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ref: Harris-2011.12 tags: mechanically adaptive electrodes implants case western dissolving flexible histology Harris date: 01-25-2013 01:39 gmt revision:5 [4] [3] [2] [1] [0] [head]

PMID-22049097[0] Mechanically adaptive intracortical implants improve the proximity of neuronal cell bodies.

  • See also [1]
  • Initial tensile modulus of 5GPa dropped to 12MPa. (almost 500-fold!)
    • Their polymer nanocomposite (NC) still swells 65-70% (with water?)
    • Implant size 100 x 200um.
  • Controlled with tungsten of identical size and coating.
  • Tethered to skull.
  • Interesting:
    • The neuronal nuclei density within 100 ┬Ám of the device at four weeks post-implantation was greater for the compliant nanocomposite compared to the stiff wire.
    • At eight weeks post-implantation, the neuronal nuclei density around the nanocomposite was maintained, but the density around the wire recovered to match that of the nanocomposite.
    • Hypothesis, in discussion: softer implants are affecting the time-course of the response rather that final results
  • The glial scar response to the compliant nanocomposite was less vigorous than it was to the stiffer wire
  • Cultured astrocytes have been shown to respond to mechanical stimuli via calcium signaling (Ostrow and Sachs, 2005).
  • Substrate stiffness is also known to shift cell differentiation in mesenchymal stem cells to be neurogenic, myogenic, or osteogenic (Engler et al., 2006).
  • In vivo studies which focus on the effects of electrode tethering have shown that untethered implants reduce the extent of the glial scar (Biran et al., 2007; Kim et al., 2004; Subbaroyan, 2007)
  • Parylene, polymide, and PDMS still each have moduli 6 orders of mangitude larger than that of the brain.
  • In some of their plots, immune response is higher around the nanocomposites!
    • Could be that their implant is still too large / stiff?
  • Note that recent research shows that vitemin may have neuroprotective effects --
    • Research has linked vimentin expression to rapid neurite extension in response to damage (Levin et al., 2009)
    • NG2+ cells that express vimentin have been proposed to support repair of central nervous system (CNS) damage, and stabilize axons in response to dieback from ED1+ cells (Alonso, 2005; Nishiyama, 2007; Busch et al., 2010)
  • Prior work (Frampton et al., 2010 PMID-20336824[2]) hypothesizes that a more compact GFAP response increases the impedance of an electrode which may decrease the quality of electrode recordings.

____References____

[0] Harris JP, Capadona JR, Miller RH, Healy BC, Shanmuganathan K, Rowan SJ, Weder C, Tyler DJ, Mechanically adaptive intracortical implants improve the proximity of neuronal cell bodies.J Neural Eng 8:6, 066011 (2011 Dec)
[1] Harris JP, Hess AE, Rowan SJ, Weder C, Zorman CA, Tyler DJ, Capadona JR, In vivo deployment of mechanically adaptive nanocomposites for intracortical microelectrodes.J Neural Eng 8:4, 046010 (2011 Aug)
[2] Frampton JP, Hynd MR, Shuler ML, Shain W, Effects of glial cells on electrode impedance recorded from neuralprosthetic devices in vitro.Ann Biomed Eng 38:3, 1031-47 (2010 Mar)