In this episode, we talked to Bret Ludwig, Senior Product Development Engineer at 3M. We talk a wide-ranging conversation with medical skin tapes on applications, different types of adhesives to use in different situations, and skin trauma. Pretty much anybody who's looking to commercialize a wearable product shouldn't miss this because we cover all kinds of questions that are relevant to product teams.
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Steve: It's really good to have you on board, really appreciate you taking the time. And I guess, just to give you a quick introduction, Bret Ludwig, not to be called doctor, he who doesn't like it, but Bret Ludwig, Senior Product Development Engineer of 3M, PhD chemist by training, developing products at 3M for 25 years. And I'm really just kinda like lately living all the challenges with regards to sticking to skin and some of the applications there. And, of course, from a Tapecon perspective, it's exciting to have you on the podcast just because of what we're seeing in terms of new applications coming in in wearable, particularly on the skin. So welcome to the podcast. And I guess my first question is just tell us about yourself, 3M, your role at 3M Medical Materials and Technologies?
Bret: Yeah. Thanks, Steve, so much for the invitation to join you today. As you mentioned, 25 years at 3M developing products, got my PhD in Polymer Science from North Dakota State, in Fargo. So, when I moved to the twin cities in the southern half of Minnesota, I was actually moving to a warmer clim. That might be a surprise to some people who aren't familiar with the Upper Midwest. 25 years at 3M, started in the signage business, making materials that go into signs. Jumped from there to the abrasives business. And then, most recently, for the last six years, I've been in the Medical Materials and Technologies group, part of our Medical Solutions division. In those six years, I've primarily been developing solutions for stick to skin. And was hired into the group just as this concept of wearables came, started pounding on our door. And it didn't start with a knock, I swear. It went from nothing to a pounding. It's like the industry needs this. And it's been a very interesting six years. 3M overall, 30 billion-ish company, business groups within just about every country in the world. And products and services in just about every industry that you can imagine. Everything from computers, to smartphones, to healthcare obviously, to consumer products. When people think about 3M, they generally think about PostIt notes and scotch tape. That's our consumer business. Consumer is only actually about 15% of what 3M sells. Our vast majority of our sales go into other companies making products. And we like to say that you're never more than a few feet away from a 3M product because our materials are in pretty much everything you use. So we are everywhere. And what makes 3M unique is that, being in all of those industries, we have all of the technologies that support the products going in to those different businesses. And what makes 3M really unique is that, a business owns the product, but they don't own the technology. In my years in developing products at 3M, I've probably made use of probably 40 of the 51 different technologies that 3M claims they have world-class expertise in. And it's that ability to reach out across business lines and to use the expertise of developers in other industries to help us solve challenges for whatever we happen to be working on right now.
Steve: Yeah, and I always, every time I talked to someone from 3M, I'm always impressed with the level of job rotation and perspective that people get working in different business units. And when you look at the periodic table when I visited the innovation center up there, how technologies from one area can be applied to another, and I guess that's part of the innovation... I guess, with medical tape, and I listened to your previous podcast about the story of your time in abrasives and talking about the abrasive wheel challenge that you had. But I have to imagine that, while you come in, and working with medical tapes, that you're bringing some of the skillset and the technologies that you were exposed to in abrasives into medical tapes, right?
Bret: Exactly. Obviously I can't go into any detail on my newest projects, but I am using a couple of technologies directly from abrasives in trying to tackle what we think will be a future demand by the medical industry.
Steve: That's great. Well, let's start with, I guess, the basic question for anybody who just... What is a medical adhesive tape, I mean, for the foundations for some folks?
