Light propagating through an optical fibre

Stretchable optical fibre can deliver light pulses to brain cells

Image credit: AZToskhov

American researchers have developed a biocompatible and stretchable optical fibre that could be implanted into a human body to deliver therapeutic pulses of light or sense symptoms of disease.

The fibre, described by the team from the Massachusetts Institute of Technology as like a rope of liquorice, is made of a hydrogel which mostly consists of water.

Due to its flexibility, the fibre could be inserted into the body without causing any restrictions or breaking as the person moves.

In an article published in the latest issue of the journal Advanced Materials, the researchers describe how the fibre could in future deliver light impulses to the brain. A discipline known as optogenetics has been experimenting with the approach over the past decade to control activity of neurons; however, the researchers were using solid fibres, which could cause damage to the soft brain tissue.

The researchers tested the optical fibres’ ability to propagate light by shining a laser through fibres of various lengths. Each fibre transmitted light without significant attenuation, or fading. They also found that fibres could be stretched to over seven times their original length without breaking.

In further experiments, the team was able to demonstrate the fibre's ability to signal when it was being stretched.

They first loaded a fibre with red, green, and blue organic dyes, placed at specific spots along the fibre’s length. Next, they shone a laser through the fibre and stretched, for instance, the red region. They measured the spectrum of light that made it all the way through the fibre, and noted the intensity of the red light. They reasoned that this intensity relates directly to the amount of light absorbed by the red dye, as a result of that region being stretched.

In other words, by measuring the amount of light at the far end of the fibre, the researchers can quantitatively determine where and by how much a fibre was stretched.

“When you stretch a certain portion of the fibre, the dimensions of that part of the fibre changes, along with the amount of light that region absorbs and scatters, so in this way, the fibre can serve as a sensor of strain,” explained graduate student Xinyue Liu, who worked on the project together with Associate Professor Xuanhe 
Zhao.

The researchers imagine that such stretchable, strain-sensing optical fibres could be implanted or fitted along the length of a patient’s arm or leg, to monitor for signs of improving mobility.

Zhao envisions the fibres may also serve as sensors, lighting up in response to signs of disease.

“We may be able to use optical fibres for long-term diagnostics, to optically monitor tumours or inflammation,” he said. “The applications can be impactful.”

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