In this 21st Century Chemist profile, Purdue University materials chemist and marine biologist Jon Wilker explains his work: creating a new synthetic glue by mimicking the molecular structure of the sticky substance secreted by mussels and oysters. A glue that works in wet conditions could be of particular use in surgical medicine.
Glue With Mussels: Purdue Chemist Synthesizes Wet-Set Adhesive
TOM COSTELLO, reporting:
When Jon Wilker's not fixing cars, jogging around town, or deep sea diving, he's here in his lab at Purdue University studying mussels and oysters and how they do what they do: stick to things underwater.
JON WILKER (Materials Chemist, Purdue University): See how you have this cluster of them all stuck to each other?
WILKER: So one of the reasons that we study mussels and barnacles and oysters is they produce interesting materials. So, for instance, if say a mussel wants to stick itself to a rock what it will do is it will secrete an adhesive material.
This guy here is stuck to this guy so if a predator like a seagull or something wants to come by and pull one of these out of the crowd, because it's stuck to all the other animals then it's harder for the predator to get at it.
COSTELLO: Wilker is a materials chemist funded by the National Science Foundation trying to invent a breakthrough adhesive: a synthetic glue that works like the substance oysters and mussels secrete.
WILKER: If you think about most of the adhesives that you buy at the hardware store, they don't set under water. If you want to glue two things together usually you do that and the first thing you have to do is wait for the adhesive to dry out.
COSTELLO: An adhesive that could adhere to and bind wet surfaces would have the greatest potential impact in medicine - especially surgery.
WILKER: So we're hoping there’s some significance in our research. So, for instance, as we learn how nature makes materials, we can then use that information to develop application such as surgical adhesives and bone cements.
COSTELLO: Surgical adhesives that could be an alternative to stitches, or sutures, which Wilker notes, are actually a fairly primitive way to close wounds or surgical cuts.
WILKER: So, if you think of, for instance, sutures, right? You might bring together some soft tissue maybe skin but then you have to poke holes into the healthy tissue in order to tie things together. And so first of all, it's traumatic to the healthy tissue. Secondly, that creates, um, a bunch of sites that could increase the chance of picking up an infection.
COSTELLO: Sealing wounds or cuts with adhesive would be less damaging to the body. Inside the laboratory, Wilker and his team analyze the sticky substance made by mussels. Why not simply harvest the natural material for use as an adhesive? Well, only a small amount of the sticky substance can be isolated from each mussel.
WILKER: There’s really not much material there at all, tiny, tiny amounts. So, if you wanted to say, to isolate a gram of this adhesive, you need about 10,000 mussels.
COSTELLO: Wilker and his team need to synthesize a similar substance to get an adhesive that could be mass-produced and tailored for specific uses. And that means engineering a synthetic material that mimics the chemical - the molecular - structure of what the marine organisms produce.
It's a little like trying to duplicate a stack of wood blocks with plastic blocks. There's a limit to how much wood we can get from nature, while today, plastic blocks can be made cheaply, in large number. But to most closely mimic the stack of natural materials, the synthetic pieces have to be the same shape as the wood blocks and stack the same way.
WILKER: So what we will do is learn how to combine molecules for instance, into a polymer.
COSTELLO: Polymers are long chain-like molecules composed of repeating monomers, small molecules, linked, or bonded, together in a pattern like a wallpaper motif. Synthetic polymers are common building blocks for new materials. They’re what make up most plastics.
WILKER: We isolate those materials after we do the synthesis and then with those materials, those new materials that we just made, those we can then assess the bonding capability.
COSTELLO: Since this new synthetic adhesive has the same chemistry as the naturally occurring adhesive that mussels make underwater, it can be engineered to set when it's wet.
WILKER: That's a really, really difficult thing to do with synthetic materials.
COSTELLO: The synthetic adhesives not only work to bond materials in wet conditions, they can be engineered to create bonds of different strengths and to bond different materials: metal to metal, bone to bone. In the lab, they use samples of pig bone.
WILKER: We can take them on to the instruments in the other room and pull 'em apart.
GRADUATE STUDENT: Yeah.
COSTELLO: A materials testing machine then measures the bond strength: the units of force, or newtons, it takes to pull the two materials apart.
GRADUATE STUDENT: There's the breaking point. Make a note. 549.66 newtons
WILKER: Some of these things actually adhere really quite well. So, for instance, we have some polymers that are modeled after mussel adhesive and these adhesives actually can bond surfaces together strongly as superglue. So we have very high strength adhesion from mimics of the biological materials.
COSTELLO: Wilker hopes his synthetic adhesive can be developed into a new bio-based bone cement for use in orthopedic surgery to set broken bones, affix metal supports and plates, in some cases, doing it without screws.
WILKER: At this stage, we certainly don't have any products that are out there, but we’ve got, we’ve got some materials that are exhibiting a lot of promise for eventual applications development.
COSTELLO: Setting the stage for future advances in chemistry, discovery of new materials, invention of new products.
WILKER: The percentage of things in the universe that we know is tiny compared to what we don't know and even beyond just learning about what's out there, you have the opportunity to make new things.
Inspired by slug slime, scientists have developed a flexible adhesive that sticks to wet surfaces. This stretchy glue can be attached to a beating, bleeding heart and could someday replace stitches in wound repair.
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