Entwicklung eines LIGA-Mikrosystems zur Messung mechanischer Eigenschaften von Mikroproben

Wissenschaftlliche Berichte - FZKA 5986 Bei der Entwicklung der Mikroelektronik standen zunächst nur die elektrischen und thermischen Materialkenndaten im Vordergrund. Im Zuge der Weiterentwicklung zur Mikrosystemtechnik, bei der mikromechanische Komponenten mit der entsprechenden Auswerteelektronik kombiniert werden, ergibt sich die Notwendigkeit, daß auch die mechanischen Materialeigenschaften der verwendeten Werkstoffe bekannt sind. Da diese Kenndaten aufgrund der spezifischen Herstellungsverfahren der Mikrosystemtechnik und charakteristischer Dimensionen nicht ohne weiteres von der Makromechanik auf Dimensionen im Mikrometerbereich übertragen werden können, müssen sie an mikrostrukturierten Proben ermittelt werden. Um die Handhabung der Mikroproben hinsichtlich Montage und Justage bei der Materialprüfung zu erleichtern, wurde in der vorliegenden Arbeit ein Prüfsystem entwickelt, dessen laterale Dimensionen mit denjenigen des Prüflings vergleichbar sind. Mit diesem sog. Mikroprüfsystem wird der Elastizitäts-Modul von Mikrobalken in einem Biegeexperiment ermittelt. Das Prüfsystem besteht aus einem Mikroaktor mit integriertem Kraftsensor auf der Basis von Dehnmeßstreifen (DMS), einer optischen Wegmeßeinheit und einer Probenhalterung. Es stellt das erste nach dem LIGA-Verfahren gefertigte Mikrosystem dar, das fluidische Aktorik mit optischer und elektrischer Sensorik kombiniert. Die Gesamtabmessungen des Systems betragen 6.5 x 4.5 mm2 bei einer Strukturhöhe von ca. 250 µm. Für die Realisierung einer optimierten Fluidankopplung wurde das LIGA-Verfahren mit dem hierfür entwickelten Opferstrukturverfahren kombiniert. Die DMS werden über einen neuen, zum LIGA-Verfahren kompatiblen Herstellungsprozeß gefertigt, bei dem zunächst die DMS auf dem Substrat realisiert und anschließend die Mikrostrukturen auf diesen galvanisch aufgebaut werden. Für das Mikroprüfsystem wurde ein druckbetriebener Mikroaktor entwickelt, der Prüfkräfte im Bereich mehrerer 10 mN auf die Mikrobalken übertragen kann. Er besteht aus einer Aktorkammer und einem beweglichen Kolben, der sich aufgrund einer Druckdifferenz zwischen Kammer und Außenraum parallel zum Substrat bewegen kann. Wesentlicher Vorteil im Vergleich zu bestehenden Mikroaktoren ist, daß die übertragbaren Kräfte unabhängig vom Stellweg des Kolbens sind. Um die am Prüfling angreifenden Kräfte ermitteln zu können, wurden Kraftsensoren auf dem Kolben integriert. Dabei handelt es sich um DMS, die die Relativbewegung einer beweglichen Komponente innerhalb des beweglichen Kolbens detektieren. Die Wegmeßeinheit ermittelt die Balkenverbiegung indirekt über den Stellweg des Kolbens. Ihr Funktionsprinzip beruht auf der Reflexion eines divergenten Lichtstrahls an einem beweglichen Spiegel und der entsprechenden Detektion der reflektierten Lichtintensität als Funktion der Spiegelposition. Die Ankopplung der Mikrostruktur an die erforderliche Lichtquelle und Detektoren erfolgt über Lichtleitfasern. Die Balkenverbiegung kann mit diesem optischen Meßaufnehmer mit einer Genauigkeit von 200 nm bestimmt werden. Alternativ zum Einsatz des druckbetriebenen Mikroaktors im Mikroprüfsystem konnte dessen mögliche Anwendung in der minimal invasiven Chirurgie nachgewiesen werden. Dabei wird der Aktor die Antriebseinheit für ein Schneidwerkzeug auf einem Herzkatheter bilden

In vivo Recording Quality of Mechanically Decoupled Floating Versus Skull-Fixed Silicon-Based Neural Probes

Throughout the past decade, silicon-based neural probes have become a driving force in neural engineering. Such probes comprise sophisticated, integrated CMOS electronics which provide a large number of recording sites along slender probe shanks. Using such neural probes in a chronic setting often requires them to be mechanically anchored with respect to the skull. However, any relative motion between brain and implant causes recording instabilities and tissue responses such as glial scarring, thereby shielding recordable neurons from the recording sites integrated on the probe and thus decreasing the signal quality. In the current work, we present a comparison of results obtained using mechanically fixed and floating silicon neural probes chronically implanted into the cortex of a non-human primate. We demonstrate that the neural signal quality estimated by the quality of the spiking and local field potential (LFP) recordings over time is initially superior for the floating probe compared to the fixed device. Nonetheless, the skull-fixed probe also allowed long-term recording of multi-unit activity (MUA) and low frequency signals over several months, especially once pulsations of the brain were properly controlled

Planar-type silicon thermoelectric generator with phononic nanostructures for 100 {\mu}W energy harvesting

