Page 528 - IJB-10-6

International Journal of Bioprinting Bacteriorhodopsin-embedded hydrogel device

staircase waves with various waveform characteristics. printing material with and without br exhibited similar
The AWG was linked to the 543 nm green laser generator rheological behavior, with only a 1°C difference in sol–
to modulate the light source using transistor-transistor gel transformation temperature. In this study, the nozzle
logic (TTL) and AC modulation. The modulated light was temperature was set at 20°C, slightly lower than the sol–gel
subsequently employed as light stimuli on the photovoltaic transformation point (Figure 2H), resulting in a slightly
cell based on the br-embedded hydrogel construct. over-crosslinked structure. Meanwhile, the substrate was
This hydrogel construct was then connected to the cooled to 11°C, accelerating the gelatin’s crosslinking
electrochemical workstation to record the photocurrent kinetics. Sodium alginate was selected for its suitability
data. To characterize the spatial pattern recognition in extrusion-based printing due to its shear-thinning
function, br-embedded hydrogel was fabricated into properties (Figure 2I). The incorporation of Ca² ionic
+
distinctive patterns, and the photocurrent data of the crosslinking further enhanced the structural robustness,
captured under the illumination of a moving laser spot. ensuring stability above the sol–gel transition temperature.
Three hydrogel patterns, containing one to three parallel The calcium alginate (Figure 2F), formed during ionic
hydrogel filaments, respectively, were fabricated onto crosslinking, protected the construct from environmental
an ITO glass substrate and constructed to form three effects. The rheological profile supports sodium alginate/
photovoltaic cells. The 543 nm green laser was focused to gelatin dual-crosslinking as an excellent choice for
form a laser spot of 2 mm diameter and moved across the the intricate fabrication of the br-embedded hydrogel
photovoltaic cells at a constant speed. The photoelectrical construct. With the hydrogel’s exceptional printability
response was then recorded using the electrochemical and the versatility of extrusion-based printing, various
workstation, which was used to reconstruct the spatial structural patterns can be achieved. Furthermore, the
pattern of the hydrogel construct (Figure 1C). characteristic absorption peak of br was well-preserved,
and the crosslinking process did not affect the absorption
2.5. Statistical analysis spectrum (Figure 2J). The absorption spectrum confirmed
All values are expressed as the mean ± standard deviation the retention of the br molecule within the hydrogel,
and were analyzed using Prism software (GraphPad Inc., displaying minimal changes in peak absorption wavelength
USA). Statistical analysis was performed using Student’s
t-test or one-way analysis of variance (ANOVA). and intensity after immersing the br-embedded hydrogel
in DPBS for seven days (Figure S1, Supplementary File).
3. Results This indicates the functional stability of the br-embedded
hydrogel in aqueous environments. A swelling experiment
3.1. Hydrogel construct fabrication and was conducted to assess the morphological stability of the
characterization hydrogel. The weight and diameter of the hydrogel structure
The hydrogel exhibited excellent printability, resulting in increased significantly following ionic crosslinking of
a clear, patterned construct with varying br concentration sodium alginate and remained relatively stable for 36
(Figure 2A). The blue hydrogel filament indicates high br h, with no significant changes observed (Figure S2,
concentration, while the red filament represents low br Supplementary File). These findings demonstrate that the
concentration, demonstrating the capability of fabricating br-embedded hydrogel maintains structural integrity and
hydrogel structure with varying br concentration using consistent morphology post-fabrication.
extrusion-based printing. A slightly over-crosslinked
hydrogel construct (Figure 2B) demonstrated suitability In addition to its excellent printability, the br-
for functional devices due to its high mechanical strength. embedded hydrogel demonstrated high biocompatibility
66
Over-crosslinked (Figure 2B), well-crosslinked, (Figure 2C), when combined with NPCs (Figure S3, Supplementary
and under-crosslinked (Figure 2D) hydrogel filaments were File). A live-dead assay conducted on day 1 revealed
fabricated by adjusting the temperature of the printing an average cell viability of 91.09%, indicating that the
nozzle, leveraging gelatin’s thermal crosslinking properties. br-embedded hydrogel is well-suited as a supportive
In addition to flexibility, the porous structure of the hydrogel matrix for cell encapsulation. Moreover, a calcium assay
pattern (Figure 2E–G) facilitates proton transfer. confirmed neural activity in NPCs embedded within the
hydrogel after six days of culture. These results highlight
The rheological characteristics are crucial for printing the br-embedded hydrogel as a promising biocompatible
materials undergoing sol–gel transformation. The hydrogel, material for biological applications.
composed of sodium alginate and gelatin, underwent dual
crosslinking to optimize both printability and structural 3.2. Photoelectrochemical characterization
integrity. Gelatin’s thermal crosslinking allowed for When exposed to light, br induces a flow of protons
precise viscosity control via temperature adjustment. The through protonation and deprotonation, resulting in

Volume 10 Issue 6 (2024) 520 doi: 10.36922/ijb.4454