A Soft, Conformal, and Implantable Sensor for On-Demand Bladder Volume Monitoring

Reliable bladder volume monitoring remains a major unmet need for individuals living with an impaired bladder sensation. Current clinical methods provide only intermittent measurements, while recent implantable sensors often rely on localized sensing or relatively rigid interfaces that may limit conformability to the bladder and reliable monitoring of large volumetric changes. These limitations highlight the need for a soft, conformal, and low-power sensing platform capable of capturing bladder deformation during filling and emptying. We present a soft bladder interface (SBI) consisting of a stretchable piezoresistive composite layer that is integrated within a conformal elastomeric frame. The device uses a circumferential sensing architecture to mechanically conform to the external bladder wall without the need for sutures or adhesives and captures volume-dependent expansion. Developed through a rapid laser patterning prototyping approach, the SBI provides a scalable design adaptation for future personalization to different bladder geometries in preclinical animal models and potential human applications. The device was evaluated through benchtop phantom bladder and in vivo rodent studies and demonstrated repeatable volume-dependent responses and real-time bladder volume monitoring. To enable wireless readout, the sensor was interfaced with a commercially available battery-free near-field communication (NFC) evaluation platform, externally powered by a smartphone and connected to a custom-developed application, as a proof-of-concept for on-demand wireless sensing.