Bret: Yeah. So, foundationally, a tape, let's start with tape, is an adhesive, generally a pressure sensitive adhesive. I gotta take another step back. When we say pressure sensitive adhesive, we're not talking about the ultimate adhesion of the tape being dependent upon how hard you press. That pressure sensitivity is only at the moment of application. So, if you just take, say, a piece of scotch tape and lay it gently on a table, you can pick it up and it won't have adhered. If you put it on the tabletop and apply some pressure and then peel it up, you'll find that it had adhered. So, when we talk pressure sensitive adhesive, we're only talking about that initial moment of application. So it doesn't matter how hard you initially press, that's not going to determine your ultimate level of adhesion, it's only gonna determine how quickly you get to that ultimate level of adhesion. So there's a pressure sensitive adhesive tapes, regardless of their use, pressure sensitive adhesive, and some kind of backing. Now, backings range from films, to non-wovens, to possibly a woven backing. And in industrial markets, it could be a metal foil as the backing. And to say that a tape performance is dependent on the PSA and to stop there is so wrong on many levels. You can have the world's best adhesive for an application, but if it's on the wrong backing, the performance just will not be there. And so, going into medical and the importance of backing selection, the one that comes top to mind is actually, for sticking to skin, you want a backing that is conformable, can stretch some, and can move with the skin. One of my first projects when I joined Medical six years ago was taking a look at our silicone tape. A customer was trying to use it for an application that we'd never recommended it for. And we said this tape would stick for three days. Well, in their application, the way they were applying it, due to the conformability of the backing, it started lifting within three hours. So the initial back and forth was what is wrong with this lot of tape? It's not even sticking for a half a day. And eventually, we had to tell them, the backing of that tape is just not suitable for the application you want. And to wrap up this, the difference between a medical tape and an industrial tape is, since skin is a living, sensitive substrate, you need to reduce or eliminate as much as possible any irritants in the adhesive. So PSAs are made from polymers, polymers are made from monomers. And it's not the polymers that generally irritate skin, it's the residual monomers. And a medical adhesive has been processed in such a way to really reduce the level of monomer left in the adhesive, and thereby minimize the possibility of irritation to the skin.
Steve: Yeah, and just to get their vernacular down, like you refer to backing versus a liner, which is a different phrase, different level of construction.
Bret: Yes.
Steve: I'm interested in your comment on the liner. Because when you talk about slit liners or extended liners, what we've come across is you can specify the right adhesive, the right backing, get everything right that you described, but then also taking account the ultimate end-user's actual application of the wearable, you can actually... What you do with the liner is equally important, from printing instructions for use, or having that liner configured for how to apply it best given what area of the body. I guess can you comment on that?
Bret: Yes, absolutely. And here's where the different perspectives come in. In your industry, you're always thinking about the liner and then how to make it work for your end-customer. Whereas, for my side, on the adhesive development side, the only thing I want out of the liner is that it'll come off the adhesive cleanly every time. So, vernacular, the backing is what carries the adhesive. That's the top of the adhesive bandage that you put on your skin. The liner is the paper or polymer film liner that is on the adhesive and protects the adhesive during manufacture of the tape and during transport. And liners are typically films or paper coated with a silicone material that the pressure sensitive adhesives release easily from. And, as you said, there are as many varieties of liner as there are of adhesives. And knowing the full spectrum of adhesives out there, I can tell you, that as a lot of different liners. And matching the liner to the adhesive is just as important as matching the backing properties to the final substrate.
Steve: Yeah, and I appreciate your perspective on that because, I mean, there's a symbiotic relationship, I think, between 3M and Tapecon and that we're a converter partner. So, ultimately, we're both serving the ultimate end-user, specifying the right material. But those details of the actual end-use application is where the converter comes in and answers that, gets all those liner details kinda figured out. So appreciate that. It's interesting to hear that. But it's absolutely a team effort, I suppose, on that, from that perspective.
Bret: Yeah.
Steve: I guess moving on to my next question, which was about more like factors affecting skin adhesion, what are the various factors that affect skin adhesion?
