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ref: Kozai-2009.11 tags: electrodes insertion Kozai flexible polymer momolayer date: 12-28-2017 02:59 gmt revision:12 [11] [10] [9] [8] [7] [6] [head]

PMID-19666051[0] Insertion shuttle with carboxyl terminated self-assembled monolayer coatings for implanting flexible polymer neural probes in the brain.

  • This study investigated the use of an electronegative (hydrophillic) self-assembled monolayer (SAM) as a coating on a stiff insertion shuttle to carry a polymer probe into the cerebral cortex, and then the detachment of the shuttle from the probe by altering the shuttle's hydrophobicity.
    • Used 11-mercaptoundecanoic acid.
    • Cr/Au (of course) evaporated on 15um thick Si shuttle.
    • SAM attracts water once inserted, causing the hydrophobic polymer to move away.
      • Why not make the polymer hydrophillic?
      • Is this just soap?
  • Used agarose brain model.
  • Good list of references for the justification of soft electrodes, and researched means for addressing this, mostly usnig polymer stiffeners.
    • "Computer models and experimental studies of the probe–tissue interface suggest that flexible and soft probes that approach the brain’s bulk material characteristics may help to minimize micromotion between the probe and surrounding tissue ({737}; {1203}; {1102}; {1200}; LaPlaca et al., 2005; {1216}; Neary et al., 2003 PMID-12657694; {1198})"
  • "However, polymer probes stick to metallic and silicon surfaces through hydrophobic interactions, causing the polymer probe to be carried out of the brain when the insertion shuttle is removed. The solution is to use a highly hydrophillic, electronegative, self-assembled monolayer coating on the shuttle.
  • Biran et al 2005 suggests that incremental damage due to stab wounds from the shuttle (needle) should be minor.
  • Probes: 12.5 um thick, 196 um wide, and 1.2cm long, polymide substrate and custom designed lithographed PDMS probes.
  • Polymer probes were inserted deep - 8.5 mm.
  • PDMS probes inserted with non-coated insertion shuttle resulted in explantation of the PDMS probe.

____References____

[0] Kozai TD, Kipke DR, Insertion shuttle with carboxyl terminated self-assembled monolayer coatings for implanting flexible polymer neural probes in the brain.J Neurosci Methods 184:2, 199-205 (2009 Nov 15)

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ref: -0 tags: lieber mesh electronics SU-8 recording electrodes flexible polymer glass capillary date: 12-22-2017 00:14 gmt revision:0 [head]

PMID-29109247 Highly scalable multichannel mesh electronics for stable chronic brain electrophysiology

  • Key change was the addition of multiple conductor traces per longitudinal mesh line; this allows them to get 64 or 128 channels per mesh without a dramatic increase in modulus.
  • The latitudinal / diagonal lines still displace tissue ...
  • And the injection mechanism, glass pipette, 650um OD, 400um ID, is pretty large, even for 128 channels.
  • Use carbon nanotube ink, custom CNC printer, to connect to FPC.
    • Pretty impressive that they can manipulate ~800nm thick Su-8 film intraop and have it work well!

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ref: -0 tags: review neural recording penn state extensive biopolymers date: 02-06-2017 23:09 gmt revision:0 [head]

PMID-24677434 A Review of Organic and Inorganic Biomaterials for Neural Interfaces

  • Not necessarily insightful, but certainly exhaustive review of all the various problems and strategies for neural interfacing.
  • Some emphasis on graphene, conductive polymers, and biological surface treatments for reducing FBR.
  • Cites 467 articles!

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ref: -0 tags: graphene polyimide polymerization date: 01-22-2017 05:20 gmt revision:3 [2] [1] [0] [head]

Preparation and properties of graphene oxide/polyimide composite films with low dielectric constant and ultrahigh strength via in situpolymerization

  • The GO/PI composite films provide ultrahigh tensile strength (up to 844 MPa) and Young's modulus (20.5 GPa).
    • Almost 10x increase in tensile strength!
    • And even larger increase in modulus.
  • Also, you can reduce graphene / graphite oxide with an infrared laser: http://pubs.acs.org/doi/abs/10.1021/nn204200w

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ref: -0 tags: LCP polymer Zeus tensile modulus date: 11-11-2016 20:39 gmt revision:0 [head]

https://www.zeusinc.com/materials/lcp-liquid-crystal-polymer

  • UTS 1.0 GPa; 80 MPa Youngs modulus.
  • No data on moisture uptake or molecular structure.

