Brazing techniques for the fabrication of biocompatible carbon-based electronic devices

Prototype electronic devices have been critical to the discovery and demonstration of the unique properties of new materials, including composites based on carbon nanotubes (CNT) and graphene. However, these devices are not typically constructed with durability or biocompatibility in mind, relying on conductive polymeric adhesives, mechanical clamps or crimps, or solders for electrical connections. In this paper, two key metallization techniques are presented that employ commercially-available brazing alloys to fabricate electronic devices based on diamond and carbonaceous wires. Investigation of the carbon - alloy interfacial interactions was utilized to guide device fabrication. The interplay of both chemical ( adhesive ) and mechanical ( cohesive ) forces at the interface of different forms of carbon was exploited to fabricate either freestanding or substrate-fixed carbonaceous electronic devices. Elemental analysis in conjunction with scanning electron microscopy of the carbon - alloy interface revealed the chemical nature of the Ag alloy bond and the mechanical nature of the Au alloy bond. Electrical characterization revealed the non-rectifying nature of the carbon - Au alloy interconnects. Finally, electronic devices were fabricated, including a Au circuit structure embedded in a polycrystalline diamond substrate

Soft, flexible freestanding neural stimulation and recording electrodes fabricated from reduced graphene oxide

There is an urgent need for conductive neural interfacing materials that exhibit mechanically compliant properties, while also retaining high strength and durability under physiological conditions. Currently, implantable electrode systems designed to stimulate and record neural activity are composed of rigid materials such as crystalline silicon and noble metals. While these materials are strong and chemically stable, their intrinsic stiffness and density induce glial scarring and eventual loss of electrode function in vivo. Conductive composites, such as polymers and hydrogels, have excellent electrochemical and mechanical properties, but are electrodeposited onto rigid and dense metallic substrates. In the work described here, strong and conductive microfibers (40-50 μm diameter) wet-spun from liquid crystalline dispersions of graphene oxide are fabricated into freestanding neural stimulation electrodes. The fibers are insulated with parylene-C and laser-treated, forming brush electrodes with diameters over 3.5 times that of the fiber shank. The fabrication method is fast, repeatable, and scalable for high-density 3D array structures and does not require additional welding or attachment of larger electrodes to wires. The electrodes are characterized electrochemically and used to stimulate live retina in vitro. Additionally, the electrodes are coated in a water-soluble sugar microneedle for implantation into, and subsequent recording from, visual cortex

On Transient qualification of LOBI/MOD2, SPES, LSTF and BETHSY nodalizations for RELAP5/MOD2 code

The results obtained in a more-than-a-decade application of thermal-hydraulic system codes to the analysis of experiments performed in Integral Test Facilities (ITF) and Separate Effect test Facilities (SETF) including the participation to several International Standard Problems (ISP) and Standard Problem Exercises (SPE), organized by OECD/NEA/CSNI (Organization for Economic Cooperation and Development / Nuclear Energy Agency / Committee on the Safety of Nuclear Installations) and by IAEA (international Atomic Energy Agency), respectively, suggested the need for new methods and procedures for code application. The words nodalization-qualification, qualitative-accuracy-evaluation, quantitative-accuracy-evaluation, and acceptability-thresholds were introduced. The present document deals with nodalization qualification at the transient level for the LOBI/mod2 available at the EURATOM JRC of Ispra (Italy), the SPES, available at the SIET research center in Piacenza, Italy, the LSTF available at the Tokai-Mura Research Center of JAERI in Japan and the BETHSY available at the CEA-CENG research center in Grenoble, France. The activity in this case is based upon the analysis of one experiment performed in each ITF, respectively: criteria for accepting the results of the comparison with calculated data are fixed from the application of the FFTBM (Fast Fourier Transform Based Method)

Summary of results.

<p>Summary of results.</p

Recovery of model parameters for a sample cell.

