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Duan et al. Soft Sci. 2025, 5, 4 https://dx.doi.org/10.20517/ss.2024.46 Page 9 of 15

In conclusion, the observed trend of parameter alterations and the substitution of the expression for bladder
impedance, Z , leads to the conclusion that human bladder impedance, Z , decreases as urine storage
b
b
volume increases. Consequently, researchers can further ascertain the state of the human bladder by
investigating the nonlinear inverse relationship between the change in urine storage volume and the change
in bladder impedance.

Integration and characterization of a wireless electronics
A fully integrated wireless bladder status monitoring electronic device was developed based on the assembly
of a biocompatible electrode patch and reusable PCB. The PCB contains a microcontroller unit (MCU), in
which STM32F103C8T6 serves as the terminal master controller with a high-performance and low-power
32-bit RISC processor ARM Cortex-M4, a diverse range of peripheral interfaces, including a timer, an
analog-to-digital converter (ADC), inter-integrated circuit (I C), and communication interfaces such as a
2
universal asynchronous receiver/transmitter (UART) and a serial peripheral interface (SPI) [52,53] . This
internal special composition facilitates communication with other modules on the board or external
smartphones. The hardware block diagram of the system, which employs the STM32F103C8T6 as the
principal controller, is depicted in Figure 3C. This diagram includes the UART1 serial port circuit, keypad,
and liquid crystal display (LCD). This design is to eliminate the host computer and integrate the
programmable low-power Bluetooth (BLE) module for remote data transmission and monitoring between
the devices. The module is integrated with a microcontroller for signal processing and wireless
communication, Supplementary Figure 5A and B illustrates the BLE module schematic and pin diagram,
and microcontroller system for UART serial communication, the communication protocol that is the
UART communication protocol. The microcontroller’s receive (RX) and transmit (TX) ports are connected
to the corresponding ports on the JDY-31 module, enabling the transmission of data and receipt of
commands. Furthermore, the device incorporates a signal processing unit (SPU) and three buttons, which
[54]
serve as the overall on/off key of the system and the key for setting alarm thresholds . Additionally, it
features an LCD for real-time display of monitoring data and a rechargeable 5 V lithium battery with a
capacity of 2,400 mAh for power supply. This is followed by the fabrication of the board [Figure 3D].

After designing the schematic based on the overall system architecture and hardware requirements, it was
imported into the PCB design software, Altium Designer. The circuit board was partitioned and layered
according to electrical performance requirements. The mechanical layer was configured to set the
dimensions and mechanical details of the main control board, while the signal layer was used for
component placement, routing, and soldering. The component layer was designated for resistor soldering
and silkscreen printing. Signal, ground, and power lines were routed in the inner layers to ensure
compliance with impedance control standards. Component positions were adjusted accordingly to finalize
the PCB layout, and the board was subsequently prepared for fabrication [55,56] . Further details can be found
in the Supplementary Materials.

The efficacy of this wireless monitoring system was assessed by spraying varying concentrations of NaCl
solution (0.05-0.25 M) onto the electrode patches of the fully integrated electronic system [Figure 3E],
which was selected due to the substantial presence of chloride and sodium ions in human sweat. The system
exhibited a linear relationship between the height of the response current and the concentration of the
solution, with a regression model as shown in Figure 3F, with a correlation coefficient of 0.9185.
Furthermore, the system demonstrated the same linear relationship at different frequencies [Supplementary
Figure 6A]. Figure 3G illustrates the resultant plot of the system monitoring in the presence of interfering
molecules in sweat. A series of interfering molecules, including H O, urea, dextran, acetic acid, ethanol,
2
potassium chloride, ascorbic acid, and magnesium chloride, were sprayed onto the electrode surface. In
contrast, the control group mimicked dry human skin without spraying the solutions. The responses were