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ref: -0 tags: PEDOT electropolymerization electroplating gold TFB borate counterion acetonitrile date: 10-18-2016 07:49 gmt revision:3 [2] [1] [0] [head]

Electrochemical and Optical Properties of the Poly(3,4-ethylenedioxythiophene) Film Electropolymerized in an Aqueous Sodium Dodecyl Sulfate and Lithium Tetrafluoroborate Medium

  • EDOT has a higher oxidation potential than water, which makes polymers electropolymerized from water "poorly defined".
  • Addition of SDS lowers the oxidation potential to 0.76V, below that of EDOT in acetonitrile at 1.1V.
  • " The potential was first switched from open circuit potential to 0.5 V for 100 s before polarizing the electrode to the desired potential. This initial step was to allow double-layer charging of the Au electrode|solution interface, which minimizes the distortion of the polymerization current transient by double-layer capacitance charging.17,18 "
    • Huh, interesting.
  • Plated at 0.82 - 0.84V, 0.03M EDOT conc.
  • 0.1M LiBF4 anion / electrolyte; 0.07M SDS sufactant.
    • This SDS is incorporated into the film, and affects redox reactions as shown in the cyclic voltammagram (fig 4)
      • Doping level 0.36
    • BF4-, in comparison, can be driven out of the film.

Improvement of the Electrosynthesis and Physicochemical Properties of Poly(3,4-ethylenedioxythiophene) Using a Sodium Dodecyl Sulfate Micellar Aqueous Medium

  • "The oxidation potential of thiopene = 1.8V; water = 1.23V.
  • Claim: "The polymer films prepared in micellar medium [SDS] are more stable than those obtained in organic solution as demonstrated by the fact that, when submitted to a great number of redox cycles (n ≈ 50), there is no significant loss of their electroactivity (<10%). These electrochemical properties are accompanied by color changes of the film which turns from blue-black to red-purple upon reduction."
  • Estimate that there is about 21% DS- anions in the PEDOT - SDS films.
    • Cl - was at ~ 7%.
  • I'm still not sure about incorporating soap into the electroplating solution.. !

Electrochemical Synthesis of Poly(3,4-ethylenedioxythiophene) on Steel Electrodes: Properties and Characterization

  • 0.01M EDOT and 0.1M LiClO4 in acetonitrile.
  • Claim excellent adhesion & film properties to 316 SS.
  • Oxidation / electrodeposition at 1.20V; voltages higher than 1.7V resulted in flaky films.

PMID-20715789 Investigation of near ohmic behavior for poly(3,4-ethylenedioxythiophene): a model consistent with systematic variations in polymerization conditions.

  • Again use acetonitrile.
  • 1.3V vs Ag/AgCl electrode.
  • Perchlorate and tetraflouroborate both seemed the best counterions (figure 4).
  • Figure 5: Film was difficult to remove from surface.
    • They did use a polycrystaline Au layer:
    • "The plating process was allowed to run for 1 min (until approximately 100 mC had passed) at a constant potential of 0.3 V versus Ag/AgCl in 50 mM HAuCl4 prepared in 0.1 M NaCl."
  • Claim that the counterions are trapped; not in agreement with the SDS study above.
  • "Conditions for the consistent production of conducting polymer films employing potentiostatic deposition at 1.3 V for 60-90 s have been determined. The optimal concentration of the monomer is 0.0125 M, and that of the counterion is 0.05 M. "

PMID-24576579 '''Improving the performance of poly(3,4-ethylenedioxythiophene) for brain–machine interface applications"

  • Show that TFB (BF4-) is a suitable counterion for EDOT electropolymerization.
  • Comparison is between PEDOT:TFB deposited in an anhydrous acetronitrile solution, and PEDOT:PSS deposited in an aqueous solution.
    • Presumably the PSS brings the EDOT into solution (??).
  • figure 3 is compelling, but long-term, electrodes are not that much better than Au!
    • Maybe we should just palate with that.

