3M's guide for designing wearable medical devices

Del R. Lawson, research and development manager and Kris Godbey, applications engineering and technical support specialist - both from 3M, discuss how to design wearable medical devices.

Wearable medical devices are notoriously challenging design projects. One way to increase your chances for success is by considering the unique substrate to which it will stick – the skin.

Unlike a metal or plastic, skin sweats, grows hair and completely regenerates itself every two weeks or so. It also changes with health, diet, activity level, environment and age. Often patients may have underlying medical conditions, such as diabetes, and thus their skin requires special attention. Stick-to-skin devices that don’t take these factors into account could result in manufacturing issues, device failures or even harm to the wearer, which can impact a project’s timeline and budget. The good news is that most mishaps are largely preventable.

Here are five variables you must accommodate in order to stay on track when developing your next stick-to-skin wearable product.

1. Device objective

Prior to kicking off the design process, it’s important to build a thorough understanding of the device - who it will be used on and what its end goal will be. Think about what the wearer relies on the device to do for them every day. For example, patients with diabetes rely on their glucose monitors to track how much sugar is in their blood. This type of device requires intricate design and high attention to detail because the wearer’s health and independence depends on whether the device does its job effectively. When it comes to managing a chronic disease, stakes are higher than they are with other wearables, such as fitness watches. While it’s still important for those, or other activity trackers, to provide accurate readings, there is less on the line at the end of the day.

It’s also not uncommon for the “less is more” saying to be true for stick-to-skin devices. Overdesigning a device with the intention of optimizing performance can backfire and create more complications than it will solve.

As it applies to material selection, overdesigning might mean selecting too strong of an adhesive for the intended application. Selecting an adhesive with a two-week wear time for a device that only needs to be worn for five days could result in harm to the user, so it’s important to keep it simple.

2. Wearer characteristics

As mentioned previously, skin is a living, breathing organ that’s constantly regenerating itself, making it unlike other substrates. Those characteristics coupled with variables including age, ethnicity, diet, culture and environmental factors all play into how successful the device will be in a given scenario. For instance, if the wearer is a baby or elderly, their skin will be more fragile than a healthy young adult. Teenage skin, on the other hand, usually produces more oil, creating its own set of stick-to-skin challenges.

3. Location

Where the device will be worn on the body matters. In some areas, our skin is thicker, hairier and/or oilier, influencing how sensitive the skin will be in that location. Device design and adhesive selection, particularly if they’ll come into contact with skin, need to take into account where it will be worn and the characteristics unique to that region of the body. For applications that require wear on thin or fragile skin, like on the face or on the elderly or babies, silicone adhesives might be best. If the device needs to stay in place for longer periods of time on an area that can withstand stronger adhesive strength, an acrylic solution may be the better option. It’s a good idea to discuss the best options with your materials supplier.

4. Wear time

In order for the device to fulfill its purpose, it has to stay together and adhere to skin for its entire intended duration without causing harm. That means selecting the right combination of adhesive and backing to attach the device, as well as the material housing the device. Careful selection of both will help to ensure the skin is able to breathe and flex as needed while the device is in place. Generally, a smaller, lighter device is better for sticking over multiple days than a larger one. Devices that are attached to the skin during high intensity activities, such as running or biking, may call for an aggressive adhesive. Keep in mind that humans are living, moving, breathing, flexing beings, and therefore what we put on our bodies should accommodate this. Checking with your materials supplier about any wear time studies they’ve conducted will help to increase your understanding on how adhesives are expected to perform in real-life applications.

5. Manufacturing processes

Materials that might work well in your device’s design may not withstand the stress of manufacturing. Consider how the device will be manufactured early in the design process to avoid potential redesigns, delays and additional costs. If your device or its materials require sterilization, test them with your desired methods to help determine whether or not it will be compatible with your project and application. Additionally, engaging adhesive experts who have experience designing, testing, researching and innovating adhesive technology can speed along the process. They will be able to offer support and tips on which adhesives are able to withstand manufacturing, as well as those that work well with skin. In every case, before using any product in full-scale production, device manufacturers should conduct their own tests to determine whether the product is of acceptable quality and is suitable for their particular purposes under their own operating conditions.

Before your stick-to-skin product will be ready to bring to the masses, it’s important to consider the human variables at play. Engage your materials supplier early on in the process. Collaborating with materials experts at the start will set your project up for success and help you avoid future risks later in the process. Additionally, utilizing product selector tools during the design phases will help ensure you are using the best materials for your application.