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Materials Science in Additive Manufacturing From 3D printed molds to bioprinted scaffolds

scaffolds, will potentially enhance the printing experience with soft bioinks while preserving cell durability
and viability.

Keywords: 3D Bioprinting; Vat polymerization; Tissue engineering; 3D molds; Peptide hydrogels; Soft bioinks

1. Introduction thrombin blend fugitive ink. The cell-laden ink made of
gelatin, fibrinogen, transglutaminase, and thrombin, was
Conventional additive manufacturing technologies cast into the mold and the sacrificial ink was perfused out
can be classified into three main technologies: material of the construct. The mold was used because, in the former
extrusion, material jetting and vat polymerization [1-7] . In process of indirect extrusion-based bioprinting (EBB),
addition, they can be combined to give rise to alternative the thick bioprinted constructs could not be perfused
biofabrication strategies, such as freeform reversible
[8]
embedding of suspended hydrogels printing . These directly; therefore, the bioprinted constructs were limited
biofabrication approaches present several advantages in long-term culture time or increased thickness despite
as they are compatible with an extensive plethora of accomplishing the fabrication of multi-layered constructs.
However, indirect EBB has already been explored for
scaffolding materials and cells . However, the inherent
[9]
complexity in the three-dimensional (3D) biofabrication bioprinting vascular models, which consists of using
of structures like real-scale organs still poses several fugitive or sacrificial inks. These inks are ejected in the form
challenges which could be overcome by incorporating of solid tubular structures, followed by other hydrogels as
alternative elements such as molds and supports during layers are formed in the adjacent bulk. The sacrificial ink
the 3D bioprinting process. Hence, the integration of is then removed by dissolution, leaving behind a hollow
support structures during the biofabrication process of 3D construct in the gel.
bioprinted structures can be exploited. According to Janarthanan et al., printing self-supported
A noteworthy example of 3D bioprinting using the aid multi-layered constructs with biocompatible hydrogels is
of molds could be the Method A of CoraPrint developed by considered one of the major challenges in extrusion-based
[12]
Albalawi et al. . It is a molding process, which consists of 3D bioprinting . Bioinks must have sufficient mechanical
[10]
the scanning of a live coral, modification of its 3D geometry, stability in soft tissue and organ regeneration post-
3D printing of the coral skeleton with commercial polylactic printing. Furthermore, there are many issues besides post-
acid filament, and creating a silicone mold for Calcium printing stability that include cell damage, porosity with
Carbonate Photoinitiated ink. The time from start to finish interconnected microporous structures, and cross-linking
for the molding process is approximately 4-5 h, excluding density. By overcoming these issues, the capability of cell
the printing time needed for the positive mold model and migration as well as the fine-tuning of their rheological and
the post-molding curing time, which both are dependent swelling properties can be achieved. In addition, it is very
on the desired size of the coral structure. The efficiency of important to ensure that the bioinks used in 3D bioprinting
this method was confirmed in model coral models of out are highly biocompatible in order to accommodate
plant size and thus indicate the possibility of the creation of living cells and to be mechanically stable post-printing.
coral replicas at an efficient rate for large-scale production. Furthermore, these inks require a high level of resolution
Once created, a mold can be used several times and during printing [13,14] . On the other hand, the impact of
subsequent structures can be molded within 10 min. In bioink viscosity on 3D printing and the results revealed
regard to different coral species with varying structural that viscosity and printing speed are interdependent by
geometry and size, this method offers a solution in terms applying pressure to obtain a high level of stability of the
of support and definition. The molding can support the printed structure . Furthermore, other results indicate
[15]
structures of field deployment size while the first step of that there are enhancements in the mechanical properties
3D printing can preserve the sophisticated geometries of of the printed constructs as well as high stability post-
[16]
the coral. Another advantage mentioned is the lack of use printing . However, this study showed a slight decrease
of a large infrastructure setup for transportation since the in cell viability post-printing when examined with human
molds can be smoothly transported to various locations. mesenchymal stem cells (MSC).
Another example of molds used in bioprinting is Regarding bioinks, aromatic and non-aromatic tetra-
perfusable conducts . The mold fabricated was composed peptide amphiphiles, Ac-Ile-Ile-Phe-Lys-NH 2 (IIFK),
[11]
of Polydimethylsiloxane elastomer and a Pluronic F127/ Ac-Ile-Ile-Cha-Lys-NH (IIZK), and Ac-Ile-Cha-Cha-Lys-
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Volume 1 Issue 1 (2022) 2 https://doi.org/10.18063/msam.v1i1.7