Bret: Yes. As we've mentioned, I had a stint in abrasives, and when I came over to Medical, I really missed developing products from abrasives 'cause it was so easy relatively. If you're braiding a piece of stainless steel, it turns out, every piece of 302 stainless steel is the same. When it comes to skin, no two pieces are the same. It makes things much more challenging to develop products for skin. So some of the specific details on what makes adhesion to skin difficult. First of all, it's a rough surface. It may look smooth, but if you really zoom in, there's nooks and crannies and wrinkles to varying degrees. And so, the typical medical tape has one to one-and-a-half mils of PSA on it. If you are applying that to the skin, well, the valleys on the skin can be much deeper than one-and-a-half mils. So it's very difficult with a typical medical tape to fully wet out the skin. And that can reduce your ultimate level of adhesion. The skin is not necessarily clean when you apply something. Could be swept or oil naturally generated by the skin. Skin is an elastic material, an elastic substrate. So going back to my earlier comment about needing a tape backing that can move and flex with the skin, very important. If your backing can't move with the skin, every time the skin moves, there is a stress imparted in the adhesive. And it may not cause the adhesive to pop off the first time, but after repeated stresses, it's gonna lose eventually. Skin is also a low-surface energy adhesive. Sorry, low-surface energy substrate. For people in the automotive industry, they talk about sticking to LSE, low-surface energy substrates, on like plastic bumpers in that. And those might be polyethylene, high-density polyethylene. Again, the skin is tougher. Skin has a lower surface energy than polyethylene. There's the fact that the surface of the skin, the stratum corneum, is continually, that's the dry outermost layer of your skin, that's what you see flaking off. The rule of thumb is that the stratum corneum is being totally replaced every 14 days. So a very challenging substrate. And the last one, as my friend Kris Godbey, one of our application engineering aces, says, "Skin is a living, breathing substrate. And when you put something on it, it's gonna do whatever it takes to get rid of it." It might very well decide to itch. And itching is the skin's method of like getting you to unconsciously pick at and scratch away whatever is irritating it. So a living substrate, definitely the most challenging for adhesives.
Steve: Yeah, I know. I think sometimes people forget that the largest organ in your body is skin. And it's just so easy to not really, I guess, to just not really remember that. And you mentioned all the variables of the skin, but then all the extra variables that are uncontrollable, I mean, what a complex challenge? Because you've got the skin itself, which it has all these variables, and then, of course, the external environment. Water, as you mentioned, environments, everything, right?
Bret: And not only does skin vary from person to person, it varies dramatically from one part of a person to another part of the same body. So we'll talk more about that soon, I'm sure.
Steve: True. Yeah, well, I mean, obviously their core goal is to specify the right material for the right application. So let's talk about, I guess, what goes wrong when that goes wrong. So what are some of the types of trauma? When you get into trauma, what are some skin trauma that could be caused? What types of trauma can occur?
Bret: Yep. The first one that comes to mind generally is skin stripping. So there's multiple layers to the skin. I've already mentioned this, the stratum corneum, that's the outer most layer of pretty much dry dead skin cells. Layer below that is the epidermis. Cells are a little dryer. They're in the process of dying. And below that is the dermis. Skin stripping is when the cohesion in the epidermis layer is lower than the adhesion of the adhesive to the top of the skin. So, when you remove the tape, you remove one or maybe more layers of skin with it. And skin stripping is generally, the classic look for skin stripping is the skin looks moist after you've removed the tape, red generally, and moist, because you've gone down into the lower layers of the skin where there's more moisture. You can also tear the skin. And that's just generally, you see a rough incision, I suppose, might be a non-professional's definition of a tear. Other things, tension blisters. If you have a tape with an elastic backing, what you don't want to do is stretch it a little bit and apply it to the skin in a stretched condition. Because then you will always have, if it's an elastic backing, the backing will be pulling back. And that continual tension on the skin can cause the skin to blister at the edges, at the ends of the tape where the stress is being applied. And then, oh, there's maceration. Maceration is just a fancy word for skin being swollen by moisture. We've all experienced maceration. That's your fingers turning pruney in the bathtub. Under a medical dressing, it can swell to the point where you take off the dressing, the skin will just appear totally white. We want to avoid maceration in medical tapes and dressings because macerated skin is weaker skin. And therefore, if you have macerated skin, it's more likely to experience skin stripping when you remove the tape. And finally, going back to skin being a living substrate, there's allergic reactions, allergic dermatitis. The skin reacting to irritants, say, residual monomers in tape. And that's why we go to extra lengths to reduce the residual monomers and other irritants in tapes. And, finally, folliculitis. That's infection of pores on the skin. If you are wearing a tape for a long time, bacteria likes to multiply in wet, dark places. And underneath a tape or a medical device is generally wet and dark. So you can get infection of the pores in that situation.
