Adhesive characteristics
Designing adhesives for extended wear times, and bonding to skin and devices poses challenges for engineers. Engineers developing adhesive wearables can create products that uphold their intended purpose by understanding four characteristics that frame adhesive material performance.
There are three adhesive characteristics. The first is static shear which is the adhesive material’s cohesive strength. Next, we consider the peel adhesion that examines how the bond affects the skin upon removal, tack, and moisture management. Finally, pressure-sensitive adhesives which are designed to quickly and easily bond or have tack and are used in cases where the skin is damaged or fragile. The fourth characteristic is the ability of the adhesive material to manage moisture by absorption or transmission.
These characteristics are fundamental to the duration of wear time, patient activity, and bodily and environmental fluids and moisture.
Types of medical adhesive applications
Wearable devices are designed with the patient’s use in mind and must adhere to different body areas and accommodate various skin types. Avery Dennison develops products that address secure attachment to skin and the surface of the medical device, extended use, and multiple placements on a body.
While they continually develop more diverse solutions, currently, Avery Dennison uses three types of adhesives for wearables to attach medical wearable devices, each providing a solution for specific medical grade adhesive for the skin.
Acrylic adhesives
Acrylic adhesive solutions’ bond strengthens over time while providing a secure bond to the body. As the bond to the skin strengthens on the body , the adhesive flows into the crevices of the top skin layer.
Silicone-based adhesives
Silicone-based adhesives have different applications for wearable devices.
A silicone gel adhesive can be used to apply to the skin for short-term, sensitive skin applications. The silicone gel can be re-applied to the skin multiple times in this format. Silicone-based gel adhesive materials are non-breatheable but can be produced with perforations.
Bonding to a medical device produced from silicone can be challenging. It is difficult to bond to silicone with acrylic adhesives as a low surface energy material. Silicone adhesive has good bond strength with silicone and is often the only adhesive to bond effectively in this design.
Hydrocolloid adhesives
Hydrocolloid adhesives are pressure-sensitive adhesives developed with a rubber base and absorbent particles that help absorb moisture, which will adhere well to the body. Once the hydrocolloid adhesives are saturated with fluids, they thicken, breaking down the adhesive bond and reducing trauma upon removal.
Bonding to skin
Designing wearable devices requires special consideration for patient autonomy, mobility, and discretion. Wearable technology allows patients to remotely monitor and deliver medication in a non-medical setting, like in the comfort of their home.
Wearable advancements accommodate active routines. Lightweight designs and remote monitoring do not hinder mobility. Additionally, the technology allows patients to attach devices to their bodies discreetly, without being noticed. However, this challenges the adhesive material, requiring it to bond to the device and the skin.
Bonding to the device
Medical wearable devices are designed using polymers to be flexible, lightweight, and comfortable. Typically, engineered plastics are used to house the electronics inside the device. A wide range of engineered plastics are used to house devices, ranging from high to low surface energy.
Plastics like polyester and polycarbonate provide high surface energy and are suitable for adhesive bonding. Medium surface energy materials like polyolefin, polyethylene, and polyurethane can be more challenging for bonding. Finally, silicone has a low surface energy, lessening the number of adhesives that will bond with these surfaces. At the same time, high surface energy materials have good bonding but are typically more rigid. Conversely, the lower surface energy materials are more flexible and conformable.
Many factors are taken into account when selecting a device material. High, medium, and low surface energy categories help us understand how to select a suitable adhesive to stick to the device. With this understanding, an adhesive can be chosen or developed, helping to provide the desired attachment and duration required for the bond of the device to the skin attachment material.
Determining a suitable bonding solution by grouping them into three categories, high, medium, and low surface energy, helps us understand how they will stick to the device. With this understanding, a suitable adhesive can be developed and applied, helping to provide the desired attachment and duration required of the bond.
Selecting materials for different layers
Whether it’s to maintain wearer comfort or hold its adhesive bond, each layer that comprises medical wearables serves a specific role. The following tapes are commonly used in material selection for adhesives that hold a device to the patient’s body.
- Short-term skin contact tapes adhere for up to 7 days and are breathable. These adhesive tapes attach the medical device or wearable directly to the patient’s skin.
- Long-term skin contact tapes and short-term contact tapes are alike in their function. The long-term skin contact adhesives can be worn for up to 21 days. However, the skin has a dynamic surface, or substrate that requires the adhesive to manage shedding of the epidermis every 7-14 days, sweat, oil, and hair.
Short and long-term skin contact tapes are designed to hold their bonds through moisture, movement such as exercise, and extended wear.
- Tie-layer tapes are double-coated adhesives bonding the wearable device to the underlying layer attached to the top surface of the skin adhesive. These products provide different adhesives in the construction and have been specifically formulated to bond well to the skin adhesive material.
- Cover overlay tapes are designed to protect and secure the wearable device from external liquids and contaminants, helping the device remain in place.
Design considerations for devices are specific and vary the previously mentioned layers based on the device and “end-use requirements.”
Selecting the right adhesives
Before the wearable device materials are selected, the purpose for the adhesive and fluid handling method must be considered, as the adhesive forms a crucial bond between the device and the user. In skin-worn devices, bonding occurs to the skin with a skin-contact layer adhesive and tie-layer materials bond to the device.
Bodily fluids such as sweating and hair growth can hinder adhesive bonding, ultimately affecting the time on the body. Moisture-vapor transmission and fluid absorption are two methods Avery Dennison uses to manage bodily fluids from affecting the bond.
Moisture-vapour transmission are breathable materials designed with small holes in the adhesive to allow the moisture to transfer through the material to evaporate.
Fluid absorption occurs when bodily fluids come in contact with the adhesive material to form a gel that absorbs and retains the liquids away from the skin.
ADM wearables standard
Avery Dennison’s partners work with experienced suppliers and healthcare professionals to design functional, scaleable, affordable products. Our partnerships with suppliers and medical professionals are based on their ability to uphold optimal material and product standards compliant with regulatory requirements. Keeping pace with new medical advancements means having experienced professionals with more recent approaches from the design stage to the production stage.
Conclusion
Understanding different types of adhesives for wearables is essential to the design, development, and delivery stages with Avery Dennison. Designing medical adhesives for wearables involves consideration of the design purpose of the adhesive, the skin factors in moisture management, textures, comfort, and patient quality of life.
Adhesive characteristics help us frame the design requirements that are fundamental to the functionality, durability, and ability to protect, monitor, and even regulate a patient’s health. Understanding how adhesives stick to the skin and medical devices requires sourcing materials that accommodate healthy to damaged and fragile skin types.
Adhesive materials such as acrylic, silicone-based, and hydrocolloid adhesives are carefully chosen based on their compatibility and ability to bond with specific body areas and the wearable device. In addition, understanding adhesive materials for wearable devices is essential in designing multi-layered medical wearables to perform their singular function as support to the purpose of the multi-layered wearable.
Medical wearable technology is constantly evolving, which means we, along with our partnerships, must continue to develop and adhere to quality standards for the optimal performance of our products.