Page 497 - IJB-9-5

International Journal of Bioprinting CECM-GelMA bioinks of DLP 3D printing for corneal engineering

proteins and the microstructure, the chemical stability of Several studies have indicated that growth factors
hydrogels is increased [48-51] . These findings show that the hold the key components that regulate cell fate in the
composite hydrogel has enhanced deformation resistance process of tissue regeneration. The corneal decellularized
and high resilience, making it a viable material for extracellular matrix retains most of the ECM components
prosthetic corneas. of natural tissues , which can be used to 3D print and
[55]
Then, additional crucial characteristics required for embed corneal cells. Counterintuitively, the addition of
artificial corneas were examined. Initially, the in vitro in situ CECM allowed the population of cells retained in the
degradation and collagenase degradation experiments of hydrogels to better mimic the native tissue environment
GelMA and CECM-GelMA hydrogels followed similar rules. compared to pure GelMA. According to Figure 5A, hCFs
The higher degradation rate of the CECM-GelMA hydrogel loaded in the GelMA hydrogels were distributed in the
indicates that it contains segments of collagen peptides bottom layer of the sample after 2 weeks of cultivation.
that are vulnerable to proteases . The incorporation of Due to the durotaxis and mechanosensing of fibroblasts,
[52]
natural corneal extracellular matrix makes the hydrogels the hCFs in the GelMA hydrogel crawled out, reducing
adjust biodegradability. This also indicates that CECM the number of internal cells. However, due to the role of
contains more protein molecules, such as collagen and CECM, the internal environment of the CECM-GelMA
proteoglycans, and has more cleavable sites. However, when hydrogel is more suitable, and the hCFs can survive
PBS is used for in situ degradation, the presence of CECM and spread well in the interior, showing higher cell
reduces the degree of in situ degradation and enhances activity, as shown in Figure 5B. However, the hCFs in the
the stability of the hydrogel against environmental attacks CECM-GelMA hydrogel were cultured and distributed
(Figure 3A and B). Next, in the swelling experiment, the relatively uniformly. It was speculated that this may be
CECM-GelMA hydrogel had a lower swelling rate. This because CECM exhibits its potential to survive cells from
may be due to the fact that the CECM contains biologically endogenous sources through a variety of mechanisms,
active molecules, such as structural proteins and chitosan, including the release of matrix-bound growth factors.
which are cross-wound inside the hydrogel structure and Subsequently, immunofluorescence staining analyses
make the composite hydrogel structure more compact. of essential proteins were carried out to determine the
Therefore, the crosslinked network in the blended hydrogels effects of scaled 3D architectures on cell function, motility,
makes it difficult for water to diffuse. It is revealed that for and differentiation. Lumican is a small leucine-rich
a lower swelling rate, the samples produce less deformation proteoglycans (SLRPs) expressed in the corneal stroma
[56]
(Figure 3C and D). that plays an important role in corneal transparency .
α-SMA is a specific protein of corneal myofibroblasts.
Furthermore, one of the crucial factors is the Studies have shown that reversible transformation
transmittance of the artificial cornea. Upon testing, the between keratocytes and corneal fibroblasts can occur,
transparency of the sample containing 1% (w/v) CECM but if the stimulation is strong enough to transform
was lower than that of pure GelMA (Figure 4). Due to the into myofibroblasts, it is irreversible . The hCFs in the
[57]
blending of CECM, the optical homogeneity decreased, and composite hydrogel displayed upregulated expression of
the light scattering increased. However, compared with the lumican and downregulated expression of α-SMA, while
transmittance of traditionally prepared keratoprostheses the control group showed the opposite (Figure 6). This
containing CECM , which is approximately 50%, the shows that fibroblasts not only survive stably in CECM-
[53]
transmittance of the CECM-GelMA hydrogel can be GelMA hydrogels, but also do not undergo irreversible
stabilized at ~86% in the wavelength range greater than transformation to myofibroblasts and still maintain part
500 nm. Although the CECM-GelMA hydrogel did not of the function of keratocytes. Conversely, in response to
achieve more than 90% light transmittance of the pure such stimuli in GelMA hydrogels, hCFs were transformed
GelMA hydrogel, it still had better light transmittance into myofibroblasts expressing α-SMA .
[58]
than other artificial corneas . Notably, the spectral
[54]
transmittance of the hydrogel changed after 2 weeks of Further research was performed on the impact of a 3D
culture on the hCF-loaded hydrogel (Figure 4B). After complex environment on hCFs. Among them, quiescent
analysis, the result may be due to the vigorous functional keratocytes express ALDH3A1 when they transform
activity of hCFs, with obvious protein synthesis and into corneal fibroblasts or myofibroblasts, which is
secretion activities, which increases the colloidal osmotic accompanied by marked downregulation of ALDH3A1.
pressure of the hCF-loaded samples and plays an important Therefore, in the complex CECM-GelMA surroundings,
role in maintaining the water balance of the samples. With hCFs secreted proteoglycans such as ALDH3A1 (Figure 7),
increasing colloid osmotic pressure, the light transmittance which is similar to resting keratocytes. At the same time,
of the sample is improved to a certain extent. a similar behavior was also revealed in the expression of

Volume 9 Issue 5 (2023) 489 https://doi.org/10.18063/ijb.774