Page 529 - IJB-10-6

International Journal of Bioprinting Bacteriorhodopsin-embedded hydrogel device

Figure 2. Topographical characterization of the fabricated hydrogel construct and the printability of the hydrogel. (A) Fabricated bacteriorhodopsin
(br)-embedded hydrogel construct with varying br concentrations. The blue filament represents a high concentration, while the red filament represents
a low br concentration. (B) Hydrogel filament printed at 19°C, where a lower crosslinking temperature resulted in an over-crosslinked filament. (C)
Hydrogel filament printed at 21°C, resulting in a well-crosslinked filament. (D) Hydrogel filament printed at 23°C, where a higher crosslinking temperature
resulted in an under-crosslinked filament. (E) Scanning electron microscopy (SEM) image of the br-embedded hydrogel construct. (F) SEM image of the
dried hydrogel filament from the br-embedded hydrogel construct. The sodium alginate film (right half of the image) formed through ionic crosslinking
provides additional mechanical strength. (G) The porous hydrogel structure allows free proton transfer within the construct. (H) The relationship between
loss modulus (G″) and storage modulus (G′) with respect to temperature. (I) The printing material exhibits shear-thinning behavior due to the presence
of sodium alginate. Shear-thinning is critical for extrusion-based printing methods, as it allows the material to flow through the nozzle while maintaining
its structure after printing. (J) UV-VIS absorption spectrum of hydrogels with and without br. The br-embedded hydrogel exhibits an absorption peak
around 568 nm, corresponding to the retinal absorption peak in br. No significant difference in the absorption spectrum was observed before and after
crosslinking. Scale bars: 1 mm (A–D); 100 µm (E); 20 µm (F); 10 µm (G). Abbreviations: gel-alg-pre: Hydrogel without br before crosslinking; gel-alg-post:
Hydrogel without br after crosslinking; gel-alg-br-pre: Hydrogel with br before crosslinking; gel-alg-br-post: Hydrogel with br after crosslinking.

the generation of a photocurrent when utilized as a character of br, but rather the combination of the proton
photoanode, as evidenced in prior studies. 19,21,29,55 In a pumping function of br and the effect of ITO conduction
constructed three-electrode photovoltaic cell with br change. Specifically, the differential part of the response
integrated into a hydrogel acting as the working electrode, comes from the br molecule in the hydrogel, and the
the photoelectrochemical analysis revealed a differential square-wave part of the response comes from the
pattern of photocurrent under continuous illumination, change of the potential of ITO glass under illumination
corresponding to the differential response associated with (Figure 3B). The ITO glass, even without photosensitive
br-based photovoltaic cells in which br functions in the protein, exhibits a square-wave photoelectric response
form of thin films. The typical photoelectrical response in our experiment. This could potentially stem from
(Figure 3A) is a composite waveform consisting of a the heat effect of light, as heating the ITO glass directly
differential response and a square wave-like response. This leads to a similar result. Therefore, a white LED, with a
response does not come solely from the photosensitive peak spectrum of 443 nm, could contribute to the square

Volume 10 Issue 6 (2024) 521 doi: 10.36922/ijb.4454