Using pulses of light to stimulate cells in the brain, an emerging field known as optogenetics, has some real potential as a form of therapy. Reversing blindness, blocking pain and resetting our biological clocks are just a few areas where this technique could prove useful, but due to the mushy contents inside our skulls, scientists have to be very careful about what they use as a light source. A soft, stretchy optical fiber developed at MIT working with researchers at Harvard University appears to be quite a promising candidate, and could possibly even act as a warning light for diseases in other parts of the body.

The fiber is made from hydrogel wrapped in polymer and is said to be as bendable as a rope of licorice, yet robust enough enough not to be broken down in the body. The researchers say that these attributes mean it could serve as a long-lasting implant that provides long-term stimulation or therapy, without damaging the surrounding tissue.

But the optical fiber might do more than just harmlessly blast brain cells with light. After finding that their fiber could be stretched over seven times its length without breaking, the researchers began to experiment with its optical properties to see if they could reveal when and where it was being stretched.

The team loaded up different sections of the fiber with red, green and blue dyes, shone a laser through its length and stretched out the red section. By analyzing the intensity of the red light that made it out the other side, the team says it can determine which part of the fiber was stretched and by how much.

"When you stretch a certain portion of the fiber, the dimensions of that part of the fiber changes, along with the amount of light that region absorbs and scatters, so in this way, the fiber can serve as a sensor of strain," says MIT graduate student Xinyue Liu.

The fiber could one day be used as an implantable or a wearable strain gauge and could be applied to the length of a patient's arm or leg to track mobility after an injury, for example. Or if inserted in the right way, it could even be used to reveal early signs of disease through inflammation and the monitoring of tumors.