In vivo evaluation of thermally drawn biodegradable optical fibers as brain neural interfaces

Optical fiber technology has a critical role in modern neuroscience towards understanding the complex neuronal dynamics within the nervous system. In this study, we manufactured amorphous thermally drawn poly D, L-lactic acid (PDLLA) optical fibers in different diameters. These fibers were then implanted into the lateral posterior (LP) region of the mouse brain for 4 months, allowing us to assess their degradation characteristics. The gradual dissolution of the implanted PDLLA optical fibers in the brain was confirmed by optical microscope and scanning electron microscopy (SEM), molecular weight measurements, and light transmission spectroscopy. The results indicate that the degradation rate was mainly pronounced during the first week. Degradation after 4 months resulted in the formation of micropores on the surface of the implanted fiber within the gray matter region of the brain. Moreover, the current PDLLA optical fiber implant offers efficient light transmission in the short-wavelength near-infrared (SW-NIR) range. SW-NIR enables deeper tissue penetration and reduced light scattering, making it ideal for optogenetics and functional imaging with therapeutic potential in neurological disorders. We believe that the provided PDLLA optical fiber in this study constitutes a promising candidate for the development of next-generation biocompatible, soft, and biodegradable bi-directional neural interfaces