(630.1) Soft silicone-based neural interface to modulate bladder function: chronic studies in awake behaving cats

Poster Board Number: E712

Ritesh Kumar (University of Pittsburgh), Chaitanya Gopinath (University of Pittsburgh), Tyler Simpson (University of Pittsburgh), David Weir (University of Pittsburgh), Alexander Thiessen (Ripple LLC), Danny McDonnall (Ripple LLC), Robert Gaunt (University of Pittsburgh)

Direct bladder wall stimulation has been attempted for decades to restore bladder function in people with spinal cord injury and other voiding dysfunctions. However, these efforts were limited by co-activation of the urethra, legs and other pelvic organs at stimulus intensities that evoked bladder contractions. Neural interfaces for the detrusor muscle itself face several challenges due to its structure and the volume changes it undergoes in normal function. We designed a stretchable silicone net that can be placed around the bladder body to anchor a soft electrode array that interfaces directly with the base of bladder to generate bladder contractions.

We created implantable versions of the electrode nets and tested them in chronic experiments. We implanted 5 healthy cats (4 females, 1 male) and tested them with and without anesthesia for 2-3 months. A pressure catheter was implanted into the bladder to control volume and measure pressure.

Bladder wall stimulation through various electrode configurations (monopolar, bipolar), temporal patterns (single electrode, sequential stimulation of multiple electrodes) and stimulus intensities were able to generate complete bladder emptying. In behaving cats, bladder wall stimulation at many different stimulus intensities elicited efficient voiding at physiological bladder pressures (med: 41, IQR: 27-60 cmH2O). However, there was little relationship (rlt;0.28) between stimulation amplitude and bladder pressure itself. Rather, stimulation amplitude had an effect on the time between stimulation onset and bladder contraction onset. At low stimulation amplitudes, there was a longer time between stimulation onset and voiding (med: 35s, IQR: 13.5-68.2s) than occurred at higher amplitudes, which evoked more rapid voiding (med: 23s, IQR: 10-45s). This contrasts with anesthetized tests, where stimulation at 3 ± 2 mA evoked increases in bladder pressure up to 35 cmH2O. These results suggest that stimulation of the bladder wall recruits sensory pathways leading to an urge to void, but that can be suppressed by the animals. For most of the duration of the implants, stimulation evoked functional voiding with consistent electrical stimulation thresholds. However, after several months there was a failure of an implanted bond that limited the overall duration of the implants.

Chronic experiments demonstrate that these electrode nets can be used as a neural interface to generate or initiate comfortable, complete bladder emptying in awake behaving cats. Future efforts include understanding the effects of evoked sensations on voiding and improving the integrity of the bonding between the flexible conductors and the lead wire.

NIH SPARC OT2OD025297
SPARC Program