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Boron as thin film material is of relevance for use in modern micro- and nano-fabrication technology. In this research boron thin films are realized by a number of physical and chemical deposition methods, including magnetron sputtering, electron-beam evaporation, plasma enhanced chemical vapor deposition (CVD), thermal/non-plasma CVD, remote plasma CVD and atmospheric pressure CVD. Various physical, mechanical and chemical characteristics of these boron thin films are investigated, i.e., deposition rate, uniformity, roughness, stress, composition, defectivity and chemical resistance. Boron films realized by plasma enhanced chemical vapor deposition (PECVD) are found to be inert for conventional wet chemical etchants and have the lowest amount of defects, which makes this the best candidate to be integrated into the micro-fabrication processes. By varying the deposition parameters in the PECVD process, the influences of plasma power, pressure and precursor inflow on the deposition rate and intrinsic stress are further explored. Utilization of PECVD boron films as hard mask for wet etching is demonstrated by means of patterning followed by selective structuring of the silicon substrate, which shows that PECVD boron thin films can be successfully applied for micro-fabrication. [ABSTRACT FROM AUTHOR]

The role of the Mo2C/oxide interface on multi-layer graphene (MLG) nucleation during a chemical vapor deposition (CVD) process is investigated. During the CVD process, MLG growth is only observed in the presence of a Mo2C/SiO2 interface, indicating that the chemical reactions occurring at this interface trigger the nucleation of MLG. The chemical reaction pathway is explained in four steps as (1) creation of H radicals, (2) reduction of the oxide surface, (3) formation of C–C bonds at O–H sites, and (4) expansion of graphitic domains on the Mo2C catalyst. Different Mo2C/oxide interfaces are investigated, with varying affinity for reduction in a hydrogen environment. The results demonstrate a catalyst/oxide bifunctionality on MLG nucleation, comprising of CH4 dehydrogenation by Mo2C and initial C–C bond formation at the oxide interface. [ABSTRACT FROM AUTHOR]

Recent advances in brain-on-a-chip technology have led to the development of modified microelectrode arrays. Previously, the authors have contributed to this exciting field of neuroscience by demonstrating a fabrication process for producing microsieve chips that contain three-dimensional (3D) micropores at the electrodes [termed microsieve electrode arrays (µSEAs)]. This chip allows us to trap hundreds of single neuronal cells in parallel onto the electrodes [B. Schurink and R. Luttge, J. Vac. Sci. Technol., B 31, 06F903 (2013)]. However, trapping the neurons reproducibly under gentle, biocompatible conditions remains a challenge. The current setup involves the use of a hand-operated syringe that is connected to the back of the µSEA chip with a polydimethylsiloxane (PDMS) construct. This makes the capture process rather uncontrolled, which can lead to either cell damage by shear stress or the release of trapped neurons when unplugging the syringe and PDMS constructs. Although, the authors could achieve an efficient capture rate of single neurons within the 3D micropores (80%-90% filling efficiency), cell culture performance varied significantly. In this paper, the authors introduce a passive pumping mechanism for the parallel trapping of neurons onto the µSEA chip with the goal to improve its biological performance. This method uses the capillary pumping between two droplets (a "pumping droplet" on one side of the chip and a "reservoir droplet" on the other side) to create a stable and controllable flow. Due to simplification of the handling procedure, omitting the use of a syringe and additional connections to the µSEA chip, the set-up is compatible with real time microscopy techniques. Hence, the authors could use optical particle tracking to study the trapping process and record particle velocities by video imaging. Analyzing the particle velocities in the passive pumping regime, the authors can confirm a gentle uniform particle flow through the 3D micropores. The authors show that passive pumping particle velocity can be tightly controlled (from 5 to 7.5 to 10.4 µm/s) simply by changing the droplet volume of the pumping droplets from 20, 40, and 60 µl and keeping the reservoir drop constant (10 µl). The authors demonstrate that neuron capturing efficiency and reproducibility as well as neuronal network formation are greatly improved when using this passive pumping approach. [ABSTRACT FROM AUTHOR]