PEDOT-modified integrated microelectrodes for the detection of ascorbic acid, dopamine and uric acid

  • Direct comparison of acetonitrile and water solvents for electropolymerization of EDOT.
  • "PEDOT adhesion is best on gold surface due to the strong interactions between gold and sulphur atoms.
  • images/1353_2.pdf
    • Au plating is essential!

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ref: -0 tags: adhesion polymer metal FTIR epoxy eponol paint date: 05-01-2015 19:20 gmt revision:0 [head]

Degradation of polymer/substrate interfaces – an attenuated total reflection Fourier transform infrared spectroscopy approach

  • Suggests why eponol is used as an additive to paint.
  • In this thesis, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy has been used to detect changes at the interfaces between poly (vinyl butyral-co-vinyl alcohol-co-vinyl acetate) (PVB) and ZnSe upon exposure to ozone, humidity and UV-B light.
  • Also, the response of PVB-aluminum interfaces to liquid water has been studied and compared with the same for eponol (epoxy resin, diglycidyl ether of bisphenol A)-aluminum interfaces.
  • In the presence of ozone, humidity and UV-B radiation, an increase in carbonyl group intensity was observed at the PVB-ZnSe interface indicating structural degradation of the polymer near the interface. However, such changes were not observed when PVB coated ZnSe samples were exposed to moisture and UV-B light in the absence of ozone showing that ozone is responsible for the observed structural deterioration. Liquid water uptake kinetics for the degraded PVB monitored using ATR-FTIR indicated a degradation of the physical structural organization of the polymer film.
  • Exposure of PVB coated aluminum thin film to de-ionized water showed water incorporation at the interface. There were evidences for polymer swelling, delamination and corrosion of the aluminum film under the polymer layer.
    • On the contrary, delamination/swelling of the polymer was not observed at the eponol-aluminum interface, although water was still found to be incorporated at the interface. Al-O species were also observed to form beneath the polymer layer.
    • A decrease of the C-H intensities was detected at the PVB-aluminum interface during the water uptake of the polymer, whereas an increase of the C-H intensities was observed for the eponol polymer under these conditions.
    • This is assigned to rearrangement of the macromolecular polymer chains upon interaction with water.

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ref: -0 tags: kevlar electrodes flexible polymer 12um McNaughton Utah date: 10-11-2014 00:19 gmt revision:0 [head]

PMID-8982987 Metallized polymer fibers as leadwires and intrafascicular microelectrodes

  • McNaughton TG1, Horch KW.
  • Ti/W, Au, Pt metalization via sputtering.
  • 12um core diamater.
  • demonstrate 8 month reliability.
  • 1um dipped silicone elastomer insulation.
  • note difficulty in manufactuing the fibers. No kidding!
  • Tensile strength the same as a 25um Pt-Ir wire, 90x more flexible.

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ref: -0 tags: shape memory polymers neural interface thiolene date: 12-06-2013 22:55 gmt revision:0 [head]

PMID-23852172 A comparison of polymer substrates for photolithographic processing of flexible bioelectronics

