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International Journal of Bioprinting Bioprinting cell-laden protein-based hydrogel

viable and preserved their survival within various bioink irradiation for 60 s. The results indicated that the swelling
compositions after 14 days of cultivation (Figure 5D) [137] . ratio was strongly influenced by the crosslinking density
of the 3D network; a higher crosslinking density caused
4.3. Crosslinking considerations segments between joint points to become smaller, thereby
A bioprinted construct’s degradation rate can be impacted preventing swelling. As a result of the photo-crosslinking
by its composition, concentration, temperature, mechanical of GelMA polymer chains, a covalent crosslinking network
force, and cell culture medium; thus, the degradation formed, which prevented the hydrogel from dissolving.
rate of the bioprinted structure should be considered [164] . The slow degradation of MC/GelMA hydrogel ensured that
Specifically, the degradation rate of the PBHs is highly it retained its mechanical properties so that newly formed
dependent on the β-sheet crystals’ orientation, content, and tissues and cells could be supported during regeneration.
non-crystalline domains [210,224] . The mechanical properties The MC/GelMA bioink’s shape integrity was characterized
of bioinks may decrease too rapidly during culturing. To by its complex modulus and yield stress, which were higher
further enhance the integrity of the printed structures, than those of the pure MC ink, resulting in self-supporting
crosslinking is most commonly performed for the printing behavior once printed. Additionally, human primary
of the dispensed cell-laden PBHs as stated [225] . It was osteoblasts that were encapsulated within the MC/GelMA
mentioned that there are several kinds of crosslinking hydrogels illustrated a cell survival of over 95%. This
approaches used in PBHs bioprinting, including physical, work emphasizes the importance of rheological features
chemical, and enzymatic crosslinking before, during, and and the post-crosslinking process in the production
after printing. Furthermore, thermal crosslinking can be of physiologically scaled tissue implants [228] . Overall,
used to print PBHs; in this case, temperature-induced the selected crosslinking method for PBHs bioprinting
gelation improves the printed construct’s initial stability impacts cellular viability and behavior, and the application
since it is faster than the gelation by Ca cations as physical should be considered while selecting the appropriate
2+
crosslinkers. Nevertheless, it is challenging to precisely technique [29,229-231] .
control how much crosslinking occurs, and overheating
in this process may adversely affect cell viability. Natural Printed droplets do not merge in these constructs,
hydrogels, such as collagen, will lose mechanical strength thereby increasing their mechanical stability. In addition to
because of enzymatic hydrolysis, and thermally sensitive enhanced cellular functions, physical crosslinking produces
hydrogels can also lose their shape when the environment’s no toxic byproducts and contributes to rapid gelation [232] .
temperature changes [120] . For instance, due to the collagen Notably, the plasma membrane can initially become
helices’ collapse to random coil structures at 30–35°C, damaged at low points in cells printed with low fluences
the dissolved collagen’s storage modulus and viscosity and short gelation time, but the cells will recover rapidly
are rapidly reduced without gelation; hence, the thermal through the sealing mechanism [233] . Consequently, despite
sensitivity of PBHs should be noticed in the bioprinting providing a cushioning effect, all polymer concentrations
process [121,211] . Owing to this subject, scholars should require a suitable gelation time [234] . If the encapsulation
meticulously select hydrogels and their associated 3D process fails, the cells will not adhere to the scaffold and
structures in a way that the degradation rate will be proliferate on the well plate instead; consequently, the cells
[195,235]
appropriate. One of the most common approaches in are not able to be 3D cultivated .
bioink printing is the employment of UV crosslinking to For bioprinting, Visscher et al. [236] developed cartilage-
augment mechanical characteristics and degradation after derived decellularized ECM-based photo-crosslinkable
bioprinting [169] . Nonetheless, variations in the UV exposure porcine auricular cartilage hydrogels/methacrylate
times decrease cell viability by increasing crosslinking after (cdECMMA). Subsequent to the printing, cdECM-based
bioprinting [226] . Post-printing crosslinking can provide constructs were chemically modified by methacrylate
hydrogels with a higher modulus, as well as longer rates of reactions, providing structural integrity. Moreover, the
degradation in vitro and in vivo, together with providing bioink was prepared with a solution consisting of 37.5 mg/
cells with proper stiffness [218,227] . Within a brand-new mL gelatin type A, 3 mg/mL HA, and photoinitiator (0.1%
assessment, bioprinting of methylcellulose (MC)/GelMA v/v, Irgacure 2959). A UV light intensity of 200 mW/cm
2
bioinks with great shape integrity was performed. This was used for 2 min to induce photo-crosslinking in this
research project introduced a new type of MC/GelMA bioink formulation, and various concentrations (20, 30,
bioink that could maintain its shape integrity over several and 40 mg/mL) of cdECMMA hydrogels were produced.
months in the biological media. Unlike pure MC inks, With the increment of cdECMMA concentrations, the
distorting and dissociating in the biological media, MC/ hydrogels’ stiffness was considerably enhanced (20 mg/mL:
GelMA bioinks maintained their stability because of 3837 ± 462 Pa, 30 mg/mL: 10381 ± 1339 Pa, and 40 mg/mL:
the GelMA’s permanent photo-crosslinking under UV 25,050 ± 2573 Pa). In addition, all cdECMMA constructs’

Volume 9 Issue 6 (2023) 487 https://doi.org/10.36922/ijb.1089