Steve: Yeah, no shortage of potential failure modes, sounds like.
Bret: No shortage of challenges, nope.
Steve: And I remember seeing a presentation on internal wear studies and seeing a picture of someone's back, and all these pieces of tape, and numbered. And it obviously someone's doing something in the lab to kinda do the work required to kinda, I guess, circumvent these failure modes. So, I guess, can you speak to... And, of course, by the way, one of the things I've been impressed with also is just constantly pushing the envelope of wear time, now it's like 14-day, and trying to really get out and extend those wear times. But obviously, anytime you roll out a new product, as you know, in product development, there's a lot of validation that needs to take place in the design side before you're gonna launch a product. So just curious if you could maybe allow us to peek under the hood and just let me know how are those internal wear studies conducted, how do they go, and just what are some of the considerations while that's going on?
Bret: Yep. So yeah. Those pictures are from our formal internal wear studies, ruled by an Internal Review Board, the IRB, they make sure we don't harm anybody during the studies. We typically have from 12 to 20 people wearing tapes or mock devices for... Well, it used to be that a clinical study never went beyond three to five days, and were always one-by-three-inch strips of tape worn on the back. And that goes, most medical tapes were initially developed for hospital and clinic use, where a dressing in that type of situation wouldn't be on from typically more than a few days before they changed the dressing. So, in the traditional clinical studies, these strips of tape were applied to people's backs. And they were actually told, "Okay, while you're doing the clinical study, don't exercise, don't work up a sweat. And when you're in the shower, just shower facing forward. Do what you can to avoid getting those tapes wet." Well, that's all fine and good if you're developing a tape for hospital use. It's okay. And when I joined the medical group, we were told, "Okay, this wearables thing is coming down the pike, and we need solutions for this." Well, one of the first things we did was we got together with our clinical group and said, "Okay, this traditional clinical is just not gonna cut it anymore." Because people wearing medical devices, and my default go-to is always continuous glucose monitors, CGMs. People wearing a CGM aren't going to avoid exercising, and they're certainly not going to be able to keep it from getting wet when they shower every day. Oh, and it's not gonna be worn on the back. So, our first clinicals for developing longterm wear, we started, we put a plate on there about inch-and-a-half in diameter roughly. And instead of having people wear them on their back, we had them wear them on their chest, because that's where the cardiac monitors would be worn, and on the abdomen, because, six years ago, that's where most CGMs were worn. Actually felt a little bit guilty about asking our participants in the study to wear eight of these discs for two weeks. But it turned out that, when they came in to have the samples removed, two weeks later, that it really wasn't that much of an ask. A lot of them said they were looking forward to the next time they could earn a little extra money in a two-week study. And we learned, over the first few studies, we learned that we weren't really good at predicting what adhesives would last for 14 days. Of course, we had looked back at our decades of experience on stick to skin. And the various experts in Medical and our adhesive experts in the larger 3M all had their favorite for adhesive as so what they thought might last for two weeks. And turns out just about everybody was way off base. Can't go into details as to the key properties that we found were important, but most of the experts favorites were nowhere near. Because it turns out, what works great for three to five days, it's the duration on skin, there's different things happening. One of the things, one of the universal at this point, actually we're hoping to change this, but at this point, one of the universal truths about getting a device to stick to skin is, I mentioned, having about a one-and-a-half inch plastic disk standing in for a wearable medical device. So if you