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Infrared neurostimulation has emerged in recent years as a promising technique for controlling neuronal activity without genetic manipulation. Having high absorption of the employed wavelengths as its fundamental mechanism, it requires implantable platforms to deliver light in brain regions deeper than the first cortical layers. Due to the spatial confinement of the stimulation, electrodes integrated in close proximity to the illumination spot are desirable to verify the effects of the stimulation by extracellular electrophysiology. Here we developed and validated in vivo a multifunctional neural interface based on a soft, biocompatible polymer optical fiber that allows simultaneous infrared neurostimulation and electrophysiology.

Implantable optical fibers have been widely used for optical neuromodulation in deep brain regions. Polymer fiber-based neural devices have natural advantages over silica fibers since their high flexibility would lead to a less inflammatory response in chronic in vivo experiments. Using three kinds of polymer materials: polycarbonate (PC), polysulfone (PSU), and fluorinated ethylene propylene (FEP), we present multifunctional soft polymer fiber (POF)-based brain implants with an ultra-high numerical aperture (UHNA) and integrated microfluidic channels (MCs) for wide illumination and drug delivery, respectively. The flexibility of the proposed fiber devices has been found to be 100-fold reduced compared to their commercially available counterparts. Biofluids delivery can be controllably achieved over a wide range of injection rates spanning from 10 nL/min to 1000 nL/min by the structured MCs in the fiber cladding. The illumination area of the UHNA POFs in brain phantom has been increased significantly compared with the commercially available silica fibers. A fluorescent light recording experiment has been conducted to demonstrate the proposed UHNA POFs can be used as optical waveguides in fiber photometry. The limited illumination angle of the optical fiber imposed by current technology has been enlarged by the proposed UHNA POFs and we anticipate our work to pave the way toward more efficient multifunctional neural probes for neuroscience.

Implantable optical fibers have been widely used for optical neuromodulation in deep brain regions. Polymer fiber-based neural devices have natural advantages over silica fibers since their high flexibility would lead to a less inflammatory response in chronic in vivo experiments. Using three kinds of polymer materials: polycarbonate (PC), polysulfone (PSU), and fluorinated ethylene propylene (FEP), we present multifunctional soft polymer fiber (POF)-based brain implants with an ultra-high numerical aperture (UHNA) and integrated microfluidic channels (MCs) for wide illumination and drug delivery, respectively. The flexibility of the proposed fiber devices has been found to be 100-fold reduced compared to their commercially available counterparts. Biofluids delivery can be controllably achieved over a wide range of injection rates spanning from 10 nL/min to 1000 nL/min by the structured MCs in the fiber cladding. The illumination area of the UHNA POFs in brain phantom has been increased significantly compared with the commercially available silica fibers. A fluorescent light recording experiment has been conducted to demonstrate the proposed UHNA POFs can be used as optical waveguides in fiber photometry. The limited illumination angle of the optical fiber imposed by current technology has been enlarged by the proposed UHNA POFs and we anticipate our work to pave the way toward more efficient multifunctional neural probes for neuroscience., Implantable optical fibers have been widely used for optical neuromodulation in deep brain regions. Polymer fiber-based neural devices have natural advantages over silica fibers since their high flexibility would lead to a less inflammatory response in chronic in vivo experiments. Using three kinds of polymer materials: polycarbonate (PC), polysulfone (PSU), and fluorinated ethylene propylene (FEP), we present multifunctional soft polymer fiber (POF)-based brain implants with an Ultra-High Numerical Aperture (UHNA) and integrated Microfluidic Channels (MCs) for wide illumination and drug delivery, respectively. The flexibility of the proposed fiber devices has been found to be 100-fold reduced compared to their commercially available counterparts. Biofluids delivery can be controllably achieved over a wide range of injection rates spanning from 10 nL/min to 1000 nL/min by the structured MCs in the fiber cladding. The illumination area of the UHNA POFs in brain phantom has been increased significantly compared with the commercially available silica fibers. A fluorescent light recording experiment has been conducted to demonstrate the proposed UHNA POFs can be used as optical waveguides in fiber photometry. The limited illumination angle of the optical fiber imposed by current technology has been enlarged by the proposed UHNA POFs and we anticipate our work to pave the way toward more efficient multifunctional neural probes for neuroscience.

