No medical device designer wants to find themselves responsible for missing or remembering a key consideration too late in the development process – especially when designing a wearable device. Stick-to-skin devices that overlook the human factors could face manufacturing issues, device failures or even cause harm to the wearer, impacting a project’s timeline and budget. Unlike a metal or plastic, skin is a complex organ with many distinct features – from sweating or growing hair to completely regenerating itself every two weeks or so. Each feature has the potential to influence your device’s design. The nature of skin takes careful analysis during design.
 
Use the following questions as a checklist to thoughtfully consider the unique substrate your device will adhere to.
 
1. Has the Device Objective Been Thoroughly Evaluated?
Before starting to design the device, it’s important to take the time to understand who the user is and what they need the device to do every day. That will help you determine the level of intricacy and detail required to develop an effective design.
 
Consider this example: Patients with diabetes rely on their glucose monitors to track the level of sugar in their blood. Their health and independence depend on the device doing its job effectively. Because managing a chronic disease heightens the stakes involved compared to other wearables, such as fitness watches, the level of intricacy and detail that goes into the device’s development is also heightened.
 
While thoroughly vetting the design objective, keep in mind how you can satisfy the user’s needs without overdesigning the device. Overdesigning in hopes of optimizing performance can create more complications than it can solve. For example, overdesigning when it comes to material selection can lead to using too strong of an adhesive for the intended application. If your device only needs to be worn for five days, but an adhesive with a two-week wear time is used, the implications could cause harm to the user. Bring all design decisions back to the device’s objective.
 
2. What Important Wearer Characteristics Are at Play?
Skin is unique to each person, and remembering it is a living, breathing organ that constantly regenerates itself makes it unlike any other substrate. Other important wearer characteristics at play are age, ethnicity, diet, culture and environmental factors. These on top of the skin’s characteristics impact the success of your device design in any given scenario. If the intended wearer is a teenager, expect your device to accommodate skin that produces more oil, whereas if the wearer is a baby or an elderly person, their skin will be more fragile.
 
3. Where on the Body Will this Device Be Worn?
Not only does skin vary from person to person, but it also varies depending on where the device will be worn on the body. There are locations where skin is thicker, hairier and/or oilier, changing the level of sensitivity. Your device design and material selection need to consider where it will be worn and what characteristics this region of the body presents.
 
When it comes to adhesive selection, consider silicone adhesives for thin or fragile skin, such as on a baby’s face. Comparatively, if the device must stay in place for a longer period of time, an acrylic solution may be better to offer stronger adhesive strength. Bringing your materials supplier into this conversation early on can help in finding the best options.
 
4. How Long is the Intended Wear Time of this Device?
To fulfill its purpose, a device needs to stay together and adhered to the skin for its entire intended duration without causing harm to the wearer. Selecting the right materials for the device and its stick-to-skin component helps ensure the skin can breathe and flex as needed while the device is in place. The intended wear time will help you determine the ideal combination.
 
When asking yourself this question, keep in mind that the longer a wearable device is on the body, the more skin’s characteristics come into play. If a device needs to stick to the user for multiple days, generally a smaller, lighter device sticks better than a larger one. When the wearer wants to partake in high intensity activities, an aggressive adhesive might be called for. Vetting what wear time studies your materials supplier has conducted can assist in understanding how adhesives are expected to perform in real-life applications.
 
5. Can Your Materials Withstand Manufacturing?
Manufacturing process and material selection compatibility are important to consider up-front to avoid materials that cannot withstand the stress of your chosen manufacturing process. The consequences of not asking this question early on can include potential redesigns, delays and additional costs.
 
Engaging an adhesive expert who has experience designing, testing and researching adhesive technology can speed up the process. They should also be able to offer support and advice on which adhesives are able to withstand your manufacturing process and also work well with the skin.
 
The best way, and what should be done in every case, to ensure the device is acceptable quality and can withstand under the operation conditions is to test the process before putting it into full-scale production.
 
6. Have You Considered All of the Human Variables at Play?
Before designing your wearable medical device, be sure you’ve considered all of the potential human factors of the application. While your efforts should be exhaustive, don’t let them be exhausting – engage your materials supplier earlier in the process to ease your efforts. Having the right people involved can set your project up for success and minimize risks. Additionally, taking advantage of product selector tools during the design phases, such as 3M’s FindMyAdhesive.com, can also help ensure you select the best materials for your application.
 

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Del R. Lawson, Ph.D., is an R&D manager in 3M’s Medical Solutions Division.
Kris Godbey is an applications engineering & technical support specialist in 3M’s Medical Materials & Technologies.