Patch-clamping mit Mikroöffnungen in Polyimide-Folien

Die Patchclamp-Technik ist die aussagekräftigste Methode zur Untersuchung der Funktion und Regulation von Ionenkanälen. Sie basiert auf der Bildung eines engen Kontaktes zwischen der Spitze einer Glasspipette und der Membran einer Zelle, an die die Pipette herangeführt wird. Aus dem engen Kontakt resultiert ein elektrischer Widerstand im Gigaohm-Bereich zwischen der Elektrolytlösung im Innern der Pipette und der die Zelle und Pipette umgebenden Elektrolytlösung. Trotz der weitverbreiteten Verwendung dieser Methode ist die wahre Natur dieses Kontaktes und der resultierenden hochohmigen „Seal“-Bildung noch immer nicht im Detail verstanden. Zudem ist die Patchclamp-Methode zeitaufwendig und erfordert erfahrene Anwender sowie gutausgerüstete Setups. Im Moment ist noch keine Vorrichtung beschrieben, die diesen “Cell-by-cell”-Assay vollautomatisch durchführt. Dies ist jedoch die Voraussetzung für Automatisierung, Miniaturisierung und Parallelisierung, um mit dieser Methode Hochdurchsatz-Untersuchungen von pharmazeutischen Substanzen durchführen zu können. Mehrere Gruppen berichten über einen Ansatz, der die Glasspipette durch eine mikromechanisch gefertigte Siliziumstruktur ersetzen soll. Sie verwenden ein dünnes Diaphragma, in das ein mikroskopisch kleines Loch (Durchmesser im Nano- und Mikrometer-Bereich) eingebracht ist. Darauf werden Lipidvesikel aufgebracht, die per Adhäsion die Umgebung der Mikroöffnung hochohmig abdichten. Mit dieser Methode lassen sich Einzelkanalströme messen

PEDOT–CNT Composite Microelectrodes for Recording and Electrostimulation Applications: Fabrication, Morphology, and Electrical Properties

Composites of carbon nanotubes and poly(3,4-ethylenedioxythiophene, PEDOT) and layers of PEDOT are deposited onto microelectrodes by electropolymerization of ethylenedioxythiophene in the presence of a suspension of carbon nanotubes and polystyrene sulfonate. Analysis by FIB and SEM demonstrates that CNT–PEDOT composites exhibit a porous morphology whereas PEDOT layers are more compact. Accordingly, capacitance and charge injection capacity of the composite material exceed those of pure PEDOT layers. In vitro cell culture experiments reveal excellent biocompatibility and adhesion of both PEDOT and PEDOT–CNT electrodes. Signals recorded from heart muscle cells demonstrate the high S/N ratio achievable with these electrodes. Long-term pulsing experiments confirm stability of charge injection capacity. In conclusion, a robust fabrication procedure for composite PEDOT–CNT electrodes is demonstrated and results show that these electrodes are well suited for stimulation and recording in cardiac and neurophysiological research

Subretinal electronic chips allow blind patients to read letters and combine them to words

A light-sensitive, externally powered microchip was surgically implanted subretinally near the macular region of volunteers blind from hereditary retinal dystrophy. The implant contains an array of 1500 active microphotodiodes (‘chip’), each with its own amplifier and local stimulation electrode. At the implant's tip, another array of 16 wire-connected electrodes allows light-independent direct stimulation and testing of the neuron–electrode interface. Visual scenes are projected naturally through the eye's lens onto the chip under the transparent retina. The chip generates a corresponding pattern of 38 × 40 pixels, each releasing light-intensity-dependent electric stimulation pulses. Subsequently, three previously blind persons could locate bright objects on a dark table, two of whom could discern grating patterns. One of these patients was able to correctly describe and name objects like a fork or knife on a table, geometric patterns, different kinds of fruit and discern shades of grey with only 15 per cent contrast. Without a training period, the regained visual functions enabled him to localize and approach persons in a room freely and to read large letters as complete words after several years of blindness. These results demonstrate for the first time that subretinal micro-electrode arrays with 1500 photodiodes can create detailed meaningful visual perception in previously blind individuals

Chemical stimulation of adherent cells by localized application of acetylcholine from a microfluidic system

Chemical stimulation of cells is inherently cell type selective in contrast to electro-stimulation. The availability of a system for localized application of minute amounts of chemical stimulants could be useful for dose related response studies to test new compounds. It could also bring forward the development of a novel type of neuroprostheses.In an experimental setup micro-droplets of an acetylcholine solution were ejected from a fluidic microsystem and applied to the bottom of a nanoporous membrane. The solution travelled through the pores to the top of the membrane on which TE671 cells were cultivated. Calcium imaging was used to visualize cellular response with temporal and spatial resolution. Experimental demonstration of chemical stimulation for both threshold gated stimulation as well as accumulated dose response was achieved by either employing acetylcholine as chemical stimulant or applying calcein uptake, respectively.Numerical modelling and simulation of transport mechanisms involved were employed to gain a theoretical understanding of the influence of pore size, concentration of stimulant and droplet volume on the spatial-temporal distribution of stimulant and on the cellular response. Diffusion, pressure driven flow and evaporation effects were taken into account. Fast stimulation kinetic is achieved with pores of 0.82 µm diameter, whereas sustained substance delivery is obtained with nanoporous membranes. In all cases threshold concentrations ranging from 0.01 to 0.015 µM acetylcholine independent of pore size were determined

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

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

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

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%