Irritable bowel syndrome and overactive bladder (OAB) syndrome are becoming more common in people who do not show evidence of infectious diseases or other known conditions but instead report sudden onset of symptoms.
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A research study published in Biosensors and Bioelectronics has proposed a novel, ultra-soft hydrogel-based bladder activity sensor that can monitor bladder activity and electrical muscle signals simultaneously.
What Is an Overactive Bladder?
Overactive bladder syndrome is a medical disorder that causes an uncontrollable need to urinate regularly.
Individuals with the condition may even get up in the middle of the night to urinate, despite the absence of any underlying sickness. While the ailment is rarely life-threatening, it may interfere with the patient's everyday activities, lowering their quality of life.
The condition can cause extreme discomfort, limiting normal daily activities and leading to depression and anxiety. Neglecting an overactive bladder can also cause chronic ailments in the long term, including renal malfunction and kidney failure.
Why Are the Existing Treatments Inadequate?
While medications have been used to treat OAB, they have not been effective in severe cases.
Device-based neuro-modulatory techniques like sacral or tibial nerve stimulation have been suggested in recent decades. These procedures involve the electrical stimulation of nerves linked to the bladder to minimize an OAB.
One of the potential issues with these techniques is that bladder activity is not monitored during nerve stimulation. This could lead to adverse effects because of excessive nerve stimulation or even make the treatment ineffective.
Researchers have been working on selective or closed-loop nerve stimulation techniques to overcome this issue. Still, these methods have yet to prove successful in bladder control due to the absence of effective methods for monitoring bladder activity.
Limitations of Existing Bladder Activity Monitoring
Previously developed bladder activity monitors contained silicone-based elastomers, which have much higher elasticities than the human bladder. This mechanical disparity may result in physical injury to the contacting bladder tissue, causing significant irritation and blockage of normal bladder movements.
Some of these monitoring devices have been shown to work by being entirely wrapped around the bladder of a mouse, as opposed to being attached directly to the bladder tissue surface.
This method makes the surgery for human implantation almost impossible. As a result, an ultra-soft sensor with a lower elastic modulus that can be attached easily to the bladder surface is preferable for clinical applications.
Highlights of the Present Study
The newly developed sensor is multifunctional and can simultaneously measure bladder expansion/contraction and electrical muscle signals, thus accurately monitoring the bladder's neurological and mechanical state for the micturition reflex.
The hydrogel-based sensor is low modulus and can adhere to the surface of the bladder, making it suitable for clinical translation.
The sensor, comprising an ultra-soft hydrogel coupled with structurally engineered islets (USH-SI), was developed by the research team on the assumption that comprehensive electromechanical measurement is essential for correctly monitoring the symptoms of an overactive bladder.
The USH-SI sensor was fabricated using two components, polyacrylamide hydrogel and a thin layer of gold electrodes.
The gold electrodes were sputtered onto the hydrogel surface, and the hydrogel was then patterned into the desired shape using a laser. The researchers placed the USH-SI sensor on the bladder and tested it on rats.
Important Findings
The researchers observed a high correlation between bladder expansion and EMG signals, indicating that EMG could be used as an additional digital phenotype for OAB.
The USH-SI sensor showed several advantages over previously reported bladder sensors. Its ultra-softness allowed it to seamlessly adhere to the surface of the bladder without causing damage or inflammation.
The USH-SI sensor could detect a weak bladder contraction that was not detected using commercial EMG electrodes. The researchers noted that the USH-SI sensor could monitor the electrical activity of the bladder without significant motion artifacts, making it a reliable method for detecting OAB.
This real-time monitoring of bladder activity could serve as feedback for neuromodulators, enabling fully-automated personalized treatment for OAB.
The quantitative analysis of EMG signals using the OAB model could provide a better understanding of the disease and facilitate the development of more effective treatments.
The researchers suggest that their approach can pave the way for developing closed-loop neurostimulation modalities that automatically adjust nerve stimulation based on bladder activity, leading to fully-automated personalized treatment for OAB patients.
"We combined the USH-SI sensor with a neural stimulator targeted to treat overactive bladders, a chronic condition," remarked Professor Sung-Min Park, an author of the study.
This allows for monitoring and neural stimulation simultaneously. We expect it to be a platform that can be applied to other internal organs.
Professor Sung-Min Park, POSTECH
Reference
Oh, B., Lim, Y.-S. et al. (2023). Ultra-soft and highly stretchable tissue-adhesive hydrogel based multifunctional implantable sensor for monitoring of overactive bladder. Biosensors and Bioelectronics. Available at: https://doi.org/10.1016/j.bios.2023.115060
Source: Pohang University of Science & Technology (POSTECH)
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