I know a lot of people dislike being advertised to, but I lap it up, depending on what it is. This morning, LinkedIn had a suggested post, on skin adhesives for wearable devices by a very knowledgeable 3M Professional. It makes for a very interesting read, and I recommend you peruse it, from the linked reference below. Just so you know, I do NOT have any relationship, financial or otherwise with the organization, in case you are wondering.
The article had a lot of good advice, basics yes, but worth the refresh. I thought I would recount some, with a few thoughts of my own.
It is true that adhesives must be understood and tested before and during design. It is also important not to over-design, and to pick and use an adhesive that is just appropriate for the application.
Now, I want to recount a few thoughts, also relevant to skin, wearables etc., from my own design and use experience:
1. Understanding Skin
My first major project in graduate school was as part of a team, where we designed a skin testing device for Unilever. They wanted us to design a device that would reproduce a measure of one of skin's properties. We searched and searched, and learned a lot about skin through the design process. We even met a quirky expert in skin research at UCSF and learned a lot from him. This is the first step in design. Education. Skin is very quirky. It is an organ, the largest in the human body, and essentially, its outer layers are dead. It destructs and regenerates on a fairly regular basis.
Skin varies in its properties based on the sex, age and race of a person, sure, but it doesn't stop there. It ALSO varies based on the exposure of the person to sun and other environments harsh or gentle. Exposure to moisture, illness and other factors also change its properties and nature.
Skin doesn't just protect your internal organs, which it does really well by the way, it also engages in thermoregulation through sweat.
All in all, it is a very fascinating organ. And you need to understand it deeply and well. Hire a skin expert. Talk to a number of them, but more importantly, you HAVE skin (in the game, and otherwise)! Well, duh! Your designs - you should try them on yourself. I will expand on this later, but unless we are talking about ablation and such, for most other products, such as wearables, you have no excuse if you are not using the devices on yourself, at least at some basic level to develop a much better understanding of skin and its properties.
2, Testing Skin
So, in our design project, after much learning and planning, we wanted to measure torsional stiffness as an analogue to skin elasticity. We theorized that skin that is exposed to harsh environments, or skin in older people would be less elastic and thus stiffer. We designed our device and with the generous help of a Design Expert from IDEO turned our prototypes into a beautifully 3D Printed device in 2002!
However, well before we got there, not only were we testing ourselves, we were also testing others. Our device needed to attach itself to skin temporarily. We, in fact, found these wonderful, round, adhesive-backed, single use Velcro Pads (that I remembered today, after all that time) that 3M made, for attachment with skin. We liked it, and it ended up dictating the size of our shaft, but would other people?
So, in a way, that if we were a real company would have gotten us in a lot of trouble, we went down and waited outside Stanford's famous TreeHouse eatery and just asked people to tell us what they felt like, using our device. We had done this with the famous "dark horse prototype" as part of our class, where we had literally used Digital Calipers (Vernier's Calipers for those with a British/Indian background) to stretch skin and see how it bounced back. That time, we had used double sided sticky tape (yuck, yes, but prototype, remember!)
In return, we told them what we were doing, and gave away chocolates (perhaps for a future dental device project, maybe? :D ). I do not suggest you do that. But, like we did in a start-up I worked for, later, you can get an IRB and do some testing on people, compensating them for real cash. Ask them about how they feel wearing, or using or testing with your device. Ask them about comfort and seek to understand.
Even before that, make sure you like it. If you can't dogfood your own devices (perhaps, not the right attitude when designing a radiotherapy device), why use it on others. For example, we quickly ruled that men like me, with large, grubby, hairy hands are NOT the ideal candidate for our device! Velcro can stick to hear and make you uncomfortable!! Unilever mainly wanted to market this to women, so this was not a huge drawback you see....
3. More On Testing
I interned at a start up focused on a wearable blood glucose diagnostic device that was trying to use 100nl - 250nl of blood only for glucose level testing. The idea was to encourage diabetics to actually test themselves up to 4X a day, a plan for which the adherence was quite low. The reason is simple. It is QUITE painful to test yourself when a device requires higher quantities of blood. Do you know how I know? We tested ourselves. Me, other engineers, and even non-engineering employees in the start up. Lancing causes quite a bit of pain, and then if you lance yourself enough times, your vessels get protected by, you guessed it, your skin, and they go deeper and getting blood out is even harder.
We even joked about carrying some paperwork to show we weren't addicts, in case we were pulled over. We half-joked actually. We really had that many lances on our arms, forehands, etc. Because, even with recruited patients, we could only get so many draws out. For the rest, and to gain a deeper understanding, we did have to lance ourselves quite a number of times.
Yes, there is a CLEAR market for non-invasive blood glucose testing!
4. Wear Your Wearables
Or, at least wear someone else's. I bought this Fitbit Surge, almost 16 years after the last watch I wore! I did, in the interim try to get back to watches, but I just gave up as the phones were able to tell time. Of course, the resurgence of these devices is due to their ability to keep time, but also to give you your Heart Rate, your step count and so on. It was very very compelling to get one of these!
In fact, because we both own Fitbits, my brother and I have designed some motivational open source hardware jigs to help us boost our counts when we start lagging. We will be presenting this at a couple of different conferences as the design iteration progresses. Watch out this space for announcements!
But more to the point, wearing this device has taught me a number of things. I had that initial ramp up where my skin reacted to the device as if it is an allergy. Then, I got back to that problem of a certain portion of my hand looking lighter due to reduced sun exposure. Also, this particular device keeps track of my sleeping habits, and even though I suffer from insomnia, I do not like wearing this thing at night, because after about 16 hours or so, this thing does get irritating. And yet, I like the belt-buckle design, because I can remove it whenever I want. I am having a hard time envisioning a long-term, Velcro or adhesive backed device on me. But, I know, other people might react differently.
Look closer at the picture. Dust and dirt are another problem. (The scratches are from my cats showing me love, so there's not much a medical device can do there :) ) I hope you get the general idea. Wearing the devices yourself, whether yours, or a competitor's, or of someone else (I am not working on a wearable right now, but hey, if you are looking for someone...), helps you understand the underlying issues. And you know, this extends beyond just skin and wearables!
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References:
1. The 3M Article on Adhesives for Skin: https://www.mdtmag.com/article/2017/06/six-stick-skin-challenges-medical-device-engineers-must-understand?WT.mc_id=pr_MedTech_WearItWell_07/01/2017&WT.tsrc=Article
2. First image, courtesy, Pexels: https://www.pexels.com/photo/person-with-black-pedicure-raise-both-2-hands-218939/
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