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Photonic Fibers Change Color When Stretched | To Show Pressure Level

[Estimated read time: 3 minutes]
  • The new photonic fiber could serve as a continuous pressure sensor.  
  • It’s fabricated from thin layers of transparent stretchable materials.
  • These multiple layers reflect light, producing different colors. 
  • It could be used in compression bandage to monitor pressure levels. 

Compression therapy is used to increase blood flow activity in the lower limbs by gently applying pressure to the ankles and legs. It gradually stretches out vein walls and increases the overall blood circulation, which reduces swelling.

Typically, a compression bandage or stocking is tightly wrapped around the affected limb. However, it’s hard to monitor how much pressure these bandages/stockings apply on the limb.

MIT engineers have found a solution to this problem; they’ve built photonic fibers that serve as continuous pressure sensors. It’s shaped into a compression bandage. These fibers change color when you stretch the bandage.

How It is Useful?

Patients or caregivers can use a color chart to stretch the fiber until it shows a color of a suitable pressure. It will help them to effectively wrap the bandage with optimal pressure level around the leg.

In medical conditions, like venous ulcers — which affects millions of people worldwide each year — it’s crucial to use the bandage or stocking at the right pressure. This is where photonic fibers fit in. These fibers reflect colors that could be easily distinguished by the human eye. It can tell you about the level of pressure exerted by a bandage, without having to use any additional device.

How It Changes Color?

Courtesy of researchers

The fiber is fabricated from thin sheets of transparent stretchable materials. The material is rolled up to form a jelly-roll-like shape, and each roll layer has a thickness of a few hundred nanometers.

In this unique structural configuration, each interface between individual layers is reflected by light. Since there are multiple layers of constant thickness, the light reflects each layer, strengthening specific colors of the visible spectrum, like blue, while reducing the other colors’ brightness.

Thus, the color of bandage you see depends on the layers’ thickness within the fiber. The color persists as long as the shape is maintained.

More specifically, the design of the fiber relies on light interference, in which transparent thin sheets reflect light, generating vibrant colors based on geometric parameters of layer and composition of material.

The color can be tuned by changing layers’ thickness. This requires standard optical modeling methods configured for special fiber design. For instance, fibers can be customized to reflect green color to show optimal strain, and red for alarmingly high strain.

Optical micrographs showing strain-dependent color of a fiber

Reference: Advanced Healthcare Materials | doi:10.1002/adhm.201800293 | MIT

The researchers stitched these photonic fibers along the length of compression bandage. Then they drew a color chart to determine the correlation between fiber strain and color.

They tested the effectiveness of this bandage on more than a dozen volunteers. They found that the volunteers were able to interpret fiber colors and apply corresponding pressure using a color chart.

The results indicate that the photonic fibers could enhance the efficiency of compression therapy, leading to less duration of treatment, improved patient outcomes and billions of dollars saved in the healthcare system.

What’s Next?

The existing photonic fibers are only a few inches long. Scientists plan to scale up the process of fiber fabrication. In coming years, they will be producing kilometers of such fibers, which will help them to bring its cost down.

Read: An Optical Circulator That Directs Light Without Using Magnets

In the future these fibers could be used in sports shoes and athletic apparel to indicate certain things like strain on muscle during workouts. Moreover, it could be utilized as remotely readable strain gauges for scientific tools and machinery, and in other smart wearable technologies where repetitive and high deformations are required.

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