Across the globe, more than 400 million people are affected by an overactive bladder (OAB), and within Europe, it affects 17 % of people, with that proportion increasing to 30-40 % for those over the age of 75. OAB can have a devastating effect on patients’ lives, since it produces a sudden and intense need to pass urine, with the patient having almost little or no control. It is known that stretch of the bladder wall is linked to the need to pass urine since it gives an indication of bladder fullness; however, until now, it has not been possible to fully determine bladder fullness without using complex and invasive surgical procedures. We present a fully biocompatible, soft, stretchable sensor device, capable of monitoring minuscule changes in the bladder wall, which can lead to the development of new treatment options for various urological conditions, including OAB.
We have developed sensors comprising thermally evaporated Cr/Au thin films (~ 150 nm) on compliant, stretchable polyurethane (PU) film. When stretched, sensor resistance changes from a few Ω’s, to tens or even hundreds of Ω’s depending on sensor dimensions. We demonstrate repeatable sensor response up to at least 70 % stretch, with sensitivity exceeding 20 Ω/mm. Furthermore, the sensors show almost no hysteresis when subjected to repeated cycling tests between 0 and 50 % stretch, making them suitable for application on the bladder. The sensors have also been tested in vitro on a pig’s bladder, subjected to repeated filling and emptying cycles to mimic natural bladder behaviour. Sensors were attached to the bladder wall using an optimised biocompatible adhesive hydrogel film, which allows sensor stretch to be retained, whilst providing strong adhesion as the bladder constantly cycles between full and empty. As the bladder fills, the sensor detects minute changes in the bladder wall (micromotions) using changes in resistance as a function of stretch; and this resistance is used to correlate stretch with fullness, and can provide an early warning system for OAB patients of the need to pass urine. Our soft, stretchable, biocompatible sensors pave the way for fully implantable health monitoring systems of the future.
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