Energy harvesting is essential for the internet-of-things networks where a tremendous number of sensors require power. Thermoelectric generators (TEGs), especially those based on silicon (Si), are a promising source of clean and sustainable energy for these sensors. However, the reported performance of planar-type Si TEGs never exceeded power factors of 0.1 ${\mu} Wcm^{-2} K^{-2}$ due to the poor thermoelectric performance of Si and the suboptimal design of the devices. Here, we report a planar-type Si TEG with a power factor of 1.3 ${\mu} Wcm^{-2} K^{-2}$ around room temperature. The increase in thermoelectric performance of Si by nanostructuring based on the phonon-glass electron-crystal concept and optimized three-dimensional heat-guiding structures resulted in a significant power factor. In-field testing demonstrated that our Si TEG functions as a 100-${\mu}W$-class harvester. This result is an essential step toward energy harvesting with a low-environmental load and cost-effective material with high throughput, a necessary condition for energy-autonomous sensor nodes for the trillion sensors universe

In vivo validation of the electronic depth control probes.

In this article, we evaluated the electrophysiological performance of a novel, high-complexity silicon probe array. This brain-implantable probe implements a dynamically reconfigurable voltage-recording device, coordinating large numbers of electronically switchable recording sites, referred to as electronic depth control (EDC). Our results show the potential of the EDC devices to record good-quality local field potentials, and single- and multiple-unit activities in cortical regions during pharmacologically induced cortical slow wave activity in an animal model

Oscillatory activity in the medial prefrontal cortex and nucleus accumbens correlates with impulsivity and reward outcome.

Actions expressed prematurely without regard for their consequences are considered impulsive. Such behaviour is governed by a network of brain regions including the prefrontal cortex (PFC) and nucleus accumbens (NAcb) and is prevalent in disorders including attention deficit hyperactivity disorder (ADHD) and drug addiction. However, little is known of the relationship between neural activity in these regions and specific forms of impulsive behaviour. In the present study we investigated local field potential (LFP) oscillations in distinct sub-regions of the PFC and NAcb on a 5-choice serial reaction time task (5-CSRTT), which measures sustained, spatially-divided visual attention and action restraint. The main findings show that power in gamma frequency (50-60 Hz) LFP oscillations transiently increases in the PFC and NAcb during both the anticipation of a cue signalling the spatial location of a nose-poke response and again following correct responses. Gamma oscillations were coupled to low-frequency delta oscillations in both regions; this coupling strengthened specifically when an error response was made. Theta (7-9 Hz) LFP power in the PFC and NAcb increased during the waiting period and was also related to response outcome. Additionally, both gamma and theta power were significantly affected by upcoming premature responses as rats waited for the visual cue to respond. In a subgroup of rats showing persistently high levels of impulsivity we found that impulsivity was associated with increased error signals following a nose-poke response, as well as reduced signals of previous trial outcome during the waiting period. Collectively, these in-vivo neurophysiological findings further implicate the PFC and NAcb in anticipatory impulsive responses and provide evidence that abnormalities in the encoding of rewarding outcomes may underlie trait-like impulsive behaviour.RCUK, Wellcome, OtherThis is the final version of the article. It first appeared at http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0111300

A Wireless Multi-Channel Recording System for Freely Behaving Mice and Rats

To understand the neural basis of behavior, it is necessary to record brain activity in freely moving animals. Advances in implantable multi-electrode array technology have enabled researchers to record the activity of neuronal ensembles from multiple brain regions. The full potential of this approach is currently limited by reliance on cable tethers, with bundles of wires connecting the implanted electrodes to the data acquisition system while impeding the natural behavior of the animal. To overcome these limitations, here we introduce a multi-channel wireless headstage system designed for small animals such as rats and mice. A variety of single unit and local field potential signals were recorded from the dorsal striatum and substantia nigra in mice and the ventral striatum and prefrontal cortex simultaneously in rats. This wireless system could be interfaced with commercially available data acquisition systems, and the signals obtained were comparable in quality to those acquired using cable tethers. On account of its small size, light weight, and rechargeable battery, this wireless headstage system is suitable for studying the neural basis of natural behavior, eliminating the need for wires, commutators, and other limitations associated with traditional tethered recording systems

Root-emitted volatile organic compounds: can they mediate belowground plant-plant interactions?

peer reviewedBackground Aboveground, plants release volatile organic compounds (VOCs) that act as chemical signals between neighbouring plants. It is now well documented that VOCs emitted by the roots in the plant rhizosphere also play important ecological roles in the soil ecosystem, notably in plant defence because they are involved in interactions between plants, phytophagous pests and organisms of the third trophic level. The roles played by root-emitted VOCs in between- and within-plant signalling, however, are still poorly documented in the scientific literature. Scope Given that (1) plants release volatile cues mediating plant-plant interactions aboveground, (2) roots can detect the chemical signals originating from their neighbours, and (3) roots release VOCs involved in biotic interactions belowground, the aim of this paper is to discuss the roles of VOCs in between- and within-plant signalling belowground. We also highlight the technical challenges associated with the analysis of root-emitted VOCs and the design of experiments targeting volatile-mediated root-root interactions. Conclusions We conclude that root-root interactions mediated by volatile cues deserve more research attention and that both the analytical tools and methods developed to study the ecological roles played by VOCs in interplant signalling aboveground can be adapted to focus on the roles played by root-emitted VOCs in between- and within-plant signalling