Flexible, diamond-based microelectrodes fabricated using the diamond growth side for neural sensing.

Diamond possesses many favorable properties for biochemical sensors, including biocompatibility, chemical inertness, resistance to biofouling, an extremely wide potential window, and low double-layer capacitance. The hardness of diamond, however, has hindered its applications in neural implants due to the mechanical property mismatch between diamond and soft nervous tissues. Here, we present a flexible, diamond-based microelectrode probe consisting of multichannel boron-doped polycrystalline diamond (BDD) microelectrodes on a soft Parylene C substrate. We developed and optimized a wafer-scale fabrication approach that allows the use of the growth side of the BDD thin film as the sensing surface. Compared to the nucleation surface, the BDD growth side exhibited a rougher morphology, a higher sp 3 content, a wider water potential window, and a lower background current. The dopamine (DA) sensing capability of the BDD growth surface electrodes was validated in a 1.0 mM DA solution, which shows better sensitivity and stability than the BDD nucleation surface electrodes. The results of these comparative studies suggest that using the BDD growth surface for making implantable microelectrodes has significant advantages in terms of the sensitivity, selectivity, and stability of a neural implant. Furthermore, we validated the functionality of the BDD growth side electrodes for neural recordings both in vitro and in vivo. The biocompatibility of the microcrystalline diamond film was also assessed in vitro using rat cortical neuron cultures.

Differentiation and characterization of neurons derived from rat iPSCs.

BACKGROUND: Induced pluripotent stem cells (iPSCs) may be an advantageous source of neuronal cells to repair damage due to neurological disorders or trauma. Additionally, they are promising candidates to develop models to study underlying mechanisms of neurodegenerative diseases. While successful neural differentiation of iPSCs has been reported in mice, protocols detailing the generation of neural cells from rat iPSCs are relatively limited, and their optimization by manipulating cell culture methods has remained unexplored. NEW METHOD: Here, we describe and compare the effects of four distinct, commonly used substrates on the neuronal differentiation of rat iPSC (riPSC) derived-neural progenitor cells. Our approach is to use substrate coating as a method to enrich differentiated riPSCs for neuronal subtypes with the desired morphology and maturity. We use a combination of electrophysiology, immunofluorescence staining, and Sholl analysis to characterize the cells generated on each substrate over a nine-day time course. RESULTS: The surface coating presented by the cell culture substrate influences the polarity and arborization of differentiating neurons. Polyornithine-laminin coating promoted neuronal arborization and maturation, while Geltrex favored bipolar cells which displayed indicators of functional immaturity. Poly-d-lysine substrate was associated with limited neurite outgrowth and arborization. Gelatin was the least favorable substrate for the growth and differentiation of our cells. Comparison with Existing Method: Rat-derived neural progenitor cells have been previously derived; however, our methods to use substrate coatings to influence morphological and electrical maturity have not been explored previously. CONCLUSION: Substrate coatings can be selected to enrich differentiated riPSCs for distinctive neuronal morphologies.