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The pathophysiological progress of Parkinson's disease leads through degeneration of dopaminergic neurons in the substantia nigra to complete cell death and lack of dopamine in the striatum where it modulates motor functions. Transplantation of dopaminergic stem cell-derived neurons is a possible therapy to restore dopamine levels. We have previously presented multifunctional pyrolytic carbon coated leaky optoelectrical fibers (LOEFs) with laser ablated micro-optical windows (µOWs) as carriers for channelrhodopsin-2 modified optogenetically active neurons for light-induced on-demand dopamine release and amperometric real-time detection. To increase the dopamine release by stimulating a larger neuronal population with light, we present here a novel approach to generate µOWs through laser ablation around the entire circumference of optical fibers to obtain Omni-LOEFs. Cyclic voltammetric characterization of the pyrolytic carbon showed that despite the increased number of µOWs, the electrochemical properties were not deteriorated. Finally, we demonstrate that the current recorded during real-time detection of dopamine upon light-induced stimulation of neurons differentiated on Omni-LOEFs is significantly higher compared to recordings from the same number of cells seeded on LOEFs with µOWs only on one side. Moreover, by varying the cell seeding density, we show that the recorded current is proportional to the dimension of the cell population.

Compartmentalized microfluidic platforms are an invaluable tool in neuroscience research. However, harnessing the full potential of this technology remains hindered by the lack of a simple fabrication approach for the creation of intricate device architectures with high-aspect ratio features. Here, a hybrid additive manufacturing approach is presented for the fabrication of open-well compartmentalized neural devices that provides larger freedom of device design, removes the need for manual postprocessing, and allows an increase in the biocompatibility of the system. Suitability of the method for multimaterial integration allows to tailor the device architecture for the long-term maintenance of healthy human stem-cell derived neurons and astrocytes, spanning at least 40 days. Leveraging fast-prototyping capabilities at both micro and macroscale, a proof-of-principle human in vitro model of the nigrostriatal pathway is created. By presenting a route for novel materials and unique architectures in microfluidic systems, the method provides new possibilities in biological research beyond neuroscience applications.

Compartmentalized microfluidic platforms are an invaluable tool in neuroscience research. However, harnessing the full potential of this technology remains hindered by the lack of a simple fabrication approach for the creation of intricate device architectures with high-aspect ratio features. Here, a hybrid additive manufacturing approach is presented for the fabrication of open-well compartmentalized neural devices that provides larger freedom of device design, removes the need for manual postprocessing, and allows an increase in the biocompatibility of the system. Suitability of the method for multimaterial integration allows to tailor the device architecture for the long-term maintenance of healthy human stem-cell derived neurons and astrocytes, spanning at least 40 days. Leveraging fast-prototyping capabilities at both micro and macroscale, a proof-of-principle human in vitro model of the nigrostriatal pathway is created. By presenting a route for novel materials and unique architectures in microfluidic systems, the method provides new possibilities in biological research beyond neuroscience applications.

This paper reports on the fabrication and characterization of leaky opto-electrical neural probes for optical stimulation and real time electrochemical detection of dopamine exocytosis from optogenetically modified neural stem cells. Indentations were introduced in a SU-8 waveguide structure, patterned directly on the probe shank, to allow light to leak over a large area. Pyrolytic carbon electrodes fabricated on both sides of the leaky waveguide allow for real time detection of dopamine. The electrochemical characterization of the pyrolytic carbon demonstrates excellent conductivity and suitability for dopamine detection.

Parkinson’s disease (PD) is characterized by the degeneration of dopaminergic neurons in the midbrain. The most effective therapy for the treatment of PD is administration of levodopa. However, it leads to the development of motor complications. Continuous delivery of dopamine has been shown to reduce the risks associated with chronic motor complications [1]. This work presents the fabrication and characterization of a microfabricated implantable leaky optical neural probe to fulfil three functions: i) it acts as a cell culture substrate for application in cell replacement therapy (CRT). ii) the leaky waveguide on the probe enables optical stimulation of neural stem cell derived optogenetic neurons differentiated on the probe. iii) pyrolytic carbon electrodes allow electrochemical detection of dopamine exocytosis and modulation of its continuous supply in the striatum for application in Parkinson’s disease (PD) therapy. The neural probes are optimized for a mouse brain (4 mm long, 50 µm thick and 200 µm wide). The width is necessary for differentiating a large number of stem cells for application in CRT. Electrodes with micropillars are patterned in SU-8 and pyrolysed to obtain the working (WE) and counter electrodes (CE) while gold is used as a pseudo reference electrode (RE) for electrochemical measurements. Pyrolytic carbon is used as cell substrate as it supports differentiation of neural stem cells into dopaminergic neurons [2]. ASU-8 waveguide was designed along the probe edge to encapsulate the cells during implantation and enable optogenetic stimulation of a large population of neurons in the immediate vicinity of the waveguide without the need to increase input optical power. The probes are fabricated using a combination of front and backside silicon etching. The backside etch defines the probe thickness while the front side etch releases the probe and defines the groove for the placement of an optical fiber for coupling light into the waveguide. F

In Parkinson's disease, the degeneration of dopaminergic neurons in substantia nigra leads to a decrease in the physiological levels of dopamine in striatum. The existing dopaminergic therapies effectively alleviate the symptoms, albeit they do not revert the disease progression and result in significant adverse effects. Transplanting dopaminergic neurons derived from stem cells could restore dopamine levels without additional motor complications. However, the transplanted cells disperse in vivo and it is not possible to stimulate them on demand to modulate dopamine release to prevent dyskinesia. In order to address these issues, this paper presents a multifunctional leaky optoelectrical fiber for potential neuromodulation and as a cell substrate for application in combined optogenetic stem cell therapy. Pyrolytic carbon coated optical fibers are laser ablated to pattern micro-optical windows to permit light leakage over a large area. The pyrolytic carbon acts as an excellent electrode for the electrochemical detection of dopamine. Human neural stem cells are genetically modified to express the light sensitive opsin channelrhodopsin-2 and are differentiated into dopaminergic neurons on the leaky optoelectrical fiber. Finally, light leaking from the micro-optical windows is used to stimulate the dopaminergic neurons resulting in the release of dopamine that is detected in real-time using chronoamperometry.