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ref: -1977 tags: polyethylene surface treatment plasma electron irradiation mechanical testing saline seawater accelerated lifetime date: 04-15-2017 06:06 gmt revision:0 [head]

Enhancement of resistance of polyethylene to seawater-promoted degradation by surface modification

  • Polyethylene, when repeatedly stressed and exposed to seawater (e.g. ships' ropes), undergoes mechanical and chemical degradation.
  • Surface treatments of the polyethlyene can improve resistance to this degradation.
  • The author studied two methods of surface treatment:
    • Plasma (glow discharge, air) followed by diacid (adipic acid) or triisocyanate (DM100, = ?) co-polymerization
    • Electron irradiation with 500 kEV electrons.
  • Also mention CASING (crosslinking by activated species of inert gasses) as a popular method of surface treatment.
    • Diffuse-in crosslinkers is a third, popular these days ...
    • Others diffuse in at temperature e.g. a fatty acid - derived molecule, which is then bonded to e.g. heparin to reduce the thrombogenicity of a plastic.
  • Measured surface modifications via ATR IR (attenuated total reflectance, IR) and ESCA (aka XPS)
    • Expected results, carbonyl following the air glow discharge ...
  • Results:
    • Triisocyanate, ~ 6x improvement
    • diacid, ~ 50 x improvement.
    • electron irradiation, no apparent degradation!
      • Author's opinion that this is due to carbon-carbon crosslink leading to mechanical toughening (hmm, evidence?)
  • Quote: since the PE formulation studied here was low-weight, it was expected to lose crystallinity upon cyclic flexing; high density PE's have in fact been observed to become more crystalline with working.
    • Very interesting, kinda like copper. This could definitely be put to good use.
  • Low density polyethylene has greater chain branching and entanglement than high-density resins; when stressed the crystallites are diminished in total bulk, degrading tensile properties ... for high-density resins, mechanical working loosens up the structure enough to allow new crystallization to exceed stress-induced shrinkage of crystallites; hence, the crystallinity increases.

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ref: -0 tags: nanopore membrane nanostraws melosh surface adhesion intracellular date: 02-06-2017 23:34 gmt revision:0 [head]

PMID-22166016 Nanostraws for Direct Fluidic Intracellular Access

  1. Used track-etched polycarbonate membranes, which have controlled pore density & ID.
  2. Deposited alumina on the pores & external surfaces using ALD
  3. Then etched away the top alumina
  4. and finally used O2 RIE to etch away the polycarbonate.
  • Show that these nanopores have cytosolic access (via Fluor 488 - hydrazide membrane impermeant dye
  • Also used nanostraws to deliver Co+2 to quench GFP fluorescence.

PMID-24710350, Quantification of nanowire penetration into living cells.

  • We discover that penetration is a rare event: 7.1±2.7% of the nanostraws penetrate the cell to provide cytosolic access for an extended period for an average of 10.7±5.8 penetrations per cell.
  • Using time-resolved delivery, the kinetics of the first penetration event are shown to be adhesion dependent and coincident with recruitment of focal adhesion-associated proteins.
    • Hours for unmodified, 5 minutes for adhesion-promoting surface.
  • Chinese hamster oviary cells expressing GFP, Co+2 quenching, EDTA chelation.
  • To modulate cell adhesion, nanostraw substrates were incubated in 10 μg ml−1 fibronectin, a well-characterized cell adhesion molecule, in addition to the standard polyornithine coating.

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ref: -0 tags: polyimide polyamide basic reduction salt surface modification date: 02-27-2015 19:45 gmt revision:0 [head]

Kinetics of Alkaline Hydrolysis of a Polyimide Surface

  • The alkaline hydrolysis of a polyimide (PMDA-ODA) surface was studied as a function of time, temperature and hydroxide ion concentration.
  • Quantification of the number of carboxylic acid groups formed on the modified polyimide surface was accomplished by analysis of data from contact angle titration experiments.
  • Using a large excess of base, pseudo-first-order kinetics were found, yielding kobs ≈ 0.1−0.9 min-1 for conversion of polyimide to poly(amic acid) depending on [OH-].
  • From the dependence of kobs on [OH-], a rate equation is proposed.
  • Conversion of the polyimide surface to one of poly(amic acid) was found to reach a limiting value with a formation constant, K, in the range 2−10 L·mol-1.