have the stick to skin tape go just to the edge of that, it will not last nearly as long as if you extend the stick to skin tape about a quarter of an inch all the way around. And our terminology for that is, the tape that sticks out beyond the device, we refer to that as the skirt. So a skirt, when you have that, now I kinda wish I had a sample on my arm so I could demo, but when you're wearing a device, well, I will share that you don't really have to worry about the sheer properties of your adhesive. The sheer properties of an adhesive are how you measure an adhesive's resistance to a long-term low force. Like you hang something heavy on a wall, and then gravity is always pulling that slowly down. Wearable devices generally have negligible weight. So you don't have to worry about sheer being their failure mode. Where wearable devices really get challenged is, if you're wearing them on the back of the arm, particularly, and you walk through a doorway, and you're really not cognizant of how often your arm brushes up against something until you're wearing one of these samples and you're bumping it against something multiple times a day. And that's where the challenge, that's where the stick to skin adhesive is really challenged, in these bumps and tugs, when the edge of the device encounters a doorway or gets caught on your clothing when you're getting dressed. It's the bumps and tugs that we need to protect against. And having a skirt just changes the physics of how the tape and skin are moving to greatly improve their resistance to those impacts. Yeah, it's interesting to hear about how people had their winners picked. So chalk went up for the scientific method for yet again eliminating or reducing bias and being a little bit more objective. So that's really good to hear. And you probably know, yeah, the skirt, that's a new concept for me, I never heard of it that way, so I appreciate that too. Biocompatibility, that was one thing I was just thinking about, is 'cause people listening to this are generally product teams, so people that are charged with launching a new product into the marketplace, and they've got a ton of considerations. Obviously they need some guidance to get through and specify the right adhesive, but there's also some regulatory hurdles that they need to get through. Can you speak to maybe some of the ISO standard for biocompatibility and how, I guess, at the lab scale, you're overcoming that and kinda getting through that to help some people just launch these products faster?
Bret: Yeah, so there's only so far that 3M can go in that, regarding that challenge. Of course before we launch a tape, we do the biocompatibility studies and make sure that our tapes and all of their components meet those requirements. However, Medical Materials and Technologies, the part of Medical Solutions division that I'm part of and that sells tapes to other companies making their medical devices, we sell our tapes non-sterilized and depend-upon our end-customers to, if it needs to be sterilized, they need to do the sterilization. We study our adhesives post-sterilization processes and make sure there's nothing really egregious. No egregious changes that take place in the adhesive and affect biocompatibility. But, of course, we can't test every sterilization process that an end-customer might expose our tapes to. And that is why the end-customer has to sterilize their tape and put it through any other processes that they are and make their final product and have that tested for biocompatibility as their responsibility. So we verify that the materials we provide are biocompatible. But it remains on the customer to make sure their final construction also meets those requirements.
Steve: Great. No, thanks. I'm leading to wrapping up, this will probably be my last question. But it's back to the focus on that product team and what they need to know to properly specify related things to get their product out there. So, I mean, obviously, you mentioned biocompatibility, we just talked about that, but what other questions should someone consider when developing wear on? I mean, there's gotta be a large amount of considerations. But, I guess, what would you say to a product team that's looking to launch on the types of questions that they should be asking to be able to help specify the right adhesive for their application?
