Slug-inspired surgical glue
If you’re having an operation, or need a wound closing, you may be given a medical adhesive in order to help you mend. But according to research out this week, current adhesives have some major limitations, which could impact the success of a procedure. Cyanoacrylate - or Super Glue - for example doesn’t do well with wet surfaces, a problem when it comes to surgery. Doing its job as the body moves is also a challenge, and other adhesives’ sticking power isn’t all that strong. So what can be done to improve these properties? This week Harvard University have announced an adhesive that’s stronger and better able to cope with these wet and dynamic conditions. Katie Haylor spoke to Dave Mooney about the project’s rather slimy inspiration...
Dave - These slugs have developed a type of mucus that allows them to adhere very, very strongly to a variety of different types of surfaces, to do it in the presence of water and other fluids, and were very flexible and allowed a lot of dynamic movement. So the slugs had solved some of the key issues that we’re looking to address. While we’re not attempting to mimic how they do it in terms of there’s no mucus from slugs in our devices, we use them as inspiration for how one could try to design better adhesives.
Katie - Please tell me you had some slugs sitting around in your office which you were watching diligently?
Dave - Only fake ones unfortunately. We don’t do any actual research with slugs. A variety of scientists have been studying slugs for decades trying to understand their mucus and it’s properties and so we learned from all that science that had been done before.
Katie - Tell us about your product then - talk me through the chemistry?
Dave - There’s two key features to this concept for a new type of medical adhesive. The first is that you want to have a very strong chemical bonding to whatever you’re trying to adhere to. The other feature that we combine with this though is a material that can absorb and dissipate a lot of forces or stresses - an analogy might be here a shock absorber on your car. Here the adhesive both sticks really strongly and can absorb a lot of stresses so they don’t get felt at the interface and don’t cause the adhesive to peel off or fail.
Katie - Would this be someone stretching because they’ve recovering from a wound and they’re getting more mobile, or if someone moves around on the operating table? Is it those sorts of movements you’re trying to build in inherent flexibility in your adhesive to cope with?
Dave - Partly those types of movements and other movements that are naturally coming, for example, from different organs.
Katie - Back to the chemistry then, talk me through how you achieve this strong bonding?
Dave - We achieve the strong bonding by having long molecules that have a high density of positive charges. The key feature here is that tissues and cells in our body are overall negatively charged, so the positively charged molecules in our adhesive want to interact with the tissues and cells in our body. Then we provide the right chemistry so the the positively charged entities on our adhesive can chemically bond and form stable what are called covalent bonds with the underlying tissue and cells.
Katie - You mentioned this first layer, but what about the second layer - this ability of the material to absorb energy?
Dave - We have a what’s called a hydrogel, which is a long polymer molecules that are swollen in water. The positively charged molecules bind both to the underlying tissue, but also bind to this hydrogel. You can think of it as being somewhat squishy and has the capability of deforming very readily and, as it’s deformed, it can absorb and dissipate all these stresses or forces that the adhesive might get subjected to from the surrounding tissues.
Kate - Tell me, when you tested this in animals, which you have, what have your found?
Dave - We can use this to adhere medical devices to beating hearts, for example, pig hearts and have a very strong and stable adhesion that simply was not possible before. We can seal holes in tissues, for example, the heart or other tissues and have those prevent any type of bleeding or leakage of fluids. We can use these as a means of stopping bleeding on, for example, a lacerated liver. And it’s possible to use these on the skin, for example, as an adhesive and an agent to promote wound healing.
Katie - Why do you think this new product is important - in what ways is it important for surgery?
Dave - One is is enables new capabilities that we simply did not have before. For example, if we have a device we want to put on a beating heart, the current adhesives simply don’t allow you to stably adhere this type of device. Then we can also achieve some of the similar functions of the current adhesives but do much better.