Porcupine Quills Inspire New Medical Adhesives
In a prime example of turning to nature for inspiration, engineers in search of new biomaterials hope to emulate the unique penetration and binding properties of porcupine quills to develop new types of medical adhesives, needles and other medical devices.
Researchers at Massachusetts Institute of Technology (MIT) and Brigham and Women's Hospital in the US, write about their work in a paper published online ahead of print on 10 December in the Proceedings of the National Academy of Sciences, PNAS.
Co-senior author Robert Langer is the David H Koch Institute Professor at MIT. He tells the press in a statement:
"With further research, biomaterials modeled based on porcupine quills could provide a new class of adhesive materials."
"We believe that evolution is the best problem-solver," adds Jeffrey M Karp, the other co-senior author, and an associate professor of medicine at Harvard Medical School and co-director of the Center for Regenerative Therapeutics at Brigham and Women's Hospital. Porcupine Quills Anyone unfortunate enough to be on the receiving end of a porcupine quill knows that once they go in, they are nigh on impossible to remove.
For inspiration, the team turned to the North American porcupine, whose back is covered with around 30,000 barbed quills to defend against predators. Each quill is several centimeters long and ends in a four-millimeter tip covered in microscopic barbs. It is the tip that fascinated the researchers.
They made artificial devices with the same mechanical properties as the quill tips to see how best to exploit their ease of entry and difficulty of exit.
For example, by exploiting the mechanisms that make it easy for the quills to penetrate skin, it might be possible to design less painful needles for use in medicine.
And, by exploiting the properties that make quills difficult to remove, it might be possible to design adhesives that can bind internal tissues more securely. Current Adhesives Not Satisfactory The medical world needs more effective adhesives. For instance, patients who have had gastric bypasses or other kinds of surgery in the gut have their incisions sealed with sutures or staples, which can leak and cause complications.
And while doctors can sometimes use a type of medical superglue to bind tissue together, these can be toxic or cause inflammation, explains Karp. The Barbs Ease Entry as Well as Make Removal Difficult In their study, the researchers describe for the first time the forces needed for the quills to penetrate and exit the skin.
They were surprised to find quills with barbs required 60 to 70% less force to penetrate muscle than quills without barbs.
On closer examination, they found that as the quill goes into tissue, the barbs localize the penetrating forces so they tear easily through tissue fibers. This is much the same way as a serrated knife knife cuts more cleanly through the skin of a tomato than a straight-edged one.
But when you try to pull the quill out, the barbs open out and act like anchors, resisting the forces applied. The researchers calculated that the force required to pull a quill out of muscle tissues was about four times greater than that required to pull out a quill with no barbs. Experimental Adhesive Patch The team then made and tested an experimental adhesive patch with barbed quills on one side.
They had to apply 30 times more energy to remove the patch than they did with a control patch with quills but no barbs.
In their paper they also describe how to fine tune the artificial "quill" so it not only goes in easily, but also comes out easily. This could be used to help design less painful needles for injections, they suggest. Versatile and Universal Application In 2008 it was Langer and Karp who introduced the idea of gecko-inspired medical bandages. But, as Karp explains, they "require a reactive glue to adhere to wet tissues, while porcupine-quill-inspired adhesives attach to tissues beautifully without requiring the use of reactive chemistry."
"They are extremely versatile and potentially universal in their application," he says of the quill-inspired materials.
The team is now trying to discover if it is possible to make biodegradable adhesives on the quill principle. The idea is so they break down harmlessly in the body when they are no longer needed.
Funds from the National Institutes of Health, the American Heart Association, the National Science Foundation and the National Research Foundation of Korea helped pay for the study.