Neuronal and glial cell co-culture organization and impedance spectroscopy on nanocolumnar TiN films for lab-on-a-chip devices.

Lab-on-a-chip devices, such as multielectrode arrays (MEAs), offer great advantages to study function and behavior of biological cells, such as neurons, outside the complex tissue structure. Nevertheless, in vitro systems can only succeed if they represent realistic conditions such as cell organization as similarly found in tissues. In our study, we employ a co-culture system of neuron-like (SH-SY5Y) and glial-like (U-87 MG) cells with various neuron-glial ratios to model different brain regions with different cellular compositions in vitro. We find that cell behavior in terms of cellular organization, as well as proliferation, depends on neuron-glial cell ratio, as well as the underlying substrate material. In fact, nanocolumnar titanium nitride (TiN nano), which exhibits improved electric properties for neural recording on MEA, shows improved biocompatible features compared to indium tin oxide (ITO). Moreover, electrochemical impedance spectroscopy experiments allow us to monitor cellular processes label-free in real-time over several days with multielectrode arrays. Additionally, electrochemical impedance experiments reveal superiority of TiN with nanocolumnar surface modification in comparison with ITO. TiN nano exhibits enhanced relative cell signals and improved signal-to-noise ratio, especially for smaller electrode sizes, which makes nanocolumnar TiN a promising candidate for research on neural recording and stimulation.

Adhesion of Neurons and Glial Cells with Nanocolumnar TiN Films for Brain-Machine Interfaces.

Coupling of cells to biomaterials is a prerequisite for most biomedical applications; e.g., neuroelectrodes can only stimulate brain tissue in vivo if the electric signal is transferred to neurons attached to the electrodes' surface. Besides, cell survival in vitro also depends on the interaction of cells with the underlying substrate materials; in vitro assays such as multielectrode arrays determine cellular behavior by electrical coupling to the adherent cells. In our study, we investigated the interaction of neurons and glial cells with different electrode materials such as TiN and nanocolumnar TiN surfaces in contrast to gold and ITO substrates. Employing single-cell force spectroscopy, we quantified short-term interaction forces between neuron-like cells (SH-SY5Y cells) and glial cells (U-87 MG cells) for the different materials and contact times. Additionally, results were compared to the spreading dynamics of cells for different culture times as a function of the underlying substrate. The adhesion behavior of glial cells was almost independent of the biomaterial and the maximum growth areas were already seen after one day; however, adhesion dynamics of neurons relied on culture material and time. Neurons spread much better on TiN and nanocolumnar TiN and also formed more neurites after three days in culture. Our designed nanocolumnar TiN offers the possibility for building miniaturized microelectrode arrays for impedance spectroscopy without losing detection sensitivity due to a lowered self-impedance of the electrode. Hence, our results show that this biomaterial promotes adhesion and spreading of neurons and glial cells, which are important for many biomedical applications in vitro and in vivo.

Proliferation and Cluster Analysis of Neurons and Glial Cell Organization on Nanocolumnar TiN Sub-Strates.

Biomaterials employed for neural stimulation, as well as brain/machine interfaces, offer great perspectives to combat neurodegenerative diseases, while application of lab-on-a-chip devices such as multielectrode arrays is a promising alternative to assess neural function in vitro. For bioelectronic monitoring, nanostructured microelectrodes are required, which exhibit an increased surface area where the detection sensitivity is not reduced by the self-impedance of the electrode. In our study, we investigated the interaction of neurons (SH-SY5Y) and glial cells (U-87 MG) with nanocolumnar titanium nitride (TiN) electrode materials in comparison to TiN with larger surface grains, gold, and indium tin oxide (ITO) substrates. Glial cells showed an enhanced proliferation on TiN materials; however, these cells spread evenly distributed over all the substrate surfaces. By contrast, neurons proliferated fastest on nanocolumnar TiN and formed large cell agglomerations. We implemented a radial autocorrelation function of cellular positions combined with various clustering algorithms. These combined analyses allowed us to quantify the largest cluster on nanocolumnar TiN; however, on ITO and gold, neurons spread more homogeneously across the substrates. As SH-SY5Y cells tend to grow in clusters under physiologic conditions, our study proves nanocolumnar TiN as a potential bioactive material candidate for the application of microelectrodes in contact with neurons. To this end, the employed K-means clustering algorithm together with radial autocorrelation analysis is a valuable tool to quantify cell-surface interaction and cell organization to evaluate biomaterials' performance in vitro.