Page 532 - IJB-10-6

International Journal of Bioprinting Bacteriorhodopsin-embedded hydrogel device

concentrations can be structured into specific patterns, preceding pixel is 0) and the value of the photocurrent at
allowing for spatially diverse stimulation. the onset of the pixel, and a quantitative relationship can be
The light intensity-sensitive characteristic of br- determined after calibration. Considering a pixel i, its gray
embedded hydrogel was further verified by grayscale pattern value P can be obtained through the following equation:
i
recognition, as illustrated in Figure 5. The grayscale pattern
was encoded to different voltage levels corresponding P =P + C × I, P = 0 (II)
i–1
0
i
i
to varying grayscale values. The signal containing time-
modulated voltage levels was generated using the arbitrary
waveform generator and used to modulate the power of In this equation, I represents the magnitude of the
i
the laser source using AC modulation. The information photocurrent at the onset of pixel i and takes a positive value
contained in the grayscale pattern was therefore converted when the photocurrent flows from the anode to the cathode
to time-modulated illumination with varying intensity, and a negative value when the photocurrent flows from
with each pixel corresponding to one second of illumination the cathode to the anode. C is the constant obtained after
and the gray value corresponding to the light intensity. Due calibration that represents the linear relationship between
to the differential response and the light intensity-sensitive the amplitude of light intensity change and the magnitude
characteristic of br-embedded hydrogel, the gray value of of the photocurrent. The constant C is positively correlated
each pixel can be determined based on the gray value of with the concentration of br in the br-embedded hydrogel
its preceding pixels (e.g., for pixel 1, the brightness of the and is influenced by other factors, such as the composition

Figure 5. The grayscale pattern recognition demonstrates the light intensity-sensitive property of bacteriorhodopsin (br)-embedded hydrogel. (A) The
1D grayscale pattern was pixelized and encoded into a staircase wave signal with voltage levels corresponding to the gray value of each pixel. The signals
were generated using an arbitrary wave generator and used to modulate the laser generator through AC modulation. (B) The photocurrent response of
the encoded patterns. The two response curves correspond to the pattern with ascending brightness and descending gray values, respectively. A positive
photocurrent indicates an increase in gray value, while a negative photocurrent indicates a decrease in gray value.

Volume 10 Issue 6 (2024) 524 doi: 10.36922/ijb.4454