Commercial microelectrode arrays (MEAs) for in vitro neuroelectrophysiology studies rely on conventional two dimensional (2D) neuronal cultures that are seeded on the planar surface of such MEAs and thus form a random neuronal network. The cells attaching on these types of surfaces grow in 2D and lose their native morphology, which may also influence their neuroelectrical behavior. Besides, a random neuronal network formed on this planar surface in vitro also lacks comparison to the in vivo state of brain tissue. In order to improve the present MEA platform with the above mentioned concerns, in this paper, the authors introduce a three dimensional platform for neuronal cell culturing, where a linear nanoscaffold is patterned on a microsieve array by displacement Talbot lithography (DTL) and reactive ion etching. Good pattern uniformity is achieved by the DTL method on the topographically prepatterned nonflat surface of the microsieve array. Primary cortical cells cultured on the nanopatterned microsieve array show an organized network due to the contact guidance provided by the nanoscaffold, presenting 47% of the total outgrowths aligning with the nanogrooves in the observed view of field. Hence, the authors state that this nanopatterned microsieve array can be further integrated into microsieve-based microelectrode arrays to realize an advanced Brain-on-Chip model that allows us to investigate the neurophysiology of cultured neuronal networks with specifically organized architectures. [ABSTRACT FROM AUTHOR]

In this contribution, the authors present our advances in three-dimensional (3D) neuronal cell culture platform technology contributing to controlled environments for microtissue engineering and analysis of cellular physiological and pathological responses. First, a micromachined silicon sieving structure is presented as key parameter for a modified version of a planar tissue culture, allowing seeding of single neurons in pyramidal shaped pores by a hydrodynamic sieve flow. Second, a nanogroove-hydrogel interface is presented as a more biomimetic in vivo representation of neuronal tissues, where 3D culturing is required to reproduce the layered tissue organization, which is observed in the microenvironment of the brain. To further our understanding of uniquely nanopatterned interfaces, the authors evaluated 3D neuronal outgrowth into Matrigel atop of primary cortical cell (CTX) cultured on nanogrooves. The interface facilitates conformation of cell somas and aligned outgrowth in 3D with outgrowth alignment preserved in Matrigel up to 6 μm above the nanogrooved substrate, which has a pattern height of just 108 nm. Finally, with the view to incorporate these guided culture interfaces in our previously designed hybrid Polydimethylsiloxane bioreactor, the authors have also explored 3D cellular culture matrix as a variable in such systems. By analyzing the effect of different gel matrices (Matrigel, PuraMatrix, and collagen-I) on the neuron model cell line SH-SY5Y, the authors bring together the ability to guide neuronal growth in spatially standardized patterns and within a bioreactor potentially coupled to an array of single cells that could facilitate readout of such complex cultures by integration with existing technologies (e.g., microelectrode arrays). Various combinations of these novel techniques can be made and help to design experimental studies to investigate how changes in cell morphology translate to changes in function but also how changes in connectivity relate to changes in electrophysiology. These latest advancements will lead to the development of improved, highly organized in vitro assays to understand, mimic, and treat brain disorders. [ABSTRACT FROM AUTHOR]

Networks of neurons cultured on-chip can provide insights into both normal and disease-state brain function. The ability to guide neuronal growth in specific, artificially designed patterns allows us to study how brain function follows form. Primary cortical cells cultured on nanograting scaffolds, in particular astrocytes, showed highly ordered regions of dendritic outgrowth. Usually, materials suitable for nanopatterning have a stiffness far above that of the extracellular matrix. In this paper, the authors studied two materials with large differences in stiffness, polydimethylsiloxane (PDMS) and silicon. Our results show that both nanopatterned silicon and PDMS guide the outgrowth of astrocytes in cortical cell culture, but the growth of the astrocyte is affected by the stiffness of the substrate, as revealed by differences in the cell soma size and the organization of the outgrowth. [ABSTRACT FROM AUTHOR]

The authors present a hydrogel/poly-dimethylsiloxane (PDMS) hybrid bioreactor. The bioreactor enables a low shear stress 3D culture by integrating a hydrogel as a barrier into a PDMS casing. The use of PDMS allows the reversible adhesion of the device to a commercially available microelectrode array. A two-step molding process facilitates this relatively simple, cost effective, and leakage-free add-on microculture system. Agarose (2%) is used as hydrogel barrier material and mass transport is evaluated by fluorescein isothiocyanate-albumin fluorescence under static conditions which yields a diffusion coefficient of average value of 2.2 × 10-7 cm2 s-1 across the barrier. To validate our bioreactor for diffusion limited 3D cell culture, rat cortical cells were successfully cultured in Matrigel for 6 days. [ABSTRACT FROM AUTHOR]