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ref: -0 tags: tungsten eletropolishing hydroxide cleaning bath tartarate date: 03-28-2017 16:34 gmt revision:0 [head]

Method of electropolishing tungsten wire US 3287238 A

  • The bath is formed of 15% by weight sodium hydroxide, 30% by weight sodium potassium tartrate, and 55% by weight distilled water, with the bath temperature being between 70 and 100 F.
    • If the concentration of either the hydroxide or the tartrate is below the indicated minimum, the wire is electrocleaned rather than electropolished, and a matte finish is obtained rather than a specular surface.
    • If the concentration of either the hydroxide or the tartrate is greater than the indicated maximum, the electropolishing process is quite slow.
  • The voltage which is applied between the two electrodes 18 and 20 is from 16 to 18.5 volts, the current through the bath is 20 to 24 amperes, and the current density is 3,000 to 4,000 amperes per square foot of surface of wire in the bath.

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ref: -0 tags: intracellular juxtacellular recording tungsten nanowire whole cell patch date: 02-06-2017 22:39 gmt revision:2 [1] [0] [head]

PMID-22905231 Neuronal recordings with solid-conductor intracellular nanoelectrodes (SCINEs).

  • <300 nm diameter W fibers, several um long, fabricated via FIB.
  • Functionalized with a hydrophobic silane on the oxide.
    • Quite complete & custom methods here.
  • Not quite whole cell recording, but excellent SNR; 4mv APs.
    • Slice, rat hippocampus organotypic.
    • Expected much larger recorded APs; suspect partial membrane penetration.
    • Only lasted a few seconds to minutes.
  • Needed custom recording setup for interfacing with 100Gohm electrodes; stray capacitance < 4 pf.
  • Intracellular electrodes must be designed to not shunt the membrane open upon insertion.
    • In a study where whole-cell recordings were established prior sharp microelectrode penetration, all neurons showed significant depolarization following impalement.
    • Here there was no change in membrane voltage in 10% of insertions of the silane-functionalized SCINEs. only in the functionalized electrodes).
    • Minor distortion of the AP was observed.
  • In whole-cell patch clamping, diffusion from the pipette to the cytosol interrupts biochemical processes necessary for normal cellular function (e.g. respiration!).
  • The hardness of the tungsten ensures that SCINEs can be repeatedly inserted millimeter-deep into brain tissue without noticeable damage to the tip.
    • E.g. 300 nm tungsten will not easily navigate vasculature...

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ref: -0 tags: tungsten rhenium refactory metals book russia metalurgy date: 10-31-2016 05:14 gmt revision:1 [0] [head]

Physical Metallurgy of Refactory Metals and Alloys

Properties of tungsten-rhenium alloys

  • Luna metals suggests 3% Re improves the tensile strength of the alloy; Concept Alloys has 26% Re.
  • This paper mesured 20% Re, with a strength of 1.9 GPa; actual drawn tungsten wire has a strength of 3.3 GPa.
    • Drawing and cold working greatly affects metal, as always!

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ref: -2008 tags: tantalum chromium polyimide tungsten flexible neural implants adhesion layer date: 06-24-2015 22:53 gmt revision:2 [1] [0] [head]

PMID-18640155 Characterization of flexible ECoG electrode arrays for chronic recording in awake rats.

  • Yeager JD1, Phillips DJ, Rector DM, Bahr DF.
  • We tested several different adhesion techniques including the following: gold alone without an adhesion layer, titanium-tungsten, tantalum and chromium.
  • All films were DC magnetron sputtered, without breaking vacuum between the adhesion layer (5nm) and gold counductor layer (300nm).
  • We found titanium-tungsten to be a suitable adhesion layer considering the biocompatibility requirements as well as stability and delamination resistance.
  • While chromium and tantalum produced stronger gold adhesion, concerns over biocompatibility of these materials require further testing.
    • Thought: use tantalum directly, no Ti needed.
    • Much better than Cr -- much more ductile and biocompatible.
    • Caveat: studies showing reduction to stociometric Ta results in delamination.
  • Ta conductivity: 1.35e-7 Ohms * m; Ti 4.2e-7; 3x better (film can be 3x thinner..)

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ref: -0 tags: tungsten welding CVD arc braze 1971 date: 08-12-2014 20:56 gmt revision:0 [head]

Weldability of Tungsten and Its Alloys

  • tried relatively exotic brazing methods:
    • Niobium,
    • Tantalum
    • W - 26% Re
    • Mo
      • No mention of what we'll be doing (NiCr resistance wire -- only easily available fine wire)
  • Note that the ductile-to-brittle transition is low for their samples, 150-250C.
  • Samples made via arc-melting or WF + H2 CVD.

