The polymer optical fiber in action. Credit: Chenji Zhang, Dingying Shan, Penn State.
The polymer optical fiber in action. Credit: Chenji Zhang, Dingying Shan, Penn State.

Shining a light on disease deep inside the body could become more convenient using pioneering optical fibres created at Pennsylvania State University (Penn State), USA. “We have developed a fully biodegradable, elastic and implantable polymer fibre,” explains Jian Yang. Yang and his colleagues report their innovation in a paper published in Biomaterials.

Fine optical fibres made of silica glass are currently used to collect images for diagnosing disease and monitoring the progress of treatment. Researchers and clinicians are also exploring the potential for using the light energy they deliver to stimulate the release of drugs at specific target sites. These existing fibres, however, come with problems and limitations. “Traditional silica glass fibres are brittle, fragile and not degradable,” says Zhiwen Liu, a co-author of the paper. These silica glass fibres can also provoke adverse inflammatory and toxic reactions due to poor biocompatibility.

In comparison, the fibres created by Yang and his colleagues could sit within living tissue for as long as required without any biocompatibility problems. They are flexible, efficient at transmitting light, and will harmlessly biodegrade when their task is complete. The length of time taken to biodegrade can be easily manipulated, from a few weeks to over a year, by a simple adjustment of the chemical structure. Yang believes that these advantages over traditional optical fibres will make diagnosis and light-based therapy easier and more effective with fewer complications, while achieving the same basic functions as existing fibres.

If, for example, a patient has a deep-seated tumor, leaving a biocompatible optical fibre in place during treatment could allow the treatment’s effectiveness to be monitored as it is being implemented. There would be no need for the repeated removal and insertion that is sometimes currently required to prevent adhesion to surrounding tissues and other incompatibility problems.

The new biodegradable polymer is built from molecules of citric acid and maleic acid, both of which either can be found in fruit and vegetables or are considered biocompatible. These components are then linked up to create the flexible polymer that efficiently transmits light.

Other research groups have developed similar polymer fibres, but the Penn State team has incorporated a crucial new feature using new materials. "We create a light-transmitting core surrounded by an outer cladding," explains Yang. The core and the cladding are made of the same type of citrate polymers, but with significant differences in their interaction with light. In technical terms, the refractive index differs between the regions. This keeps the transmitted light within the core and moving efficiently along it.

“We hope to see our new optical fiber technology being used in clinical settings soon,” says Yang.

This article is based on research conducted by Yang, J. et al.: “Flexible biodegradable citrate-based polymeric optical fiber,” Biomaterials (2017).