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ref: -0 tags: polyimide adhesion oxygen nitrogen plasma surface energy date: 03-10-2014 22:33 gmt revision:0 [head]

Adhesion Properties of Electroless-Plated Cu Layers on Polyimide Treated by Inductively Coupled Plasmas

  • O2 then N2/H2 ICP treatment of polyimide surfaces dramatically lowers the surface energy (as measured by contact angle), and increases the adhesion of palladium-catalyzed electroless copper.
  • Particularly, C-N bonds are increased as revealed by XPS.
  • No peel-strength measurements given.

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ref: -0 tags: polyimide adhesion silver surface treatment adhesion delamination date: 10-04-2013 01:30 gmt revision:8 [7] [6] [5] [4] [3] [2] [head]

Improved polyimide/metal adhesion by chemical modification approaches

  • Suggest fuming sulfuric acid (H2S04) + Ag2SO4 for 30s as the most effective treatment.
  • 1 minute in 1M KOH also effective.
  • Silver was magnetron-sputtered on; peel test performed with tape.

IEEE-4936772 (pdf) Studies of adhesion of metal films to polyimide

  • Suggest Ar / O2 plasma treatment of surface to increase Cr/Cu adhesion (mechanical effect?)
  • Used two different polyimides: one derived from (BPDA‐PDA) polyamic acid, and pyromellitic dianhydride‐4,4’‐oxydianiline (PMDA‐ODA).

IEEE-670747 (pdf) Adhesion evaluation of adhesiveless metal/polyimide substrate for MCM and high density packaging

  • Adhesion of Cr / polyimide interface is degraded significantly upon exposure to high temperature and humidity environment due to the hydrolysis of polyimide.
  • There is also some worry of Cu diffusion into the polyimide.
  • All used a Cr tie layer, 200A thick (20nm).
  • Deposited photoresist, electroplated copper, then etched to define pattern.
  • Testing performed at 121C 100% RH, +15psi. (tough!)

On polyimide-polyimide interlayer adhesion: Diffusion and self-adhesion of the polyimide PMDA-ODA (1987)

  • Diffusion occurred during the curing process of the second layer and was controlled by the cure schedule.
  • It was found that a large diffusion distance, at least 200 nm, was required to obtain a bond whose strength was equal to that of bulk material.
  • Good protocol:
    • Dry first layer at 80C for 30 minutes.
    • 150C (or lower?) bake of first layer. "as the polyamic acid imidizes (and the solvent is lost) its diffusive mobility decreases rapidly; very little diffusion occurs after the first few minutes of the second bake.
    • Spin coat second layer.
    • 400C second bake.
  • Ductility is increased for polyimide that has experienced a series of increasing cure temperatures.
  • In this context it is worth noting that the contour length of a PMDA-ODA of 30,000 molecular weight is about 130nm, a value very similar to the diffusion distances measured when T1 (first layer bake) was 150C.

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ref: Skousen-2011.01 tags: electrodes immune response Tresco Wise Michigan histology GFAP atrocyte surface area foreign body response date: 01-25-2013 01:44 gmt revision:5 [4] [3] [2] [1] [0] [head]

PMID-21867802[0] Reducing surface area while maintaining implant penetrating profile lowers the brain foreign body response to chronically implanted planar silicon microelectrode arrays.

  • We studied the chronic brain foreign body response to planar solid silicon microelectrode arrays and planar lattice arrays with identical penetrating profiles but with reduced surface area in rats after an 8-week indwelling period.
  • Using quantitative immunohistochemistry, we found that presenting less surface area after equivalent iatrogenic injury is accompanied by significantly less
    • persistent macrophage activation,
    • decreased blood brain barrier leakiness,
    • and reduced neuronal cell loss.
  • Could be a factor of micromotion, too -- the lattice array has more anchoring points (?)
  • They propose it's a factor of TNF- α concentration around the implants. This, and other proinflammatory and cytoxic cytokines, is released by macrophages.
  • "Recent studies from our lab have described disruption of BBB integrity, indicated by the presence of autologous IgG in the brain parenchyma, surrounding both microwire and planar silicon recording devices ([1][2]. Under normal conditions, autologous IgG is excluded from the brain parenchyma (Azzi et al., 1990; Seitz et al., 1985) but has been observed following BBB disruption (Aihara et al., 1994).
    • E.g. the presence of IgG proves that the BBB was compromised.
      • Less so with the lattice implants.
  • Previous work from our lab using single microwires and single shaft, planar silicon microelectrode arrays indicated that the spatial distribution of GFAP does not increase with time over the indwelling period and did not support the “increase in astrogliosis over time hypothesis” as a dominant or general biologically related failure mechanism for this type of microelectrode recording device {1197}.