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ref: Prasad-2012.1 tags: tungsten microwire electrodes histology insulation failure sanchez microwire tungsten date: 06-27-2013 22:40 gmt revision:12 [11] [10] [9] [8] [7] [6] [head]

PMID-23010756[0] Comprehensive characterization and failure modes of tungsten microwire arrays in chronic neural implants.

  • c.f. [1]
  • microwire implant, durations that ranged from acute to up to 9 months in 25 rats.
  • First 2-3 weeks electrode impedance + recording quality fluctuated the most widely.
  • Electrode recording site deterioration continued for the long-term animals as insulation damage occurred and recording surface became more recessed over time.
  • Activated microglia were found near electrode tracts in all chronic animals.
    • High ferritin expression, intraparenchymal bleeding, microglial degeneration suggesting presence of excessive oxidative stress via Fenton chemistry.
      • Wikipedia: Free iron is toxic to cells as it acts as a catalyst in the formation of free radicals from reactive oxygen species via the Fenton Reaction.[11] Hence vertebrates use an elaborate set of protective mechanisms to bind iron in various tissue compartments.
  • Ferritin expression sometimes associated with blebbing / cytorrhexis. (in figures 7-8)
    • Interestingly, during the first few hours after implantation many microglial cells are undergoing cytoplasmic fragmentation (cytorrhexis) which indicates ongoing degeneration of these cells as their cytoplasm literally breaks apart. Cytorrhexis has been previously observed in the aged human brain where it becomes particular prominent in subjects with Alzheimer’s disease.
  • Could not discriminate abiotic (insulation, recording site size) and biotic (inflammatory response) causes of failure.
    • Microglial response not correlated with prolonged performance.
  • Tungsten TDT microwire arrays. 50um diameter, 10um polyimide insulation.
  • SEM imaging pre and prior implantation.
  • Antibodies marking microglia:
    • Iba1 marks all microglia.
    • ED1 stain against CD68 to identify active macrophages [80], but not necessarily all activated microglia since many activated cells are not engaged in phagocytosis and thus are ED1-negative.
    • Anti-ferritin staining to identify those microglia involved in the sequestration of free iron that may leak as a result of BBB compromize.
      • Issue: ferritin is expressed in all tissues ..
    • OX-6 to identify antigen-presenting MHC-II (immune) cells, e.g. microglia or blood-borne immune cells.
  • Found the immunohistoheamistry not terribly convincing.
    • Above, arrows show withdrawn electrode tips.
  • Working with the FDA to promote good laboratory practice (GLP) and good manufacturing practice (GMP). Can mention the same.
  • No evidence of infection in rats.
    • Not true in monkeys..

____References____

[0] Prasad A, Xue QS, Sankar V, Nishida T, Shaw G, Streit WJ, Sanchez JC, Comprehensive characterization and failure modes of tungsten microwire arrays in chronic neural implants.J Neural Eng 9:5, 056015 (2012 Oct)
[1] Freire MA, Morya E, Faber J, Santos JR, Guimaraes JS, Lemos NA, Sameshima K, Pereira A, Ribeiro S, Nicolelis MA, Comprehensive analysis of tissue preservation and recording quality from chronic multielectrode implants.PLoS One 6:11, e27554 (2011)

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ref: Hubel-1957.03 tags: Hubel original tungsten electrode date: 01-03-2012 23:46 gmt revision:3 [2] [1] [0] [head]

PMID-17793797[0] Tungsten Microelectrode for Recording from Single Units.

  • Advancement upon the micropipette.
  • Lacquer insulation.
  • Suggest that 5um tips or smaller are the best for single unit recording.
  • Steel becomes too fragile near the tip of a very sharp point (what about steel blades?)
  • Electropolishing: immerse a few milimeters in KNO 2 solution and apply 2-6V AC.
    • Such a result is explained by the fact that the meniscus height depends on the diameter of the wire, which decreases as the polishing proceeds.
  • 75M resistance (!!); 500k to 5M at 5-10kHz.
  • Note that he had been recording from at least 1959.

____References____

[0] Hubel DH, Tungsten Microelectrode for Recording from Single Units.Science 125:3247, 549-50 (1957 Mar 22)