie layers are required, the adhesive materials used for the skin contact layer adhere comfortably to the skin in a functional placement for the user’s autonomy, mobility, and discretion without causing irritations or damage during wear times.
Tie-layer tapes hold the device together, and the cover/overlay tape protects the device from environmental contaminants such as dirt, adding another layer of securement to hold the device in place.
The adhesive layers must also account for moisture vapor transmission or fluid absorption, protecting the skin from bodily fluids, skin functions, or wound excrements.
Material performance is the connection between keeping the device fixed on the body, user comfort, and functionality.
