The Injectrode – a truly injectable electrode for dorsal root ganglion stimulation to treat pain

Study Purpose: 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.

Data Collection: 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.

Primary Conclusion: The rate of recruitment was similar between the Injectrodes and stainless steel electrode and decreased with wider pulse widths. 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.

Curator's Notes

Experimental Design: Acute experiments were performed in four adult male cats (4.38–7.55 kg) under isoflurane anesthesia (2-2.5%) following induction with either ketamine/acepromazine or dexdomitor. The L6 and L7 dorsal root ganglia (DRG) were exposed via partial laminectomy or burr hole in the vertebral laminae for electrode placement. Both stainless steel electrodes and the Injectrode were tested, with a stimulation ground electrode placed between the skin and lumbodorsal fascia for monopolar stimulation. Monopolar stimulation was delivered at 58 Hz using biphasic, cathodic-leading pulses with pulse widths of 80, 150, or 300 μs per phase. Recruitment curves were constructed by varying stimulation amplitude from below sensory threshold to motor threshold in randomized steps, with 600 pulses delivered at each amplitude. Electroneurogram signals were recorded from the sciatic, tibial, and common peroneal nerves using spiral nerve cuffs connected to a Grapevine Neural Interface Processor, filtered (0.1 Hz high pass, 7.5 kHz low pass), and digitized at 30 kS/s.

Completeness: This dataset is complete.

Subjects & Samples: Male (n=4) adult domestic cats were used in this study.

Primary vs derivative data: The primary data is organized into folders by subject ID, with each subject folder containing subfolders for different performance sessions. Within each performance subfolder, raw files are stored in NS5/NEV format from electrode recordings of the testing sessions (perf-). The primary data includes electrochemical impedance spectroscopy (EIS) measurements where frequency values ranging from 1 to 100,000 Hz at eight points per decade and a peak-to-peak voltage of 25 mV were tested. The derivative data is housed in a separate folder containing MATLAB figure plots and PNG photos of graphed data. These derivative files were generated through processing of the primary data and display the analyzed results of antidromic evoked compound action potentials, conduction velocities, and fiber recruitment patterns collected during the experiments.

Important Information: A detailed video of Injectrode implantation is provided; .mp4 can be found in the protocol folder.

Code Availability: To use the files and data from the dataset, first open the RippleNeuroshareDemo1 code file on MATLAB which explains and provides a demo on how to open and edit the data in the .nev and .ns5 files. Additional information and code documentation can be found on Neuroshare MATLAB API website.