____References____

[0] Skousen JL, Merriam SM, Srivannavit O, Perlin G, Wise KD, Tresco PA, Reducing surface area while maintaining implant penetrating profile lowers the brain foreign body response to chronically implanted planar silicon microelectrode arrays.Prog Brain Res 194no Issue 167-80 (2011)
[1] Winslow BD, Christensen MB, Yang WK, Solzbacher F, Tresco PA, A comparison of the tissue response to chronically implanted Parylene-C-coated and uncoated planar silicon microelectrode arrays in rat cortex.Biomaterials 31:35, 9163-72 (2010 Dec)
[2] Winslow BD, Tresco PA, Quantitative analysis of the tissue response to chronically implanted microwire electrodes in rat cortex.Biomaterials 31:7, 1558-67 (2010 Mar)

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ref: Zhang-2009.02 tags: localized surface plasmon resonance nanoparticle neural recording innovative date: 01-15-2012 23:00 gmt revision:4 [3] [2] [1] [0] [head]

PMID-19199762[0] Optical Detection of Brain Cell Activity Using Plasmonic Gold Nanoparticles

  • Used 140 nm diameter, 40 nm thick gold disc nanoparticles set in a 400nm array, illuminated by 850nm diode laser light.
    • From my reading, it seems that the diameter of these nanoparticles is important, but the grid spacing is not.
  • These nanoparticles strongly scatter light, and the degree of scattering is dependent on the local index of refraction + electric field.
  • The change in scattering due to applied electric field is very small, though - ~ 3e-6 1/V in the air-capacitor setup, ~1e-3 in solution when stimluated by cultured hippocampal neurons.
  • Noteably, nanoparticles are not diffraction limited - their measurement resolution is proportional to their size. Compare with voltage-sensitive dyes, which have a similar measurement signal-to-noise ratio, are diffraction limited, may be toxic, and may photobleach.

____References____

[0] Zhang J, Atay T, Nurmikko AV, Optical detection of brain cell activity using plasmonic gold nanoparticles.Nano Lett 9:2, 519-24 (2009 Feb)

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ref: Maschietto-2009.07 tags: recording ASIC surface recording date: 01-15-2012 22:06 gmt revision:1 [0] [head]

IEEE-5230909 (pdf) A High Resolution Bi-Directional Communication through a Brain-Chip Interface

  • 1000 channels, 10um pitch if thin-film transistors.
  • innovative!
  • EOSFET - electrolyte oxide semiconductor field effect transistor.

____References____

Maschietto, M. and Mahmud, M. and Stefano, G. and Vassanelli, S. Advanced Technologies for Enhanced Quality of Life, 2009. AT-EQUAL '09. 32 -35 (2009)

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ref: Merletti-2009.02 tags: surface EMG multielectrode recording technology italy date: 01-03-2012 01:07 gmt revision:2 [1] [0] [head]

PMID-19042063[0] Technology and instrumentation for detection and conditioning of the surface electromyographic signal: state of the art

  • good background & review of surface EMG (sEMG) - noise levels, electrodes, electronics. eg. Instrumentation amplifiers with an input resistance < 100MOhm are not recommended, and the lower the input capacitance, the better: the impedance of a 10pf capacitor at 100hz is 160MOhm.
  • Low and balanced input impedances are required to reduce asymmetric filtering of common-mode power-line noise.

____References____

[0] Merletti R, Botter A, Troiano A, Merlo E, Minetto MA, Technology and instrumentation for detection and conditioning of the surface electromyographic signal: state of the art.Clin Biomech (Bristol, Avon) 24:2, 122-34 (2009 Feb)