ABSTRACT
Objective The goal of this work was to compare afferent fiber recruitment by dorsal root ganglion (DRG) stimulation using an injectable polymer electrode (Injectrode®) and a more traditional cylindrical metal electrode.
Approach We exposed the L6 and L7 DRG in four cats via a partial laminectomy or burr hole. We stimulated the DRG using an Injectrode or a stainless steel electrode using biphasic pulses at three different pulse widths (80, 150, 300 μs) and pulse amplitudes spanning the range used for clinical DRG stimulation. We recorded antidromic evoked compound action potentials (ECAPs) in the sciatic, tibial, and common peroneal nerves using nerve cuffs. We calculated the conduction velocity of the ECAPs and determined the charge-thresholds and recruitment rates for ECAPs from Aα, Aβ, and Aδ fibers. We also performed electrochemical impedance spectroscopy measurements for both electrode types.
Main Results The ECAP thresholds for the Injectrode did not differ from the stainless steel electrode across all primary afferents (Aα, Aβ, Aδ) and pulse widths; charge-thresholds increased with wider pulse widths. Thresholds for generating ECAPs from Aβ fibers were 100.0 ± 32.3 nC using the stainless steel electrode, and 90.9 ± 42.9 nC using the Injectrode. The ECAP thresholds from the Injectrode were consistent over several hours of stimulation. The rate of recruitment was similar between the Injectrodes and stainless steel electrode and decreased with wider pulse widths.
Significance The Injectrode can effectively excite primary afferents when used for DRG stimulation within the range of parameters used for clinical DRG stimulation. The Injectrode can be implanted through minimally invasive techniques while achieving similar neural activation to conventional electrodes, making it an excellent candidate for future DRG stimulation and neuroprosthetic applications.
Competing Interest Statement
MF, AJS, and KAL are co-founders of Neuronoff, Inc. and co-inventors on intellectual property relating to the Injectrode. SN, DJW, and JKT are shareholders for Neuronoff Inc. AJS, KAL, MF, and SN are employees at Neuronoff, Inc. KAL is a scientific board member and has stock interests in NeuroOne Medical Inc. KAL is also a paid member of the scientific advisory board of Cala Health, Blackfynn, and Battelle, and a paid consultant for Galvani. DJW is a scientific board member for NeuroOne Medical Inc. and a paid consultant for Innervace. JKT is a paid consultant for Iota Biosciences. SFL holds stock options, serves on the scientific advisory board, and has received research support from Presidio Medical Inc., and is a shareholder at Hologram Consultants, LLC. SFL is also a member of the scientific advisory board for Abbott Neuromodulation, and receives research support from Medtronic, Inc. None of these associations outside those to Neuronoff, Inc. are directly relevant to the work presented in this manuscript.
Footnotes
Updated with minor revisions.