Page 492 - IJB-9-6

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

case of nozzle walls, there may be an increase in shear stress shear-thinning rheological behavior of silk due to β-sheet
at the strand’s periphery, leading to lowered cellular viability. crystallization and gelatin’s high viscosity enhanced the
It is likely that the peripheral filaments tend to spread and bioink’s printability, and the bioink viscosity value was the
form cellular networks more quickly because they are in the lowest in the range of 25–35°C, enabling printing within
vicinity of the hydrogel surface and are not encapsulated this temperature range. Furthermore, high cellular survival
completely [197] . A functional difference between two cells was ensured when gelatin and silk concentrations were 7%
may also be the result of morphological differences between and 1.5% w/v, respectively.
their filaments on the exterior and the interior. When Since compressive and tensile behaviors of the
this matter is viewed from the perspective of bioprinting bioprinted hydrogels are critical, Yang et al. [204] used
approaches, for example, in an acoustic bioprinter, a pool of collagen (15 mg/mL) and alginate (15 mg/mL) mixed
bioink is directly injected with cell-encapsulated droplets with new-born Sprague Dawley chondrocytes (10 × 10 6
and deposited over the surface . Due to its nozzle-free cells/mL) as a bioink to print 3D six-layer constructs
[67]
design, this technology avoids clogging issues and prevents (2 × 2 cm ) and assessed their mechanical features. Uniaxial
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detrimental shear stresses, heat, and pressure commonly tension tests were conducted at ambient temperature
experienced in other bioprinting methods [198,199] . with constructs stretched at 2 mm/min. Besides, cell-
The bioprinting of embedded cells has previously been laden gels with a maximum displacement of 1 mm and a
done employing inkjet and extrusion technologies [200,201] . speed of 0.1 mm/min were analyzed for their compressive
For maintaining cell viability, a PBHs was used to suspend strength. Compared with the alginate alone (~28 kPa),
cells in the inkjet fluid reservoirs utilized for bubble- collagen increased the stiffness of collagen/alginate-
jet technology or closed fluid reservoirs utilized for printed hydrogel by nearly 1.87 times. Additionally, the
piezoelectric technologies in order to buffer them from printed composite hydrogel (~41 kPa) showed remarkable
temperatures between 200 and 300°C [202] . Additionally, strengthening and toughening effects with 162.08% greater
inkjet and extrusion technologies subject cells and protein strength and toughness than the alginate gel (~19 kPa).
structures to remarkable mechanical and thermal stresses.
Exhibiting poor directionality of droplets or continuous 4.2. Biocompatibility considerations
filaments, achieving non-uniform droplet sizes, existing Biocompatibility refers to the material’s ability to respond
mechanical shear stress of ejected cellular materials at to a specific host environment [205] ; within this context, it is
the nozzle, and having routine nozzle clogging problems essential to consider the biocompatibility of cell-laden PBHs
are other drawbacks of these techniques; as a result of the during bioprinting, in vitro maturation, immunogenicity
mentioned obstacles, large numbers of “empty” droplets of hydrogels, and long-term effects of the gels.
are generated, contributing to significant inefficiency . Cellular viability and proliferation can be influenced
[66]
Although the nozzle geometry has no impact on by the hydrogel composition once bioinks have been
the droplet size or ejection directionality, it has been deposited. In numerous matrix proteins and as mentioned,
demonstrated that the geometry can cause damage to cells the RGD motif improves the cell–matrix interactions and
or denature protein structures in printing methods like can promote osteogenic differentiation and cell survival.
inkjet and extrusion. Since acoustic bioprinting employs It is also possible to modify hydrogels with other side
very short durations and low wavelengths, its effects on groups and sequences like phosphate groups, covalently
cell membranes and protein structures are negligible. It is bound GFs, and heparin-binding domains, with the aim of
also noteworthy to mention that during ejection, no high increasing the creation of mineralized matrices and bone
[206,207]
pressure or heat is applied to the fluid [66,203] . tissue possessing comparable mechanical features .
Compared with synthetic polymers, protein-based
Therefore, optimizing the PBHs’ concentration to polymers like collagen, silk, keratin, serum albumin, and
obtain optimal viscoelasticity properties during bioprinting elastin have cell-adhesive peptide sequences that provide
is necessary. Concerning this matter, the investigation conducive microenvironments suitable for enhancing cell
conducted by Singh et al. [136] focused on the development of survival and proliferation [208] . In addition, physiological
silk-gelatin bioinks for the cartilage tissue’s microextrusion and biological cues present in structural proteins play a
bioprinting. In the first step, silk (0.5% to 2% w/v) and crucial role in bioink development. Additionally, protein-
gelatin (1% to 9% w/v) hydrogels loaded with porcine based materials are not only environmental friendly and
auricular chondrocytes (1 × 10 cells/mL) were prepared. renewable but also strong, elongated, tough, and slowly
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Afterward, the viscosity and modulus were evaluated in degradable. As an example, silk fibroin is one of the
the range of 4–45°C so as to obtain a viscoelastic range for most popular PBHs used in bioprinting. It undergoes a
their bioink. They illustrated that the combination of the remarkable structural transition from a random-coil to a

Volume 9 Issue 6 (2023) 484 https://doi.org/10.36922/ijb.1089