Biodegradable and biocompatible polymer optical fibers - "BIOPOFS": from fabrication to early proof-of-principle applications

Student thesis: Doctoral Thesis

Abstract

Light based-therapies can be applied to treat a variety of medical conditions, such as for promoting tissue regeneration during wound healing or for destructing cancer cells in a targeted manner and without harming surrounding tissue. However, the penetration of light from the outside into biological tissue is limited to a maximum depth of about 3 mm due to absorption and scattering by said tissue. Instead we should consider delivering light inside the tissue and directing it immediately to the desired location within the human body by ways of novel implantable light-guiding devices, such as dedicated optical fibers.

Optical fibers are commonly used for telecommunication purposes. They have also already found applications in medicine, such as for example in optical fiber-based endoscopes that allow imaging specific areas within the body. Standard optical fibers, however, are made of silica glass, and are thus not biocompatible, i.e. they can produce a toxic or immunological response when they are in contact with tissue or body fluids, which is a significant hindrance for many biomedical applications. Furthermore, glass shatters when it breaks, and sharp edges and debris could injure surrounding tissue.
The remaining debris would not disappear and would require surgical removal. In this respect, natural or synthetic polymer-based biomaterials may offer an interesting alternative to glass. Therefore, Polymer Optical Fibers (POFs) manufactured from biocompatible and biodegradable materials could offer a straightforward approach for deep-tissue light delivery and may allow for minimally invasive surgical implantation. Moreover, bioresorbable POFs could be left inside the body after having fulfilled their mission: they would degrade over time and be eliminated via the body’s natural pathways. In this dissertation, we therefore investigate such biocompatible and biodegradable polymer optical fibers, to which we refer as bioPOFs.

After a comparison of biodegradable and biocompatible polymers in terms of their suitability for polymer optical fiber production, we have selected well-known FDAregulated biocompatible amorphous polyesters, i.e. poly(D,L-lactic acid) – PDLLA and poly(D,L-lactic-co-glycolic acid) – PDLGA, which have already been exploited for the fabrication of various biomedical devices. Next, we have designed and manufactured
preforms of bioPOFs from these selected biomaterials that can be thermally drawn into bioPOFs using standard heat-draw towers. We then successfully fabricated unclad bioPOF, step-index bioPOF, and microstructured bioPOF in a repeatable manner and optically and chemically characterized these new optical fibers. We achieved record low optical loss values for these bioPOFs and we found that their operational lifetime meets the typical duration required by light-based therapy scenarios.

Finally we have also investigated early proof-of-concepts for potential applications of our bioPOFs. First, we used unclad bioPOF as a lightguide in a photodynamic therapy scenario for in vitro singlet oxygen generation, which is an active agent capable of destroying tumorous tissue. Second, we looked into a bioPOF-based biosensor consisting of a molecular sandwich-functionalized unclad PDLLA fiber for antigenantibody- based detection of a specific target: C-reactive protein, which is a well-known biomarker that indicates the occurrence of inflammatory processes and reveals the status of wound healing.

With the above we are convinced that we have indicated the great application potential of our bioPOFs. By doing so, we hope to have contributed to the development of a new class of optical fibers that can be actually implanted inside human bodies and enable advanced light-based therapies.
Date of Award30 Jun 2021
Original languageEnglish

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