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Biodegradable polymer may replace glass optical fiber for medical applications


[Image above] A view of light delivery through a citrate-based optical fiber. Credit: Dinging Shan; Chenji Zhang; Penn State University

Optical fibers are used in a number of industries. The computer and telecommunications industries use them to transmit data. The medical industry uses optical fibers to transmit light to probe inside the body.

The success of many invasive medical procedures depends in part on a doctor’s ability to look deep into organs and tissues to view tissue damage or diagnose diseases. This typically involves sending light through a glass optical fiber implanted in the patient.

Unfortunately glass optical fibers have their limitations, as they are fragile and can break inside the organ or tissue if they bend too much. Glass optical fibers also are not biodegradable.

But a collaboration between researchers in the biomedical engineering and electrical engineering departments at Pennsylvania State University may provide medical professionals with a flexible optical fiber that delivers light into the body for viewing tissue and that also degrades in the body after use.

“The problem is that visible light can only penetrate to a certain depth, maybe hundreds of microns,” biomedical engineering professor Jian Yang says in a Penn State news release. “Near infrared light might be able to penetrate a few millimeters to a centimeter, but that is not enough to see what is going on.”

Optical fibers (fiber optics) are thin hollow rods of glass that carry light from one end to the other. Light particles travel through the rods and reflect off of one another inside the core as they move through. The cladding—the outside of the core—reflects the light particles as they bounce off the inner walls, keeping them inside.

Credit: Groman123; Flickr CC BY-SA 2.0

Instead of glass, Yang and collaborator Zhiwen Liu, electrical engineering professor at Penn State, developed a step-index optical fiber using a citrate polymer as the base material. This is a type of optical fiber where the core and cladding have different refractive indexes—the cladding having a lower index. This ensures that additional light doesn’t enter the tube and interfere with light passing through the optical fiber and prevents light inside the tube from escaping. Yang’s team created the polymer and Liu’s team made the material into a fiber.

Yang had already developed a citrate polymer for scaffolds for bone regeneration in his previous research. Now the team is using the material for both the core and cladding. “The use of the citrate-based polymers enables ultrafine tuning of refractive index differences between the core and the cladding layers,” Chenji Zhang, a Ph.D. graduate working on the project, explains in the release.

The citrate-based polymer enables the optical fiber to bend and stretch without separating, since the core and cladding are made of the same flexible material. And the other benefit of using a biodegradable material is that it doesn’t need to be removed. “Because the material is nontoxic and biodegradable, the citrate-based fiber could be left inside the body for long periods without the need for a second surgery to remove it,” Yang says. He adds that the optical fibers also can be used to deliver drugs or therapeutic chemicals to treat diseases.

“This new type of fiber creates a transparent window for peeking into a turbid tissue, and can enable new opportunities for imaging,” Liu adds.

The paper, published in Biomaterials, is “Flexible biodegradable citrate-based polymeric step-index optical fiber” (DOI: 10.1016/j.biomaterials.2017.08.003).

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