Chronic instrumentation with model microstimulators in an animal model of the lower urinary tract

Background: Microstimulators are a new type of neuroprosthetic device that should be considered for applications such as micturition control after spinal cord injury (SCI). These devices are small (less than 25 mm by 5 mm) and the electrodes are located on the ends of the stimulator. The aim of the current study was to develop methods for chronic implantation of model microstimulators (M-Micro) on the bladder wall and pelvic plexus of female cats. A postmortem evaluation of the effects of 3 months of implantation is reported. Methods: Techniques to produce the M-Micro are described. Four of these devices were implanted in 4 female cats and maintained after the initial instrumentation surgery and a second survival surgery for SCI (at T10). Using a single suture tied around the M-Micro, these devices were secured to the bladder wall or the fat pads adjacent to the pelvic plexus. Additional instrumentation was implanted, including 2 catheters in the bladder, 1 abdominal balloon, and electromyography electrodes in the urethral and anal sphincters. Postmortem observations of the location of the M-Micro on the bladder wall were conducted after fixation. Results: The animals' conditions were good. One animal was sacrificed early because of a skin infection. A single suture was sufficient to anchor the M-Micro. However, during the surgical implantation the pelvic plexus M-Micro ended up close to the bladder neck. Extensive fibrous connective tissue formed around the M-Micro and implanted catheters on the bladder wall. This appeared to result, in part, from multiple devices implanted on or near the bladder wall. Conclusions: These pilot studies showed that the M-Micro could be easily constructed and secured to the bladder wall or fat pads close to the pelvic plexus. There was a concern that the pelvic plexus location for the M-Micro ended near the bladder neck during the surgical implantation; however, these devices did not appear to migrate over this short, 3-month implantation period. The extensive connective tissue responses of the bladder wall to the tubes, wires, and M-Micro was a major concern. The M-Micro appears to be a good device to assess the potential of commercial microstimulators for use in micturition control.