Implantable and Biodegradable Poly(l‐lactic acid) Fibers for Optical Neural Interfaces

Abstract

represent inferior compatibility with biological systems (especially soft brain tissues) due to their high stiffness and long-time stability, which lead to deleterious effects like tissue damage, inflammation, and rejection. [4] Flexible and stretchable polymeric fibers with designed microstructures are explored for neurological studies, enabling integrated electrical sensing, optical stimulation, and controlled microfluidic delivery. [5] In medical practice, biodegradable organic and inorganic materials including metals, semiconductors, and polymers have been exploited to form biological structures (drugs, stents, scaffolds, etc.) [6] and functional devices (electrical, optical, mechanical, and thermal sensors). [7] In comparison to devices and systems made of inert materials, these biodegradable implants that can physically disappear in biological tissues to eliminate the risk associated with further retraction or removal, providing enormous potential to biomedical applications and particularly clinical uses. Recently, waveguides and photonic structures based on biodegradable materials like ceramics (e.g., calcium phosphates), [8] synthetic polymers, [9] hydrogels, [10] and even bioderived materials (e.g., silks) [11] are investigated in both in vitro and in vivo studies. So far, these biodegradable photonic materials and structures have not been utilized as implantable fibers to study deep-brain neural activities. Here, we present poly(l-lactic acid) (PLLA)-based optical fibers as a biodegradable Advanced optical fibers and photonic structures play important roles in neuroscience research, along with recent progresses of genetically encoded optical actuators and indicators. Most techniques for optical neural implants rely on fused silica or long-lasting polymeric fiber structures. In this paper, implantable and biodegradable optical fibers based on poly(l-lactic acid) (PLLA) are presented. PLLA fibers with dimensions similar to standard silica fibers are constructed using a simple thermal drawing process at around 220 °C. The formed PLLA fibers exhibit high mechanical flexibility and optical transparency, and their structural evolution and optical property changes are systematically studied during in vitro degradation. In addition, their biocompatibility with brain tissues is evaluated in living mice, and full in vivo degradation is demonstrated. Finally, PLLA fibers are implemented as a tool for intracranial light delivery and detection, realizing deep brain fluorescence sensing and optogenetic interrogation in vivo. The presented materials and device platform offer paths to fully biocompatible and bioresorbable photonic systems for biomedical uses. Biodegradable Fibers

Bioresorbable Materials on the Rise: From Electronic Components and Physical Sensors to In Vivo Monitoring Systems

“…In 2018, Fu et al reported PLLA optical fibers to be used as a bioresorbable optical neural interconnection between biological matter and optical instrumentation, thanks to negligible optical losses and high transmission coefficient (about 95%) of amorphous PLLA in the visible range . The fiber diameter was tuned to about 220 µm, like that of standard silica optical fibers, to facilitate interconnection with commercial optical components.…”

Recent Advances in Biointegrated Optoelectronic Devices

“…Under these circumstances, biointegrated electronic and optical devices that dissolve naturally in physiological conditions have received much attention since potential risk of surgical complications can be avoided. Comprising solely of biodegradable active materials (metals, semiconductors, and dielectrics) and encapsulants, implantable optoelectronic devices consisted of photonic crystals, photodetectors, solar cells, waveguides, and light emitters can dissolve in biological environments in a controlled manner after use (Figure f).…”

“…One of the established tools for intracranial light delivery and detection is by use of implantable optical fibers (and waveguides in most cases) for deep brain optogenetic stimulation and fluorescence detection in vivo . As to the optical neural interface, standard silica glass, fibers, and waveguides based on flexible, stretchable and even biodegradable materials have been thoroughly explored . Recently, developed multifunctional fibers incorporate electrodes and microchannels in the microstructure to enable simultaneous optical stimulation, electrophysiological sensing, and drug delivery …”

Biological Considerations of Optical Interfaces for Neuromodulation

“…Microdrive interfaces have been developed using screws and guide tubes, or via electrically induced thermal expansion . For shorter term implants, biodegradable devices have been proposed to reduce the chronic response, such as flexible optical fibers from poly( l ‐lactic acid) with dimensions similar to standard silica fibers . Intracranial light delivery and detection has been demonstratedin vivo in mice, followed by full degradation …”