The pads on the toes of a gecko are coated with microscopic hills and valleys, which help the lizards to cling to difficult-to-climb surfaces. With this in mind, researchers have created a sticky, strong, biodegradable surgical adhesive bandage that could be used in a variety of medical applications.
Jeffrey Karp, one of the authors of the paper published in the Proceedings of the National Academy of Sciences, talks with guest host Joe Palca about taking design tips from lizards.
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JOE PALCA, host:
And now from a bit of basic biological research to a little bit of bioengineering.
Lizard feet and the operating room may not seem to have much in common but for years, scientists have been fascinated by the way geckos are able to walk up walls and across ceilings held on by tiny textures on the pads of their toes.
Writing this week in the journal, Proceedings of the National Academy of Sciences, researchers describe how they've taken those toe structures and use them as inspiration for designing the surface of a surgical bandage. The team hopes that the bandages could be used to replace sutures, stitches in the operating room.
Joining me now to talk about this work is Jeffrey M. Karp. He's the director of the Laboratory for Advanced Biomaterials and Stem-Cell-Based Therapeutics in the Harvard-MIT division of Health Sciences and Technologies. He's also in the Department of Medicine at Brigham & Women's Hospital and the Harvard Medical School.
Any other titles that I've left out there?
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Dr. JEFFREY M. KARP (Director, Laboratory for Advanced Biomaterials and Stem-Cell-Based Therapeutics, Harvard-MIT Division of Health Sciences and Technology): Oh, I think you got them all.
PALCA: Okay. That's excellent. Thank you. Welcome to the program.
Dr. KARP: You know, it's a pleasure to be here.
PALCA: Well, okay, so, you know, one of the things that I've been - looking at the pictures and the article, it's a little unusual to think that simply the surface structure of something is what makes it sticky but I guess maybe we have rethink or become educated about what stickiness means.
Dr. KARP: Yeah. It's remarkable how geckos are able to walk up the wall and, you know, hang from a single foot. I think people for years thought that the gecko must have some type of glue on their surface and during the last seven or eight years, people have elucidated the mechanisms and it turns out there's absolutely no glue on the surface, but that they have this hierarchal structure ending in these nano-pillars. And the nano-pillars make these typically insignificant interaction between two surfaces significant such as Van der Waals interactions and capillary forces.
PALCA: Whoa. Van der Waals interactions. Now, remind us, for those of us whose physical chemistry was a few years further back. What are…
Dr. KARP: The easiest way to think about it is any molecule at a certain point in time may have a buildup of positive charge on one side and negative charge on the other. And when these tend to line up, they can cause forces of attraction.
PALCA: I got it. So it's - but it's a molecular kind of attraction. And I was thinking that Velcro was sort of a larger structured version of things that are not sticky but stick together very well. But I guess this is more on a molecular level?
Dr. KARP: Yeah, exactly. It's almost, you know, completely different mechanism, whereas Velcro is a mechanical interlock mechanism that doesn't rely so much on these other types of forces, but the gecko has evolved to be able to use just millions of these nano-pillars to increase the surface area of contact and make the Van der Waals forces and capillary forces which are typically not significant, significant.
PALCA: By the way, if you'd like to join this conversation about the gecko-based or gecko-inspired surgical bandage, give us a call at 800-989-8255, that's 800-989-TALK.
So what was the challenge here to recapitulate this design in something that could be put into a living person or what was the big challenge?
Dr. KARP: Well, I think, you know, initially, we weren't even thinking about the gecko. We recognized that there was really a big need for biomedical adhesives, for internal applications that were tape-based, so something like the equivalent of an internal band-aid. And you know, we surveyed the literature, we looked at what was available in the clinic and we quickly realized that many of the glues just don't have strong adhesion. And the ones that do, such as the medical-grade crazy glues, elicit a very strong inflammatory response.
And so we began thinking, you know, how can we apply what's out there to create the next generation of medical adhesives and we decided that chemistry was going to be really important because you could use it to crosslink to tissue to obtain very strong bonds. But we wanted to minimize that inflammation, so we thought, you know, then it occurred to us that geckos have this amazing ability, people were just elucidating at the time these types of mechanisms. And we thought, well, if we include types of morphology that the gecko uses on the surface of our - adhesive tapes, maybe we could reduce the requirement for chemistry and obtain strong adhesion.
PALCA: So these tapes, what are they made of?
Dr. KARP: So it's a great question. We had to create a completely new material because, you know, our thought was, the material - if we're going to make a tape, we want it to conform to the surface of a variety of different tissues. And tissues can have very irregular morphologies. So we designed a brand-new polymer or plastic that was biocompatible, biodegradable and had elastic properties so we could actually, you know, pull it and it'll elongate two to 300 percent. So we first - that was the very first thing that we did.
PALCA: Wow. And - it's interesting, though, people don't typically think of plastics as biodegradable. Is it because of the microclimate inside the body where it's acidic or their enzymes are - why is this plastic breaking down when others don't?
Dr. KARP: So, well, we just include ester groups which can be hydrolyzed by water and then in the case of, you know, acidic or basic conditions, this can either increase the rate of degradation. And further more, there are a variety of enzymes that cells can produce like neutrophils or monocytes which can speed up the degradation rates.
So, you know, we're in an era now where there's a variety of different biodegradable polymers that have been approved by the FDA or in the clinic. And the best example is degradable sutures.
PALCA: Really? And one of the things that, I guess, these are different from gecko - the properties that geckos have is the geckos usually do best on - as I understand it, on a dry, smooth surface, but you're talking about materials that adhere to a messy, wet surface.
