Page 247 - IJB-10-4

International Journal of Bioprinting Cell viability in printing structured inks

tissues, as well as advancements in corresponding cell- pressure and shear forces on cells. Cell viability losses during
compatible manufacturing and cell regulation processes. such processes have been previously reported by Blaeser
6
5
Cell viability stands as a critical consideration in et al. in the encapsulation of mesenchymal stem cells
27
7
engineered tissues, and it is extensively characterized in during alginate printing. In recent research, printheads
28
biofabrication. Low cell viability is generally unacceptable, employing cross-mixing principles were employed for
primarily due to its direct impact on cell proliferation, constructing gradient tissue structures. A reduction in
migration, and differentiation, all of which are essential pressure and shear forces by 3.196e+4 Pa and 0.368e+2 Pa,
for tissue formation. Elevated rates of cell death due to respectively, was observed when compared to conventional
8
inappropriately chosen materials and processes can lead static mixer-based printheads. Nevertheless, this pertains
to unstable tissue structures, incomplete tissue formation, primarily to the construction of gradient tissue structures,
and even the inability to construct functional tissues. 9 and the examination of cell viability during the 3D printing
Consequently, there is an urgent need for in-depth research is still lacking. Considering the concurrent requirement for
to achieve high cell viability within the engineered tissue favorable shear-thinning properties in printing materials
29
structures. to achieve printability and tissue formation, there is a need
for a universal guidance to enhance cell viability, one that
Three-dimensional (3D) printing technology, capable
of fabricating intricate scaffold structures that facilitate can mitigate the fluid pressure and shear forces exerted on
vascular growth, oxygen and nutrient transport, and the cells.
11
10
tissue cross-talk, has found extensive applications in Recently, a significant advancement in 3D printing
12
biofabrication. Specifically, it encompasses two main using structured inks has been reported, as illustrated
30
approaches : One involves direct fabrication of acellular in Figure 1A. Unlike the typical homogeneous inks
13
scaffolds followed by cell seeding, while the other entails commonly used in printer cartridges, these inks feature
the direct printing of cell-laden bioinks. In the former distinctive cross-sectional patterns, such as core–shell
approach, tissue construction is limited by the efficiency and symmetric configurations, enabling direct extrusion
and homogeneous distribution of cell seeding. 14,15 In the and resulting in the creation of diverse heterogeneous
latter, control over the spatial distribution of cells within the structures with specific extruded fiber cross-sections.
3D scaffold is achievable, but cell viability concerns arise These inks were prepared involving the use of molds, yet
from cell responses to the 3D scaffold fabrication process they ultimately maintained a seamless interface between
(e.g., pressure exerted on cells, alterations in material their components. Furthermore, this approach enables
16
17
properties, and factors like ultraviolet light ). Hydrogels, precise cell positioning within the structured inks. While
18
19
known for good biocompatibility, microporous the design and printing workflow for structured inks
structures, and high water content, provide a conducive has been introduced, considering the dimensions of
21
20
environment for cell adhesion and growth. extruded fiber cross-sections to determine ink properties
Extrusion-based 3D printing (E3DP) systems are and distribution, a challenge persists during the printing
widely employed in additive manufacturing due to their process. If cells are immersed in high-viscosity materials or
cost-effectiveness and versatility with a broad range of subjected to extrusion through small nozzles, it may lead
to potential cell mortality. Therefore, the consideration
biocompatible materials. The incorporation of sacrificial of cell viability remains an essential aspect of material
22
materials (e.g., gelatin) or the introduction of oxygen- design. Kang et al. conducted preliminary comparative
23
31
producing hydrogels has been reported to enhance cell
24
viability. Ouyang et al. developed a microgel-templated experiments on cell viability, using NIH/3T3 cells,
25
porogel bioink platform to introduce microporosity in comparing structured inks to conventional printing
3D-bioprinted hydrogels, resulting in increased metabolic methods. Their findings revealed an improvement in cell
26
activity and uniform mineral formation. Wang et al. viability within the group using structured inks. However,
utilized single-cell microalgae in in situ 3D printing to their investigation did not delve deeply into this aspect.
Consequently, we aimed to quantitatively evaluate fluid
generate scaffolds that continuously produce oxygen when forces, including pressure and shear stress, during the 3D
exposed to light, thereby promoting tissue formation even printing process to comprehensively address this research
under hypoxic conditions. However, despite post-printing gap and refine the material design guidelines for structured
validation of cell viability, the issue of considering fluid
forces experienced by cells, which can lead to cell death, has inks, with a specific focus on enhancing cell viability.
never been given significant attention. Typically, enhancing First, we assumed that extrusion-based 3D co-
printing resolution can be achieved by reducing nozzle printing using structured inks has potential advantages
size; however, this often leads to increased pressure on the for the viability of cells, inspired by the principles of direct
deposited bioinks during the printing process and imposes extrusion processes for heterogeneous structures through
Volume 10 Issue 4 (2024) 239 doi: 10.36922/ijb.2362