Urination is an essential physiological process to excrete wastes from the body. This process is precisely controlled by the nervous system. The damage or disorder of the nervous system caused by trauma or systemic nervous diseases can lead to urinary dysfunction. Individuals with urinary dysfunction must rely on proper and adequate bladder management. Hence, developing monitoring systems that provide notification of the need to evacuate is of critical importance for those patients with disabled bladder sensory awareness. Monitoring bladder urine volume/pressure can also provide important information for directing treatment. In the present study, we aimed to develop a stable and reliable monitoring electrode for real-time detecting the bladder activity and EMG signal.

In this work, we developed a simple one-step high-temperature evaporation process. A soft isotropic stretchable electrode with excellent performance can be prepared by evaporating gold on an eco flex-20 substrate with special evaporation parameters. By using rat model, we performed cystometry under anesthesia simultaneously monitoring intravesical pressure, detrusor EMG signals, and device resistance to evaluate the electrode's potential for short-term and long-term monitoring of bladder activity. By using the rat model of neurogenic bladder dysfunction induced by spinal cord injury, we evaluated the electrode's ability to monitor non-voiding contractions and to provide microcurrent electrical stimulation to improve bladder hypersensitivity.

The electrode has an isotropic tensile ratio of more than 200% and a unidirectional tensile ratio of more than 700%. Moreover, under the condition of about 600% area change, the electrode can be stably stretched for 5000 cycles; Under various stretching rates and 200% stretching rate, the electrode can realize 50000 stable unidirectional stretching cycles. We achieved bladder strain sensor signals monitoring for up to 10 days and bladder EMG signals monitoring for up to 28 days. The persistently elevated resistance signals correlated with the accumulated bladder capacity during storage. And external devices detected significantly enhanced smooth muscle EMG signals and sudden decreases in strain sensor resistance during elimination. Additionally, in the neurogenic bladder dysfunction rat model, obvious resistance signal spikes were detected during voiding and non-voiding contractions. More importantly, the difference between the beginning and end of each resistance signal spike can be used to distinguish between voiding contractions and detrusor overactivity. In addition, electrical stimulation driven from our proposed electrodes successfully induced bladder contractions in control rats. Moreover, long-term microcurrent bladder stimulation for 7 days reduces the frequency of non-voiding contractions in the neurogenic overactive bladder rat model.

Patients with neurogenic bladder are always suffered from disabled bladder sensory awareness and detrusor overactivity. The present study designed an implanted isotropic stretchable bladder electrode that can help monitor bladder urine volume/pressure. More importantly, this electrode can distinguish between voiding contractions and non-voiding contractions. The present stretchable bladder electrode has great value in clinical application for monitoring bladder volume/pressure as well as bladder detrusor overactivity.

These results confirm that our proposed electrode is a highly feasible, clinically relevant implantable device for long-term monitoring bladder urine volume/pressure. This bladder electrode can also monitor non-voiding contractions and provide microcurrent electrical stimulation to improve bladder hypersensitivity.

Continence 7S1 (2023) 100765
DOI: 10.1016/j.cont.2023.100765