Dr. KARP: Yes. So geckos, about the pillars that the geckos have are made out of keratin which is a fairly hydrophobic material and thus it's believed that it can actually push water out of the way so it can interact specifically with surfaces. People have created a variety of different gecko-mimicking adhesives. But one of the greatest challenges in the field is that they tend not to work very well under wet conditions. In fact, what happens is they end up interacting with the water and not the surface.
So we had to - instead of just mimicking how the gecko works, we had to go beyond this and actually coat a very thin layer of a glue that we created that would not only bond to the tissue but would bond strongly to the surface of our adhesive.
PALCA: Well, let's take a quick call now and how about if we go to David(ph) in Scottsdale, Arizona.
David, welcome to SCIENCE FRIDAY.
DAVID (Caller): Hi. Thanks for having me.
DAVID: I had question about this because I remember reading about this when I was in high school, a gecko tape. And at the time, they thought it was something completely different - almost like Velcro on a microscopic level. I'm just wondering if the professor or the doctor knew - has the research been updated. Have they been making new discoveries about this or is it just now getting more attention?
Dr. KARP: Yeah. That's a great question. And in fact, people have now elucidated a completely different mechanism, in fact, if you take a gecko and place it on a completely flat surface, there's absolutely no mechanical interlocking that is occurring and it's all to do with the Van der Waals interactions and capillary forces. And just to - I'm sorry?
PALCA: No, go ahead.
DAVID: All right. Go ahead.
Dr. KARP: I was just going to say that the capillary forces are particularly interesting because when you take these dry adhesives and you actually reduce the humidity in the environment, the adhesion ends up going down. So this is one of the key demonstrations that humidity or a monolayer of water on a surface can actually enhance - significantly enhance the level of adhesion.
PALCA: David, thanks very much for that question.
We're talking with Jeffrey Karp about a new surgical tape that is based on how a gecko holds onto surfaces and can hold on very tightly.
I'm Joe Palca and this is TALK OF THE NATION from NPR News.
So Jeffrey Karp, how far along are we in the development of this, I mean, is this something that you're - it might go into patients in the foreseeable future?
Dr. KARP: Now, we sure hope so and we believe it has a lot of potential to help improve the lives of many patients, to decrease complication rates. We've tested this now - the model in the laboratory we used was a pig intestine tissue as it's very thin and reproducible so we initially screened a wide variety of different morphologies and chemistries, and then we ended up placing this into the peritoneal cavity or the abdomen of a rat and demonstrated significant cumulative effects of chemistry and morphology on adhesion. And so the next step for us really is to target specific applications and then try to, you know, move this into the clinic.
PALCA: All right. Let's take another call now and go to Chuck(ph) in Phoenix, Arizona.
Chuck, welcome to SCIENCE FRIDAY.
CHUCK (Caller): Hi. Thank you very much. My question is that is this: How does the gecko let go? And does the bond of the gecko's foot - is it very, very strong? Does he have to pull hard to let go? Or is there some way he just releases it? And that's my question.
PALCA: Okay, interesting.
Dr. KARP: That's a superb question. And that's actually something that I have an answer for because other scientists have just figured this out within the last couple of years.
So geckos have not only they have these nano-pillars but the pillars are in the shape of triangles. And so, you know, this just, you know, people at home want to try this, if you take a piece of tape and you cut it in the shape of a triangle, you try to peel at the point of the triangle versus the base of the triangle, the widest part, it's much more difficult to peel at the widest part than it is at the point. And so the gecko makes use of this principle which we refer to as contact line splitting. So what it does is it has all of the triangles essentially are pointed down towards the ground, so when the gecko wants to hang on the wall, it's the base of all of these triangles on the nano-pillars which is allowing them to adhere and not de-adhere and fall off the wall. But when they want to start walking, they simply lift from the point of the triangles, which is the easiest point to start peeling from, and then they can essentially de-adhere.
And that's another essential thing that I think, you know, I need to point out is that our strategy is more inspired from the gecko than we are mimicking the gecko because this very property - we don't think would be very useful in the clinic. We think the surgeons would want to be able to put this adhesive in and have it stay there and not move over time.
PALCA: Okay. We have time for one more really quick question and I'll give it to Edward(ph)in River Falls, Wisconsin. A quick question please.
EDWARD (Caller): Hi. Thanks for taking my call.
EDWARD: In using this tape as a suture, is it possible to include some kind of antibiotic or some kind of protein to speed the healing process as it dissolves?
PALCA: Wow, interesting. What about it, Jeff?
Dr. KARP: Yeah, absolutely. So we've designed this polymer so that it can be - we can actually tailor the degradation products and - tailor the degradation rates - sorry - and we can incorporate drugs such as antibiotics, anti-inflammatory agents or even growth factors to promote healing. So we think that, in addition to using this, to seal wounds, or bring tissues together, this could be the equivalent of a transdermal patch which is typically a part on the skin, the equivalent for internal procedures. And now we have a drug delivery patch that can be applied to nearly any internal tissue.
PALCA: Excellent. Great story. We're very glad we were able to hear about it. Thanks very much for coming on the program.
Dr. KARP: Oh, thank you for inviting me.
PALCA: Jeffrey Karp is the director of the Laboratory for Advanced Biomaterials and Stem-Cell-Based Therapeutics in the Harvard-MIT Division of Health Sciences and Technology. He's also in the Department of Medicine at Brigham & Women's Hospital and at the Harvard Medical School.
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For NPR News in New York, I'm Joe Palca. Transcript provided by NPR, Copyright NPR.