Patients with circulation and blood pressure disorders rely on compression therapy to keep blood from pooling in unwanted places, but it’s notoriously difficult to apply and keep these special wraps in place. If they’re not tight enough, blood won’t return efficiently enough. Too tight, and you restrict blood flow. A team of engineers from MIT have developed a new compression wrap that tells you precisely how tight it is with the aid of color-changing fibers. Just match the color, and you’ll know the bandage is just right.
The structure of these pressure-sensitive wraps is no different than the ones used by patients all over the world. The team added strands of photonic fibers to the bandages, which change color as they stretch. Thus, a patient or caregiver can stretch the material around a limb, paying attention to the color of the fibers to reach the appropriate compression for a specific disease or use case.
The team created a chart that shows how much pressure the wrap exerts when the fibers are different colors. Red is the lowest pressure, indicating the fibers are not under stress. As they are stretched more, they become orange, then green, blue, and violet. Once the threads reach the correct color, patients know to stop tightening the wrap. They also serve as an ongoing indicator of compression bandage effectiveness. If the wrap loosens, the fibers will shift to warmer colors, allowing patients to tighten them to the correct level.
These fibers don’t require any power source to operate. They change color thanks to the internal structure, which changes as the fiber stretches. Each one is about a millimeter wide (10 times the diameter of a human hair), composed of ultrathin layers of transparent rubber materials. There are hundreds of these layers all rolled up lengthwise in each fiber. Light reflects off the inner surface of individual layers to produce the colors indicate pressure.
The changing color is a result of optical interference, the same process that produces colorful simmering on the surface of a soap bubble and on the feathers of certain birds. The team found these fibers could be tuned during production to change the color ranges. For example, you could design fibers that gauge pressure for other applications. Maybe you want red to indicate high strain and green to say everything is fine. That’s possible with changes to the fabrication process.
Currently, the fibers are costly because of the labor it takes to make them in the lab. The materials used are common and inexpensive, though. With an industrial operation, the team says the pressure-sensitive fibers would be “dirt cheap.”