Laser Microfabricated Polymer Microelectrodes for Intraspinal Microstimulation

• Author / Creator

  Roszko, David A.

• Intraspinal microstimulation (ISMS) is a neural prosthetic technique which can restore locomotor function in models of severe spinal cord injury (SCI). Historically, ISMS has been implemented with microwire electrodes or rigid multielectrodes, which suffer from limitations related to either functionality or biocompatibility. Microwire electrodes, although demonstrating chronic biocompatibility, are functionally limited in that they can only electrically stimulate one discrete location - at the deinsulated tip. Multielectrodes, although capable of stimulating multiple discrete sites along the device shank, are typically large and constructed from stiff materials which can increase tissue damage and exacerbate foreign body responses. A recent trend in neural interface research has focused on developing flexible multisite electrodes for the nervous system which can stimulate multiple targets while reducing foreign body responses caused by mechanical mismatch between the implanted device and the nervous system.
  In this research, a flexible polymer-substrate penetrating multielectrode for the spinal cord was developed as a way to improve the efficacy and biocompatibility of ISMS. Polymer multielectrodes were created from platinum-iridium foil and a polydimethylsiloxane-based substrate using laser microfabrication methods. Electrochemical properties of the laser-deinsulated multielectrode stimulating sites were assessed with standard electrochemical methods, including electrochemical impedance spectroscopy, cyclic voltammetry, and voltage transients, and were compared against microwire electrodes in phosphate buffered saline and in vivo in domestic pigs. Multielectrode mechanical properties were characterized through standard compression tests, in which the buckling force and theoretical Young’s modulus were compared against those of microwire electrodes. Lastly, multielectrode functionality was verified in vivo in a pig model of spinal cord injury by stimulating within the spinal cord and measuring evoked isometric joint torques and joint kinematics.
  Polymer multielectrodes were shown to be significantly more flexible than microwire electrodes, owing to their exceptionally flexible PDMS substrates. Multielectrode laser-roughened stimulating sites were shown to have higher charge storage capacities than microwire electrodes in phosphate buffered saline and higher charge injection limits than microwire electrodes in vivo. When stimulating within the pig spinal cord, polymer multielectrodes were capable of producing joint torques and kinematics similar to those previously generated by microwire electrodes. However, acute tissue damage from implanting the multielectrodes with rigid insertion aids generated significantly more acute tissue damage than the microwire electrodes - suggesting that other insertion aid methods should be explored. Overall, these results suggest that this new polymer multielectrode design may improve targeting, functionality and biointegration in models of spinal cord injury.

• Subjects / Keywords

  • spinal cord injury
  • intraspinal microstimulation
  • laser microfabrication
  • polymer microelectrode
  • neural prosthesis

• Graduation date

  Fall 2021

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-sf7d-x122

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.