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In the last decades, planar multi-electrode arrays (MEAs) have been widely used to record activity from in vitro neuronal cell cultures and tissue slices. Though successful, this technique bears some limitations, particularly relevant when applied to three-dimensional (3D) tissue, such as brain slices, spheroids or organoids. For example, planar MEAs signals are informative on just one side of a 3D-organized structure. This limits the interpretation of the results in terms of network functions in a complex structured and hyperconnected brain tissue. Moreover, the side in contact with the MEAs often shows lower oxygenation rates and related vitality issues. To overcome these problems, we empowered a CMOS high-density multi-electrode array (HD-MEA) with thousands of microneedles (μneedles) of 65-90 μm height, able to penetrate and record in-tissue signals, providing for the first time a 3D HD-MEA chip. We propose a CMOS-compatible fabrication process to produce arrays of μneedles of different widths mounted on large pedestals to create microchannels underneath the tissue. By using cerebellar and cortico-hippocampal slices as a model, we show that the μneedles efficiently penetrate the 3D tissue while the microchannels allow the flowing of maintenance solutions to increase tissue vitality in the recording sites. These improvements are reflected by the increase in electrodes sensing capabilities, the number of sampled neuronal units (compared to matched planar technology), and the efficiency of compound effects. Importantly, each electrode can also be used to stimulate the tissue with optimal efficiency due to the 3D structure. Furthermore, we demonstrate how the 3D HD-MEA can efficiently penetrate and get outstanding signals from in vitro 3D cellular models as brain spheroids. In conclusion, we describe a new recording device characterized by the highest spatio-temporal resolution reported for a 3D MEA and significant improvements in the quality of recordings, with a high signal-to-noise ratio and improved tissue vitality. The applications of this game-changing technique are countless, opening unprecedented possibilities in the neuroscience field and beyond.

Recently lithium niobate on insulator (LNOI) has emerged as a promising platform for photonic integrated circuits (PICs) owing to the material’s high second order nonlinearity, a large transparency window and high piezo electric coefficients. Published results on LNOI range from efficient electro-optic modulators [1] to broadband supercontinua [2] – [4] . However, lithium niobate has a comparably high sensitivity towards optical damage processes such as photorefractive damage [5] , [6] . Their exact mechanisms are not yet fully understood and the impact on the long-term stability of LNOI devices has not yet been examined. Here, we present long-term measurements showing that during 400 hours of continuous irradiation with a mode-locked laser the supercontinuum spectrum remains stable.

We demonstrate that lithium niobate integrated photonics allows for reliable nonlinear applications under continuous femtosecond laser irradiation. Over >100 hours, a stable octave-spanning supercontinuum plus second-harmonic generation allows for direct self-referencing of a frequency comb.

The paper describes the fabrication of a silicon carbide piezoresistive pressure sensors intended for operating temperatures of up to 600°C. The different fabrication aspects, such as the metallization scheme, the etching of a 300μm deep cavity, and the bonding to a silicon carbide back plate are discussed in detail.

Microstencil lithography, i.e. local deposition of micrometer scale patterns through small shadow masks, is a promising method for metal micropattern definition on polymer substrates that cannot be structured using organic-solvent-based photoresist technology. We propose to apply microstencil lithography to fabricate microelectrodes on flat and 3D polymer substrates, such as PMMA or SU-8, which form parts of microfluidic systems with integrated microelectrodes. Microstencil lithography is accompanied by two main issues when considered for application as a low-cost, reproducible alternative to standard photolithography on polymer substrates. In this paper we assess in detail (i) the reduction of aperture size (clogging) after several metal evaporation steps and corresponding change of deposited pattern size and (ii) loss in the resolution (blurring) of the deposited microstructures when there is a several micrometers large gap between the stencil membrane and the substrate. The clogging of stencil apertures induced by titanium and copper evaporation was checked after each evaporation step, and it was determined that approximately 50% of the thickness of the evaporated metals was deposited on the side walls of the stencil apertures. The influence of a gap on the deposited structures was analyzed by using 18 um thick SU-8 spacers placed between the microstencil and the substrate. The presence of an 18 um gapmade the deposited structures notably blurred. The blurring mechanism of deposited structures is discussed based on a simplified geometrical model. The results obtained in this paper allow assessing the feasibility of using stencil-based lithography for unconventional surface patterning, which shows the limits of the proposed method, but also provides a guideline on a possible implementation for combined polymer-electrode microsystems, where standard photoresist technology fails.