Ultra-flexible electrode arrays with a cross-sectional area of only a few µm² show great promise for long-term, high resolution neural interfacing without detrimental scar tissue formation. However, due to their low stiffness, insertion is a challenge. In this work, we investigate microneedles consisting of quickly biodegradable, short-chained, acid terminated PLGA (50:50 lactide:glycolide ratio) as insertion device for a polyimide-based neural electrode array of 1 µm thickness. An upscalable, wafer-level fabrication process is presented. Both separate PLGA microneedles as well as complete, assembled neural probes were tested in vivo for up to 4 months. The arrays allowed to record spontaneous spike activity and evoked local field potentials in the somatosensory cortex of rats on all measured timepoints. Very limited lesion formation, measuring about 20% of the cross sectional area of the original microneedle, was observed. Neurons can be seen to infiltrate the area originally taken up by the dissolving PLGA microneedle. The results indicate that the presented electrode arrays and insertion method are well suitable for application in long-term, high resolution neural recording.
High-power electronics in the transportation and aerospace sectors need size and weight reduction. Multifunctional and multistructured materials are currently being developed to couple electromagnetic (EM) and thermal properties, i.e., shielding against electromagnetic impulsions, and thermal management across the thermal interface material (TIM). In this work, we investigate laser-machined patterned carbon nanotube (CNT) micro-brushes as an alternative to metallic structures for driving simultaneously EM and heat propagation. The thermal and electromagnetic response of the CNT array is expected to be sensitive to the micro-structured pattern etched in the CNT brush.
Gas sensing can be performed by fingerprinting their field ionization characteristics. This paper presents the development of a miniaturized ionization sensor using ion-track etched polyimide as structural layer and template for Ni nanowires synthesis. The device consists in two parallel plate electrodes with gaps varying from 5 to 12 µm. The nanowires impact on breakdown voltage has been analyzed during first electrical characterizations and I-V curves measurements. For a 5.5 µm-gap, breakdown voltage is reduced from 320 to 80 V with a corresponding current at least three order of magnitude lower. Using the sensor in harsh environments such as space applications is also discussed. Miniaturized ionization sensors are powerful candidates as integrated universal gas sensor based on pattern recognition for environmental monitoring. Such a system should be easily integrated in picosatellites such as CubeSats dedicated to the physical analysis of low thermosphere composition.
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