The incidence of pathologies related to bladder dysfunction is clinically relevant, these including spinal injuries and neurological disorders. A considerable part of these illnesses is associated to urinary incontinence, which is not only cause of severe discomfort for patients, but in cases of poor or erroneous treatment it could lead to infections and tissue lacerations, with serious threats for health. A number of therapies are currently available for micturition control, however a definitive solution for real-time and adequate monitoring of bladder volume is still not available. Such a solution would allow the continuous probing of the filling state of the organ, thus avoiding the insurgence of two complications, i.e. excessive expansion of the bladder and its incomplete evacuation. This aid could work in cooperation with a wearable unit or also as feedback for already existing systems apt to urinary stimulation.
We herein propose an innovative design for a capacitive strain gauge, fabricated with a hybrid process that exploits organic and flexible materials as scaffold, metallic conductive layer as electrodes and an electrical insulator coating as protective and dielectric layer. The main challenge for this application is to design a strain gauge able to match the high elasticity of the organ under study by ensuring the sensor integrity in time, as these features hardly can be found in elastomers nowadays used in biomedical implants. The original prototype introduced in this work ensures a variation of capacitance that is proportional to the bladder tissue elongation, and it is able to accommodate the wide and repeated volume changes to which the organ is subject, without exposing the device components to continuous and recurrent mechanical deformations. The proposed design allows for a discrete strain analysis exploiting a principle similar to a linear encoder, and embeds contactless communication through an integrated RF antenna. In our work, we operate the system on an artificial bladder model, demonstrating contactless data read-out via a passive communication system, and thus paving the way towards testing on more realistic ex vivo and in vivo models.
The sensing system proposed in this work thus aims at providing a novel approach to the long-standing issue of bladder volume measurements, by advancing a design that could in principle allow for easy and reliable monitoring, not achievable with current technologies. Further developments of this approach could lead to the coupling of such device to implantable stimulating ones, hence helping to restore the original bladder functionality in patients, as well as enable direct data communication and control though smartphones or other handheld devices.