Page 88 - Read Online

Page 10 of 15 Duan et al. Soft Sci. 2025, 5, 4 https://dx.doi.org/10.20517/ss.2024.46

then tested sequentially. The presence of these interfering molecules had no significant effect on the current
response, confirming the good selectivity of the system. In particular, the immunity of the system was
measured at 10, 50 and 100 kHz [Figure 3H and Supplementary Figure 6B], where the impedance change
was large at 10 kHz. This indicates that the interfering molecules will be somewhat disruptive to the system
at low frequencies. In contrast, the impedance change was weak at the experimental frequency chosen in
this paper, 50 kHz. This again confirms the suitability of the system. Long-term stability is a critical factor
for sensor performance, particularly in applications requiring consistent measurements over extended
periods. Stability can be influenced by material degradation, environmental fluctuations, and repetitive
loading . To minimize impedance drift over time, this study implemented measures such as optimizing
[57]
electrode material properties and applying protective encapsulation to limit external influences. The
stability of the device materials during long-term usage is further discussed in Supplementary Table 2.
Additionally, the impedance changes of the bladder sensor were measured over a 10-day period, as shown
in Figure 3I, to assess its long-term stability. The sensor was applied to the human skin and the impedance
was measured every 24 h. The results demonstrated that the relative standard deviation (RSD) of the sensor
was 0.791%, which confirmed the operational stability of the system.

Validation and evaluation of a wireless bladder electronic device
During the process of bladder emptying to filling, urine storage continues to rise and impedance values tend
to decrease, as shown in Figure 4A. The utilization of wearable technology for the analysis of human
bladder impedance represents a low-risk, low-cost and easy-to-use approach to the remote monitoring of
patients or family members, when compared to invasive and US-based analyses. In order to validate the
value of the designed electronic device for measuring bladder status, six participants of varying ages (three
males and three females) were monitored for bladder status. Prior to the commencement of the experiment,
the skin of the subject must be cleaned and sterilized. Thereafter, two measurement electrodes are to be
adhered to the lower abdomen of the subject in a symmetrical manner, at a point 10 cm below the navel and
5 cm from the midline of the navel [58,59] . The electrodes are mounted in the position illustrated in Figure 4B.
The designed electronics and the commercial equipment were connected to the electrodes, and the
appropriate measurement parameters were set: start frequency 50 kHz, termination frequency 60 kHz.

Following the emptying of the bladder by the tester, the designed electronics and commercial equipment
were activated for a 30 min measurement of the bladder impedance. After 30 min, the tester consumed
500 mL of drinking water in one sitting, maintaining the designated sitting posture. Initially, the
measurement was conducted using commercial equipment. The current frequency delivered to the
electrodes was 50 kHz, with a frequency scanning interval of 1 min, enabling the bladder electrical
[60]
impedance to be measured at regular intervals . Subsequently, the measurement was conducted using a
designed electronics. The bladder electrical impedance per minute was recorded by observing the data
displayed on the LCD screen on the system board or the mobile phone application [Figure 4C]. The
measurement process continued until the tester indicated that they wished to urinate, at which time the
tester’s bladder was in a full state. Following the conclusion of each experimental series, the data obtained
from the two groups of devices were subjected to comparison and analysis. The resulting measurement
outcomes are presented in Figure 4D-I.

The test results indicate that the magnitude and rate of change in bladder impedance may exhibit inter-
individual variation across participants over time. This is consistent with the increase in bladder volume as
the bladder fills with urine. The converted impedance data showed a decreasing trend in bladder impedance
as urine accumulated, indicating an increasing trend in bladder volume. Particularly, bladder impedance
decreased rapidly approximately 10 min after participants drank water. Upon reaching a predetermined
threshold, the mobile device would activate a continuous vibration alarm to prompt the user to urinate
promptly.