FORTH develops bioresorbable fiber Bragg gratings

13 Feb 2018

Optical fiber sensors that can be safely implanted into the body could assist diagnosis and treatment.

The ability to fabricate implantable optical components from materials which are subsequently destroyed by the human body and safely disappear has been an attractive concept for some time. But the combination of a bioresorbable nature and specific desired optical properties has been challenging to produce.

A team at Greece's Foundation for Research and Technology – Hellas (FORTH) has now fabricated fiber Bragg gratings (FBGs) inside optical fibers designed to dissolve completely within the body, potentially allowing them to be used for in-body monitoring of bone fracture healing, or monitoring of sensitive organs such as the brain.

In a study published in Optics Letters, researchers from FORTH, working with Italian researchers from Polytechnic University of Turin and Istituto Superiore Mario Boella, demonstrated what is said to be the first inscription of Bragg gratings in a bioresorbable phosphate glass optical fiber, and then monitored the fiber's dissolution in a solution whose pH and temperature resembled those of the human body.

"Our work paves the way toward optical fiber sensors that can be safely inserted into the human body," said FORTH's Maria Konstantaki. "Because they dissolve, these sensors don’t need to be removed after use, and would enable new ways to perform treatments and diagnoses in the body."

In the published paper, the team noted that although the inscription of Bragg gratings in phosphate and phosphosilicate glass optical fibers has been demonstrated in the past using deep ultraviolet laser radiation, the current goal was to investigate more precisely how Bragg gratings inscribed in bioresorbable optical fibers will behave under controlled dissolution conditions.

Changes in both the spectral behavior and physical morphology over the course of 56 hours immersion were monitored, revealing that modifications to the reflected signal started to become apparent after a few hours in the solution. Additional cladding mode peaks appeared initially, with more prolonged immersion leading to substantial modifications of the fundamental FBG peak.

Customized properties
The project employed a customized glass made of phosphorous oxide combined with oxides of calcium, magnesium, sodium and silicon, but it is likely that glasses of different composition will demonstrate different dissolution properties.

"It is expected that tuning the phosphate glass composition could lead to the fabrication of multi-cladding optical fibers of controlled dissolution, for which the fundamental mode is not largely affected by the wet etching of the fiber cladding during the time span required for a specific application," noted the team in the published paper.

The next steps in the project will involve experiments to better understand this aspect, and how both the fiber composition and the ultraviolet laser irradiation affect the speed at which the fiber Bragg grating dissolves. Animal trials could then follow.

Optimized bioresorbable FBGs could ultimately be used to sense pressure at joints in the body, or to safely reach and assess the heart or other delicate organs. Laser-based techniques for removing tumors might also be improved, as the fibers could simultaneously deliver the laser beam and provide the accurate real-time temperature sensing necessary to monitor the laser ablation process.

“This finding paves the way for new applications of these types of materials, particularly in the fiber form,” said Stavros Pissadakis, leader of the FORTH group. “Complex fluidic or optical structures could be created using lasers to make a device with a host of tailored functionalities.”