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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: reactive oxygen accelerated aging neural implants date: 10-07-2015 18:45 gmt revision:1 [0] [head]

PMID-25627426 Rapid evaluation of the durability of cortical neural implants using accelerated aging with reactive oxygen species.

  • Takmakov P1, Ruda K, Scott Phillips K, Isayeva IS, Krauthamer V, Welle CG.
  • TDT W / PI implants completely failed (W etched and PI completely flaked off) after 1 week in 87C H2O2 / PBS solution. Not surprising.
    • In the Au plated W, the Au remained, the PI flaked off, while thin fragile gold tubes were left. Interesting.
  • Pt/Ii + Parylene-C microprobes seemed to fare better; one was unaffected, others experienced a drop in impedance.
  • NeuralNexus (Si3N4 insulated, probably, plus Ir recording pads) showed no change in H2O2 RAA, strong impedance drop (thicker oxide layer?)
  • Same for blackrock / utah probe (Parylene-C), though there the parylene peeled from the Si substrate a bit.