Bret: Yep. First, the first questions that my good friend Kris Godbey gets asked by customers calling for a application support is, Kris will ask them, "Where on the body?" Because depending on the part of the body, that the skin varies. We would not recommend the same tape for a face application as we would for the arm. It's critical how long they want it to last. At this point, there is not a solution that is going to adhere a hearing device for three weeks and also removed gently with no guarantee of skin damage. At this point, you don't get gentle to skin and long-term wear with the same adhesive. We're doing everything we can to get there, but we're not there yet. So, if you want the device to stick for five to seven days, Kris is not going to recommend our 14-day tape, because, at 14 days, it's still going to be adhered too well and be too uncomfortable at removal. And we have other tapes that do just fine for seven-day applications. And, again, it's the how securely you need it adhered. If, say, you've got a one day application, well, is it one day on a baby, in a NICU? Well, in that case, you're gonna wanna use a silicone adhesive that will remove from the skin without damaging it. If it's a one day application for an NFL player who's holding a monitor on his body to measure his performance, you're not gonna use the silicone tape, you're gonna use one of our more aggressive tapes to do that. So some basic questions there. And the most important item I would leave with your end-customers and our end-customers is speak to us early. Too often, Kris comes to me with yet another story of someone who has developed the next great widget for wearable medical devices. And they've spent years developing the algorithms and the sensor and the casing and the electronics, and then only six months before they wanna start their final 410 clearance, do they come and say, "Hey, we need to stick this to the skin?" Please talk to us early. It'll save them heartburn and make our life a little easier, giving us a little longer runway to get them where they wanna be.
Steve: Yeah, I would, definitely. I echo that sentiment. I mean, I guess from a converter perspective, it's, do you want additional printing on it? What printing method? And then that's gonna play in. Or do we wanna laminate something else to it? Are we combining multiple materials? There's a lot of trends in towards what we're calling, which is electronic skin patches. I mean, to what extent do you want to potentially put some additional electronics or functioned into that patch? So, yeah, a lot of considerations, a lot of questions. And I think we both agree that the earlier, the better, engaging the raw material supplier on the science side as well as the manufacturing partner. So ends down there.
Bret: Yeah, that's boiling six years of experience down to 30 minutes.
Steve: Well, no, and we could go on, probably I'm sure, 'cause there's so many verticals you can go down in this category because we haven't even talked about... You look at the various markets, whether it's medical or nonmedical, as you've mentioned, with the reference to the football player, a lot of growing trends on the athletic space and just that consumer space, which is a lot different than maybe more of a business to business type play in a medical device. So it's really spans the gamut.
Bret: Yep. A lot of our wearable device customers come to us and they say, "We've got this wearable medical. But while we're waiting for approvals and clearance for the medical device, we're gonna do a consumer device in the meantime to generate some revenue and some experience for ourselves and manufacturing. So there's incredible overlap between consumer and medical in this space.
Steve: And I guess the beauty is, if you're a brand owner, I mean, you just get both of our companies on a conference call. Just a complete design review. I mean, that's it, I mean, it really can be a one-stop shop, you don't need to get passed around. Do you know what I mean? And really get all the people and all those perspectives on the table earlier in that project, which will lead to speed to market. Is that an accurate statement?
Bret: Yes. No, I've seen everything from, again, I bring her up all the time because she is the guru of the solutions, Kris, she's answering multiple calls a day and giving advice. And then the next step up is it might be a Kris and I and a couple of business people on the line or in a conference room with a customer, talking about options, and options right now, and then what we might have available in a year for our customer's second generation. I've seen it all the way up to, a customer brought in like four or five engineers, some of their leading business people, their product designer, and 3M brought to the table expertise from around the company, and just brainstormed for a day on the customer's design for this product. And at the end of the day, the customer said, "We're obviously working with the experts here at 3M, you just design this for us." And I guarantee you, this is not something that 3M does on a regular basis, so please, I ask people not to call 3M and say, "Oh, we hear that you design medical products." It's something that 3M will consider possibly doing for major customers. So, yeah, no, 3M really is all-in on the wearable medical space.
Steve: Well, Bret, listen, I really appreciate your time. I mean, tons of great information that I think can help a product team, factors to consider to get their product out there. So appreciate the time, expertise, the collaboration between our companies. So thanks for being on the podcast. And be well.
