Smart fibers change color to show bandage pressure
When a patient is suffering from a condition such as venous leg ulcers, that limb needs to be wrapped in a compression bandage in order to stimulate blood flow. It's very important, however, that the the correct amount of pressure is applied. New color-changing bandage fibers have been designed to ensure that caregivers get it right.
Created by an MIT team led by assistant professor Mathias Kolle, the pressure-sensing stretchable photonic fibers have been woven into traditional compression bandages.
Each fiber is approximately 10 times the diameter of a human hair, and is made by rolling ultrathin layers of transparent rubber around an elastic core filament, to create a jellyroll-like structure. Ambient light shines down into that structure, and is reflected back by each interface between layers. Depending on how thick those layers are at the moment (which is determined by how much the fiber/bandage is being stretched), the light reflected by their combined interfaces will appear as a different color – this is due to a phenomenon known as optical interference.
Users consult a color chart, to see if the present color of the fiber indicates that the bandage is too loose, too tight, or just right. They can do so both when initially applying the bandage, and also to check it over time, to see if it needs adjusting.
In a test of the technology, a group of students applied three types of bandages to one another's legs – they used a plain bandage, a bandage with the photonic fibers, and a bandage in which printed rectangles stretch into squares when the amount of pressure is correct. It was found that the bandage with MIT's fibers made it easiest to apply the optimal pressure.
The researchers are now working on scaling up the production system, which is presently complex and results in fibers that are only several inches long. "Currently, the fibers are costly, mostly because of the labor that goes into making them," says Kolle. "The materials themselves are not worth much. If we could reel out kilometers of these fibers with relatively little work, then they would be dirt cheap."
Not only could the fibers be used in compression bandages, but they might also conceivably find their way into products such as athletic wear that changes color to indicate muscle strain, or strain gauges that could be applied to machinery.
A paper on the research was recently published in the journal Advanced Healthcare Materials.