Variation of the brain temperature is strongly affected by blood flow, oxygen supply, and neural cell metabolism. Localized monitoring of the brain temperature is one of the most effective ways to correlate brain functions and diseases such as stroke, epilepsy, and mood disorders. While polymer optical fibers (POFs) are considered ideal candidates for temperature sensing in the brain, they have never been used so far in vivo. Here, we developed for the first, to the best of our knowledge, time an implantable probe based on a microstructured polymer optical fiber Bragg grating (FBG) sensor for intracranial brain temperature mapping. The temperature at different depths of the brain (starting from the cerebral cortex) and the correlation between the brain and body core temperature of a rat were recorded with a sensitivity of 33 pm/°C and accuracy <0.2°C. Our in vivo experimental results suggest that the proposed device can achieve real-time and high-resolution local temperature measurement in the brain, as well as being integrated with existing neural interfaces., Variation of the brain temperature is strongly affected by blood flow, oxygen supply, and neural cell metabolism. Localized monitoring of the brain temperature is one of the most effective ways to correlate brain functions and diseases such as stroke, epilepsy, and mood disorders. While polymer optical fibers (POFs) are considered ideal candidates for temperature sensing in the brain, they have never been used so far in vivo. Here, we developed for the first, to the best of our knowledge, time an implantable probe based on a microstructured polymer optical fiber Bragg grating (FBG) sensor for intracranial brain temperature mapping. The temperature at different depths of the brain (starting from the cerebral cortex) and the correlation between the brain and body core temperature of a rat were recorded with a sensitivity of 33 pm/°C and accuracy <0.2°C. Our in vivo experimental results suggest that the proposed device can achieve real-time and high-resolution local temperature measurement in the brain, as well as being integrated with existing neural interfaces.

Due to their flexibility and robustness, polymer optical fibers represent a promising platform for the development of brain-compatible implantable devices with reduced risk of tissue inflammation. Furthermore, by combining different biocompatible materials it is possible to integrate multiple functionalities in a single hybrid optical fiber. This approach allows the fabrication of soft brain interfaces able to support multiple modalities of neural interrogation. Such interfaces capable of simultaneous light delivery and recording of neuronal activity with minimal tissue damage are currently lacking for infrared wavelengths in the strong water absorption region. This spectral region, in particular, is crucial for infrared neuromodulation, a promising technique for direct light-induced control of neural activity without genetic manipulation. Here we present novel infrared fiber-based neural interfaces developed by thermal drawing of soft, biocompatible optical polymers, which are able to simultaneously modulate and record neural activity, as validated experimentally in vivo.

Objective: Optical fiber devices constitute significant tools for the modulation and interrogation of neuronal circuitry in the mid and deep brain regions. The illuminated brain area during neuromodulation has a direct impact on the spatio-temporal properties of the brain activity and depends solely on the material and geometrical characteristics of the optical fibers. In the present work, we developed two different flexible polymer optical fibers (POFs) with integrated microfluidic channels (MFCs) and an ultra-high numerical aperture (UHNA) for enlarging the illumination angle to achieve efficient neuromodulation. Approach: Three distinct thermoplastic polymers: polysulfone (PSU), polycarbonate (PC), and fluorinated ethylene propylene (FEP) were used to fabricate two step-index UHNA POF neural devices using a scalable thermal drawing process. The POFs were characterized in terms of their illumination map as well as their fluid delivery capability in phantom and adult rat brain slices. Main results: A 100-fold reduced bending stiffness of the proposed fiber devices compared to their commercially available counterparts has been found. The integrated MFCs can controllably deliver dye (trypan blue) on-demand over a wide range of injection rates spanning from 10 nL/min to 1000 nL/min. Compared with commercial silica fibers, the proposed UHNA POFs exhibited an increased illumination area by 17% and 21% under 470 and 650 nm wavelength, respectively. In addition, a fluorescent light recording experiment has been conducted to demonstrate the ability of our UHNA POFs to be used as optical waveguides in fiber photometry. Significance: Our results overcome the current technological limitations of fiber implants that have limited illumination area and we suggest that soft neural fiber devices can be developed using different custom designs for illumination, collection, and photometry applications. We anticipate our work to pave the way towards the dev

In this work we present a novel optrode fabricated by thermal drawing to perform simultaneous infrared neuromodulation and electrophysiological recording. The device has been tested in vivo, showing to be suitable for the intended application.

We present here a new soft polymer fiber-based neural device with an ultra-high numerical aperture (UHNA) and integrated microfluidic channels (MFC) for neuromodulation.

Fabrication of graded index (GRIN) fibers was for a long time limited to ion‐exchange, modified chemical vapour deposition (MCVD) or other deposition techniques. Recently, the nanostructuring of an all‐solid core in fibers has proven to be a versatile and low cost alternative for the production of gradient index optical fibers. In this work, high purity chalcogenide glasses in the Ge‐As‐Se glass system, synthesized in‐house, were used for stacking and drawing chalcogenide nanostructured GRIN fibers designed using the Maxwell‐Garnett effective medium theory, simulated annealing and genetic algorithms. The successful generation of a supercontinuum spanning the mid‐infrared from 3 µm to 6 µm, pumping at a central wavelength of 4 µm using an Optical Parametric Oscillator with femtoseconds pulses, is also reported.