Volker Bucher

Electrical properties of a light-addressable microelectrode chip with high electrode density for extracellular stimulation and recording of excitable cells

A light-addressable microelectrode chip with 3600 TiN electrodes was fabricated. Amorphous silicon (a-Si:H) serves as a photo conductor. The electrodes on the chip are addressed by a laser spot and electrical properties of the system are determined. DC measurements show a dark to bright dynamic of 10(6)-10(7). The AC impedance dynamic @ 1 kHz/100 mV and thus the signal-to-noise-ratio is determined to 60. This value is quite sufficient for electrophysiological measurements. For the first time, recordings from cardiac myocytes are reported using the principle of light-addressing. Measurements were done with a standard laser scan microscope (Zeiss LSM 410).

Low-impedance thin-film polycrystalline silicon microelectrodes for extracellular stimulation and recording

Abstract Polycrystalline silicon thin films were explored with respect to their application as low-impedance microelectrodes for extracellular stimulation and recording of cells. Microelectrode arrays (MEAs) comprising polysilicon microelectrodes were fabricated using CMOS-compatible processes. Overall capacitance of an electrode with a diameter of 20 μm is on the order of 200–300 pF. Chemical and morphological stability in physiological saline solution was excellent over a period of at least 5 months. This finding renders applications in neuronal implants or bio-chips. Nanoporous polysilicon electrodes were created by anodic oxidation in hydrofluoric acid (HF). However, no considerable decrease of electrode impedance was observed although pore formation was clearly confirmed by transmission electron microscopy (TEM).

Light-addressed sub-μm electrodes for extracellular recording and stimulation of excitable cells

Abstract An array of light-addressable sub-μm electrodes for contacting excitable cells is fabricated. These electrodes provide a free selectable cell–electrode contact with a high signal-to-noise ratio and high spatial resolution. A great number of lateral isolated sub-μm electrodes is placed on top of a photoconductor layer: hydrogenated amorphous silicon (a-Si:H). By use of a laser beam these sub-μm electrodes located under the cell can be selected forming an electrical contact via an indium tin oxide (ITO) lead to an amplifier, thus providing a high seal resistance at the cell–electrodes interface. The feasibility of light-addressing electrodes and fabrication of sub-μm electrodes on photoconductor layer is shown.

Electrical properties of light-addressed sub-μm electrodes fabricated by use of nanostencil-technology

A wide range of applications in neurotechnological research rely on planar microelectrode arrays (MEA) but the disadvantage of these systems is the low density of electrodes caused by the problem of wiring a great number of electrodes. In turn this results in a low number of good cell to electrode contacts. To overcome this drawback, a great number of laterally isolated sub-μm electrodes is placed on a photoconductor layer (amorphous silicon a-Si:H). By use of a laser beam, only those sub-μm electrodes lying under the cell can be selected to form an electrical contact to one of the underlying indium tin oxide (ITO) leads providing a high seal resistance at the cell/electrodes interface. A biocompatible and biostable composite layer of electrodes (100–500 nm) and insulator is formed using nanostencil-technology. Dark to bright ratio D of the photoconductor is determined to 105–106. The impedance of Au and TiN sub-μm electrodes in physiological solution is measured. Spatial resolution of the system is limited by light-scattering inside the supporting glass substrate; the effective diameter of the conductive region illuminated by the laser spot with intrinsic diameter 1.6 μm is ~6–7 μm.

Evaluation of adhesion promoters for Parylene C on gold metallization

Abstract Delamination of thin film polymeric coatings from metallization layers is a common cause of failure in biomedical implants. To address the problem, different adhesion promotion techniques can be applied which include surface pre-treatment with oxygen and argon plasma and the use of different adhesion promoters. In this paper the applicability of titanium (Ti), silicon oxide (SiOx), diamond-like carbon (DLC), tetramethylsilane (TMS) and aluminium oxide (AlOx) as adhesion promoters is evaluated. A cross cut, peel and scratch test are used to qualify and quantify the adhesion before and after storage in phosphate buffered saline (PBS) for 48 hours at a temperature of 37 °C. Promising results could be achieved by a combination of Ti and DLC as well as by AlOx.

A demonstrator for a flexible active microelectrode array with high electrode number

Abstract The integration of dies is a possibility to reduce the number of conducting tracks within electrical active implants. For passive microelectrode arrays the number of conducting tracks limits the number of electrodes. By embedding an array of small dies (250 μm edge length) employed to amplify and multiplex the signals of 25 electrodes each into a flexible foil we create a flexible active microelectrode array with more than 1000 electrodes. A fabrication process was developed containing a transfer process for the dies as well as an embedding procedure. Here a non-functional Dummy-System is presented as a demonstrator proving the feasibility of the proposed microelectrode array.

Examination of dielectric strength of thin Parylene C films under various conditions

Abstract The breakdown voltage of the biocompatible polymer Parylene C was determined after storage in 60°C saline solution and treatment by autoclave. It occurred that both, storage at 60°C in saline solution and autoclaving, lead to distinct decrease of dielectric strength by approximately 50%.

Plasma treatment on novel carbon fiber reinforced PEEK cages to enhance bioactivity

Abstract Carbon fiber reinforced polyetheretherketone (CFR-PEEK) has similar mechanical properties to human bone and is considered as the best alternative material to substitute titanium for spine cage implants. To compensate its poor osteogenic properties and limited bioinertness, CFR-PEEK was coated with a thin film of titanium. In the study, we investigated the biological response in vitro of titanium coated CFR-PEEK with different vacuum plasma pretreatments. The so modified surface revealed first hints for a good cell response by excellent cell adhesion and morphology of human osteoblast – like cells MG 63 (ATXX:’CRL-1427). Thus, the findings show that surface roughness of CFR-PEEK material has a profound effect on the biological activity via vacuum plasma treatment.