Page 126 - IJB-10-2

International Journal of Bioprinting 3D bioprinting for corneal regeneration

composite membranes alongside chitosan and PCL. substances into complex 3D structures. The construction
The resulting hydrated membranes exhibited increased of the scaffolds involves three main steps. Firstly, data
flexibility and ease of handling, with the 50% nanoparticles pertaining to the organs and tissues slated for printing are
and 25% PCL composition demonstrating near collected to facilitate the selection of appropriate models
transparency comparable to the acellular stroma. and materials. Secondly, a computer model is generated
In an effort to improve the properties of chitosan, Ulag based on this data, and the corresponding printing code is
et al. incorporated polyvinyl alcohol (PVA), a widely- written. The final step involves the physical construction of
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used synthetic polymer in biomedicine that is known for the structure through 3D printing.
its utility as a carrier material due to its physio-mechanical During the design and material selection phases, an
properties. Employing an aluminum mold shaped like important consideration is ensuring that the bioprinted
a cornea, the hydrogel was printed using the extrusion scaffold effectively provides the appropriate supply of
method without the use of a cross-linking material. nutrients and oxygen for the diverse cell types encapsulated
Although the prepared composite gel was completely within the hydrogel.
transparent, measured transmittance indicated values
between 49% and 56%. Importantly, the scaffold perfectly These bioprinted tissue models serve as valuable tools
retained the shape of the cornea post-printing. Chen et in elucidating the behavior of immobilized stem cells
al. developed a composite hydrogel using type 1 collagen, within different matrix materials. Examining cell functions
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post-bioprinting yields invaluable insights into the impact
chitosan, and sodium hyaluronate (NaHA). The study
explored the effect of the ratio of individual components of processes during 3D printing on cellular behavior.
on transmittance and water content within the prepared A comprehensive understanding of these dynamics is
hydrogels. Notably, the hydrogels containing 0.5 and 0.9 essential not only for the success of future bioprinting
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(wt)% NaHA exhibited a transmittance of 95%. In vitro endeavors but also for their widespread applications.
cytocompatibility studies and in vivo rabbit experiments
revealed that the hydrogel composed of 20% collagen, 9. Pre-clinical and clinical studies with
10% chitosan, and 0.5% NaHA proved to be the most bioprinted cornea
efficacious, maintaining transparency even 5 months post- Many clinical solutions are currently available to restore
implantation. the epithelial layer of the cornea, and it is even possible
to replace the endothelial layer through endothelial
8. Stem cells in cornea bioprinting keratoplasty (e.g., Descemet stripping endothelial
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There are two main categories of stem cells: embryonic keratoplasty [DSEK]). However, only three therapies
stem cells (ESCs) and adult stem cells. In addition, exist for replacing the stroma, which constitutes about 90%
induced pluripotent stem cells (iPSCs) represent another of the cornea. These options include the transplantation
category created through the dedifferentiation of somatic of the entire cornea from a human donor (penetrating
cells. Adult stem cells include mesenchymal stem keratoplasty), the partial transplantation of the stroma in
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cells, which can be sourced from diverse tissues such as a deeper layer (deep anterior lamellar keratoplasty), or
corneal stroma (CS-MSC), bone marrow (BM-MSC), the transplantation in a less deep layer (anterior lamellar
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adipose tissue (AD-MSC), umbilical cord (UC-MSC), keratoplasty) (Figure 4). However, these surgical
placenta (P-MSC), and dental pulp. Mesenchymal solutions pose a considerable risk of scarring, rejection,
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stem cells exhibit the ability to differentiate into multiple and infection.
cell types under in vitro conditions, such as adipocytes, In recent years, owing to technological advancements,
chondrocytes, osteocytes, and cardiomyocytes. These cells, numerous new techniques have been explored in the
characterized by exceptionally high immune tolerance and quest to develop corneal substitutes, among which 3D
the capacity to exert an anti-inflammatory effect through printing has emerged as a notable contender. The advent
their immunomodulation function, find application in of 3D printing introduces possibilities for regenerative
allografts. This usage serves to reduce the likelihood of medicine and drug testing. Consequently, the growing
rejection and contributes to expedited wound healing. 83,84
interest in personalized medicine finds additional avenues,
The use of stem cells in bioprinting stands as a positioning itself as an excellent model for research. The
widespread practice in regenerative medicine research, application of this technology in ophthalmic contexts
facilitating the production of various implants and tissue holds promise for advancing clinical practices, enriching
models (Figure 3). The 3D printing technique orchestrates medical education, and presenting a cost-effective solution
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the arrangement of cells, multiple factors, and active for corneal transplants. 90

Volume 10 Issue 2 (2024) 118 doi: 10.36922/ijb.1669