Interfacing electrogenic cells on carbon materials

This thesis aims to illuminate two different approaches to improve electrical implants in the future. The approaches aim to reduce the formation of glia scars and improve the life time of the implanted electrodes. The first approach is to further improve materials that are already used as electrode material. The second approach is to use less invasive and more flexible substrates. In general, the focus of this thesis is on carbon materials. Commonly used, as well as new materials, are covered in this thesis. New materials feature great properties, for example good conductance, being inert and stable. Nevertheless, for being used first in cell culture and in the future in tissue, their biocompability with cells has to be tested. Therefore, a deeper understanding of the interface between cells and different substrates is of interest. The investigation of the attachment gives not only information about the growth of the cells, but also about the minimum surface the cells require to attach. Electrogenic cells are used to mimic the electric active organs in our body, the heart and the brain. For this purpose the cardiomyocyte cell line HL-1 and primary cortical neuronal cells were used. As one promising candidate, graphene was used. The biocompability of neuronal and HL-1 cells was tested successfully. Graphene was processed in two different devices: Multielectrode arrays (MEAs) and field-effect transistors (FETs). With both devices it was possible to record cell signals with a signal-to-noise-ratio (SNR) of up to 10. Additionally, neuronal cells were patched on a graphene MEA (GMEA) to measure intracellular signals. The cells were simultaneously measured with the patch pipette and with the GMEA device. For observations of cell growth on the device, cells growing on top of an electrode opening were cut using a focused ion beam (FIB). Thus, a close adhesion from cell to substrate could be proven. On the one hand, protein patterns were printed using microcontact printing on top of devices. On the other hand graphene was patterned in stripes to guide the neurites. Thus, it was possible to achieve a guidance of neuronal growth.Furthermore, new designs for electrodes were tested, such as 3D nanostructures to get as close as possible to the cell. Here, diamond covered carbon nanotubes (DCNT) and graphene foam were successfully tested for their biocompability with HL-1 and neuronal cells. Additionally, the attachment and cell adhesion were investigated. The minimum attachment of cells to 3D nanostructures is around 25%. Both materials could be possible candidates for future electrode materials. The second approach uses more flexible substrates to provide a softer ground for the cell. First, a protocol was established to grow cells on hydrophobic polymer substrates and a staining procedure to view polymer samples under a scanning electron microscope (SEM) and cut them with a FIB. Thus, it was possible to examine the attachment of the cells to the substrates. Afterwards, flexible devices were produced using inkjet printing. With electrodes made of printed carbon ink, cellular signals of HL-1 cells were measured.In summary it can be said that two different approaches for validating electrodes were successfully tested. This work functions as a foundation for further experiments