Blaž Karpe

Electrochemical and Electrophysiological Performance of Platinum Electrodes Within the Ninety‐Nine‐Electrode Stimulating Nerve Cuff

The trend in neural prostheses using selective nerve stimulation for electrical stimulation therapies is headed toward single-part systems having a large number of working electrodes (WEs), each of which selectively stimulate neural tissue or record neural response (NR). The present article reviews the electrochemical and electrophysiological performance of platinum WE within a ninety-nine-electrode spiral cuff for selective nerve stimulation and recording of peripheral nerves, with a focus on the vagus nerve (VN). The electrochemical properties of the WE were studied in vitro using the electrochemical impedance spectroscopy (EIS) technique. The equivalent circuit model (ECM) of the interface between the WE and neural tissue was extracted from the EIS data and simulated in the time domain using a preset current stimulus. Electrophysiological performance of in-space and fiber-type highly selective vagus nerve stimulation (VNS) was tested using an isolated segment of a porcine VN and carotid artery as a reference. A quasitrapezoidal current-controlled pulse (stimulus) was applied to the VN or arterial segment using an appointed group of three electrodes (triplet). The triplet and stimulus were configured to predominantly stimulate B-fibers and minimize the stimulation of A-fibers. The EIS results revealed capacitive charge transfer predominance, which is a highly desirable property. Electrophysiological performance testing indicated the potential existence of certain parameters and waveforms of the stimulus for which the contribution of the A-fibers to the NR decreased slightly and that of the B-fibers increased slightly. Findings show that the design of the stimulating electrodes, based on the EIS and ECM results, could act as a useful tool for nerve cuff development.

The effect of sol–gel boehmite coatings on the corrosion and decarburization of C45 steel

AbstractSol–gel boehmite coatings were produced on the polished surfaces of hypo-eutectoid C45carbon steel by dip coating. After the deposition the coatings were heat treated by drying at RT, 150 and 200 °C. It was found that for crack-free coatings, the drying temperature needs to be ≥150 °C. Properly heat-treated boehmite coatings then improve the corrosion resistance of steel, while proposed alumina coatings derived from the boehmite coatings during annealing of the steel affect the decarburization. The coated steel samples were annealed at temperatures that are typical for the heat-treatment and thermomechanical process of C45 steel, i.e., AC3 (austenitization, thermomechanical process). The sol–gel alumina coating decreased the decarburization rate of the quenched steel during the tempering (≤600 °C), which meant that the hardness reduction on the steel surface was smaller. Alumina coatings have a smaller effect on the decarburization at higher temperatures; however, the metallographic analyses indicate that the coatings can retard the oxidation rate in comparison to the decarburization rate and thus, somewhat increase the visual level of the decarburization. Under annealing conditions (T = 950 °C, t = 0.5–2 h) at which the oxidation rate is higher than the decarburization rate the decarburization process is not important since the decarburized layer is peeled off the steel surface together with the scale. No visual decarburization is then observed.

The mechanics behind formation of secondary ledeburite during tool steel welding

In this article we describe the microstructural changes in the heat affected zone (HAZ) of the tool steel W. Nr. 1.2379, which was surfaced or welded by the submerged arc welding technique (SAW) with different welding parameters. Microstructure of the welds and of the surfacing welds was analysed by optical and scanning electron microscope. In this research, we particularly studied microstructural changes in the area of primary chromium carbides in the HAZ and their effect on the weld crystalization. We came to the conclusion that the temperature in the HAZ is high enough during the welding process that it caused primary carbides to dissolve and concentration of the carbide-forming elements and carbon increased in the surrounding austenite matrix area to eutectic composition, which remelts and solidified as secondary eutectic (ledeburite).