<p>(a) The stimuli are projected onto the first two principal components, and . The grey squares represent the spike probability, where a black value represents 0 probability, and a white value represents a probability of 1. Plotted above and to the right are the histograms of the stimuli (gray) and the spike-triggered stimuli (black) along each component axis. (b) Eigenvalues of the spike-triggered stimuli recovered by principal component analysis (round circles) are plotted. The eigenvalues are normalized by the variance of the input stimuli. The shaded region represents the 95% confidence interval from the statistical hypothesis test. The hypothesis test recovered one significant excitatory and one significant suppressive component. The red arrows show the distance between the two most significant eigenvalues and the mean of the random distribution recovered from the first iteration of the hypothesis test. The length of the arrows represent <i>d</i>₁ and <i>d</i>₂ from Eq (<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1004849#pcbi.1004849.e057" target="_blank">10</a>). (c) The nonlinear function recovered by fitting a double sigmoid to the spike probability projected onto and . Open circles represent the raw data and the solid line shows the nonlinear equation fit (r² = 0.98). This cell had a positive and negative threshold (parameters <i>c</i>₊ and <i>c</i>₋ in Eq (<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1004849#pcbi.1004849.e017" target="_blank">5</a>)) of 129 μA and -152 μA proportional to and , respectively. (d) The true and (solid black) are compared to the root mean square (dashed line) of a distribution of and (gray). Stars show which electrodes were significant. In this preparation, electrode 12 was not operational. (e) Representation of the amplitudes that generate the ERFs, (left) and (right). The large circles represent the electrode locations. A correlation coefficient of -0.97 was obtained between and . Three electrodes significantly affected the cell in and in . In this experiment, the retina was placed such that the optic disc was located around electrode 9. The stimulation return electrode was placed distally above electrode 12. The green circle shows the approximate dendritic field of the recorded cell. Stimulus amplitudes ranged up to ±300 μA; however, the range shown here is smaller to make the differences in electrode amplitudes clearer.</p

Recovery of the spike-triggered stimuli for the spike-triggered covariance (STC) analysis.

<p>(a) Discretized sequence of the neural response and stimulus. Each stimulus consists of a combination of biphasic pulses applied to all 20 electrodes. Stimuli that evoked a spike in the neuron are recorded in the stimulus matrix <b>S</b>_D. (b) STC was conducted on the stimuli generating a response, <b>S</b>_D, to separate the stimulus space into a positive and negative region (+ and ×). The x-axis corresponds to the first eigenvector (); the y-axis corresponds to the second eigenvector (). Not all stimuli generated a response in the neuron. Shown in black are the total applied stimuli, <b>S</b>_T, which are overlaid by stimuli <b>S</b>_D (white crosses). Also shown are the projections of the electrical receptive fields, (large diamond) and (large circle).</p

Sample of the diverse varieties of ERFs.

<p>Each numbered block represents the ERFs from a single cell. The ERFs in red represent suppressive components. The arrow represents the direction of time for each plot, with stimulus frames separated in time according to the stimulation frequency. Cells 1–4 were stimulated at 10 Hz, cells 5–7 at 20 Hz, and cells 8–9 at 30 Hz. Only significant electrode amplitudes are shown, and all significant electrodes are visible. Stimulating electrodes are separated by 1 mm center-to-center.</p

Electrical receptive field properties.

<p>A) Proportions of cells with up to three excitatory components. B) Proportions of cells with up to three suppressive components. C). The temporal windows over which suppressive and excitatory ERFs affected cell responses, thus indicating duration of stimulus integration time. Excitatory ERFs tended to occur within a short latency from the response (blue circles). Suppressive ERFs tended to extend over a long duration, which was variable from cell to cell (orange circles). The squares represent the means for all cells. D) RGC preference to cathodic-first or anodic-first stimulation. Squares represent means and lines indicate ±1 standard deviation. Stars denote significant differences (<i>p</i> < 0.05).</p