  • Describe the deployment of shape-memory polymers for a neural interface
    • Thiol-ene/acrrylate network (see figures)
    • Noble metals react strongly to the thiols, yielding good adhesion.
  • Cr/Au thin films.
  • Devices change modulus as they absorb water; clever!
  • Transfer by polymerization patterning of electrodes (rather than direct sputtering).
    • This + thiol adhesion still might not be sufficient to prevent micro-cracks.
  • "Neural interfaces fabricated on thiol-ene/acrylate substrates demonstrate long-term fidelity through both in vitro impedance spectroscopy and the recording of driven local field potentials for 8 weeks in the auditory cortex of laboratory rats. "
  • Impedance decreases from 1M @ 1kHz to ~ 100k over the course of 8 weeks. Is this acceptable? Seems like the insulator is degrading (increased capacitance; they do not show phase of impedance)
  • PBS uptake @ 37C:
    • PI seems to have substantial PBS uptake -- 2%
    • PDMS the lowest -- 0.22%
    • PEN (polyethelene napathalate) -- 0.36%
    • Thiol-ene/acrylate 2.19%
  • Big problem is that during photolithographic processing all the shape-memory polymers go through Tg, and become soft/rubbery, making thin metal film adhesion difficult.
    • Wonder if you could pattern more flexible materials, e.g. carbon nanotubes (?)
  • Good paper, many useful references!

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ref: Sanders-2000.1 tags: polymer fiber immune reaction biocompatibility rats polycaprolactone recording electrodes histology MEA date: 01-28-2013 00:01 gmt revision:11 [10] [9] [8] [7] [6] [5] [head]

PMID-10906696[0] Tissue response to single-polymer fibers of varying diameters: evaluation of fibrous encapsulation and macrophage density.

  • Fibers smaller than 6μm show reduced immune response.
    • Fibers implanted in the subcutaneous dorsum (below the skin in the back of rats).
    • Polypropylene. (like rope).
    • Wish the result extended to small beads & small electrodes. 7μm is tiny, but possible with insulated Au wires.
      • Beads: try PMID-1913150 -- shows that the 600um - 50um beads ('microspheres') are well tolerated.
      • Also {750}.
  • Macrophage density in tissue with fiber diameters 2.1-5.9um comparable to that of unoperated contralateral control.

"

fiber diametercapsule thickness
2.1-5.90.6
6.5-10.611.7
11.1-15.820.3
16.7-26.725.5

____References____

[0] Sanders JE, Stiles CE, Hayes CL, Tissue response to single-polymer fibers of varying diameters: evaluation of fibrous encapsulation and macrophage density.J Biomed Mater Res 52:1, 231-7 (2000 Oct)

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ref: Lewitus-2011.08 tags: dissolving polymer electrodes histology degrading date: 01-25-2013 01:31 gmt revision:2 [1] [0] [head]

PMID-21609850[0] The fate of ultrafast degrading polymeric implants in the brain.

  • Tyrosene-derived terpolymer (protein?) dissolves within hours & was re-absorbed.
  • Second terpolymer degrades quickly but is not resorbed.
    • This type resulted in continuous glial activation and loss of neural tissue compared to first.
  • Makes sense, not unexpected.

____References____

[0] Lewitus DY, Smith KL, Shain W, Bolikal D, Kohn J, The fate of ultrafast degrading polymeric implants in the brain.Biomaterials 32:24, 5543-50 (2011 Aug)

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ref: -0 tags: flexible polymer electrode recording polypyrrole Bizzi date: 01-25-2013 00:39 gmt revision:0 [head]

PMID-19164034 Cortical recording with polypyrrole microwire electrodes.

  • http://web.mit.edu/bcs/bizzilab/publications/bae2008.pdf
  • Electropolymerization of PPy on a glassy carbon electrode in solution.
  • Polypyrrole microwires were prepared by mounting a PPy film perpendicular to the stage of a cryo-microtome and slicing it in 20um sections.
  • Electrode mounted inside a glass capillary tube.
  • Impedance: 1e5 @ 1kHz.

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ref: -0 tags: flexible polymer neural probes compliant MIT EPFL 2008 date: 12-22-2012 01:28 gmt revision:0 [head]

Demonstration of cortical recording using novel flexible polymer neural probes

  • Two layer platinum process minimizes probe size -- nice. Might be useful for our purposes.
  • used electrochemical etching to release the lithographically patterned devices from the sacrificial aluminum layer.
  • Impedance looks pretty high -- 500k at 1kHz.
  • They talk about PCA as though it's unusual to them (?)
  • Histology uncontrolled and un-quantitiative.