SPARC: Soft silicone electrode net for modulating bladder function
Authors: Kumar Ritesh , Gopinath Chaitanya , Simpson Tyler , Weir David , Jantz Maria , Thiessen Alexander , McDonnall Danny , Gaunt Robert 
Published: April 2020

Bladder wall stimulation has been attempted for many decades to restore bladder function in people with spinal cord injury and other voiding dysfunctions. However, these efforts were limited by current spread to urethral structures, activation of the legs and co‐recruitment of other pelvic organs. Neural interfaces for the detrusor muscle itself face several challenges due to its unique structure and function. To directly modulate the bladder and urethra, we designed a stretchable electrode array that interfaces directly with the surface of these organs. With a stretchable electrode array that conforms to the bladder wall, we aim to create direct organ interface electrodes to stimulate and record from the bladder wall.

Acute experiments in isoflurane‐anesthetized cats (n=9, 8 males, 1 female) were performed to characterize the functional and electromechanical properties of this polymer electrode. Nerve cuffs were placed bilaterally on the hypogastric and pelvic nerves to record neural activity during bladder wall stimulation. Fine wire electromyography (EMG) electrodes were placed in gluteal muscle as well as the external anal and urethral sphincters to measure current spread. A pressure catheter was placed transurethrally to record pressure and infuse saline into the bladder. Elastic electrodes were placed on the dorsal, ventral, and both lateral aspects of the bladder. In an isovolumetric bladder state, each electrode was stimulated (at amplitude: 2–8 mA, frequency: 3 – 33 Hz, pulse width: 1ms) while recording bladder pressure and compound action potentials in the instrumented nerves. To determine the mechanism of action, pelvic and hypogastric nerves were transected sequentially while measuring bladder pressure.

We found that electrodes positioned near the bladder neck around the ureterovesical junction elicited the largest bladder contractions up to ~45 cmH2O while other locations such as the bladder dome generated significantly smaller contractions (~10 cmH2O). Bipolar stimulation on the bladder limited activation of the urethral sphincter and hind limbs through current spread compared to monopolar stimulation as shown by significant reduction in EMG activity with similar increases in bladder pressure. EMG recorded from the bladder wall had a directly proportional relation between frequency and volume thereby depicting detrusor muscle activity. Finally, we found that the passive mechanical effects of the silicone net around the bladder had a minimal impact (< 5 cmH2O) on bladder pressure. Following nerve transection, single electrode stimulation on the ureterovesical junction resulted in smaller pressure increases compared to before transection, whereas there was no change in the pressures evoked by multi‐electrode stimulation.

These soft silicone electrode nets can be used as a neural interface to generate bladder contractions in conditions where the bladder is underactive or atonic and enables continuous monitoring of detrusor EMG to monitor bladder state. Bladder wall stimulation acts through both direct‐efferent and reflex‐driven afferent mechanisms depending on stimulation location and charge.

Support or Funding Information

NIH SPARC OT2OD025297