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International Journal of Bioprinting Tunable GelMA-based bioinks for keloid modeling

The damping factor (tan δ), defined as G˝/Gʹ, Rheological analysis demonstrated improved
decreased in the G5A1M1R1 group (Figure 3G), indicating viscoelasticity in the higher MC concentration group,
reduced viscous dissipation and a more dominant elastic though the changes were not statistically significant
component. This aligns with previous studies suggesting (Figure 4C–G). The increase in Gʹ and G˝ suggests that
that gelatin–alginate hydrogels with tan δ values between MC modulates the hydrogel’s mechanical response under
0.25 and 0.45 yield optimal print fidelity. Interestingly, deformation. Unlike previous reports that have described
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mechanical testing revealed slightly higher toughness a Newtonian plateau at low to intermediate shear rates
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in the lower alginate concentration group (Figure 3H, in MC-only solutions, our composite formulation
Table S5). This may be attributed to more efficient exhibited continuous shear-thinning behavior across all
integration of alginate into the polymer matrix at lower shear rates. This likely results from the combined effects
concentrations, enhancing the load distribution within of GelMA, alginate, and laponite-RDS, which modify the
the hydrogel network. Although the difference in Young’s microstructural dynamics of the hydrogel network.
modulus between groups was not statistically significant The 1% MC formulation also demonstrated enhanced
(Figure 3I), a slight increase was observed with higher mechanical integrity, as shown by a steeper stress–strain
alginate content, consistent with steric hindrance and curve (Figure 4H) and improved toughness (Table S5).
chain entanglement effects. Moreover, the elastic modulus increased from 5.53 ± 1.03
kPa (G5A1M0.5R1) to 7.91 ± 1.26 kPa (G5A1M1R1), a
In the absence of ionic crosslinkers, alginate’s influence 1.4-fold enhancement (Figure 4I). These improvements
appears to arise primarily from physical entanglement reflect the role of MC in reinforcing the hydrogel network
with GelMA and MC chains, rather than stable ionic and increasing resistance to deformation. In addition,
or covalent interactions. This physical contribution the degradation rate was slower in the higher MC group
nonetheless improved the structural fidelity and reduced (Figure S1C), which is consistent with MC-induced
the degradation rate of the hydrogel, likely by shielding steric hindrance that reduces enzymatic accessibility to
gelatin cleavage sites from enzymatic degradation cleavage sites.
(Figure S1C). Bioprinting trials demonstrated that However, increased MC concentration could reduce
incorporating 1% alginate, along with GelMA, MC, and the printability (Figure 4K) as the MC controlled shape
laponite-RDS, enabled the formation of robust, well- fidelity and reduced spreading observed in the 1% MC
defined structures at 25°C (Figure 3J), producing better group (Figure 4J). The combination of MC with alginate
printability properties (Figure 3K). These results confirm and GelMA allows for controlled deposition of even low-
that alginate serves as an effective viscosity and elasticity viscosity formulations by modulating the composite’s
enhancer, contributing to the mechanical performance, viscoelastic response. Furthermore, MC is known to alter
printability, and biological utility of the GxAxMxRx the hydrogel’s microstructure and act as a rheological
bioink formulation. modifier, thereby slowing release rates and improving
long-term stability. Overall, increasing MC concentration
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3.3. Enhancing viscosity by methylcellulose enhanced viscosity, mechanical stiffness, and structural
One of the key limitations in extrusion-based bioprinting integrity, without compromising biocompatibility. The
is the need to balance high-resolution printing with addition of MC also increased the loss modulus and
minimal shear-induced cellular damage. MC, a hydrophilic yield stress of the hydrogel blend, contributing to the
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cellulose derivative, is widely used to increase viscosity robustness of printed constructs—especially when fine
and improve print fidelity while supporting cell viability. structural features and cell protection during printing
To evaluate the role of MC in our bioink system, we are required.
compared two concentrations—0.5% (G5A1M0.5R1)
and 1% (G5A1M1R1)—while maintaining constant 3.4. Laponite-RDS controls rheological properties
concentrations of GelMA, alginate, and laponite-RDS Rapid degradation of hydrogels remains a key limitation
(Figure 4A). for long-term applications in tissue engineering. To address
this, laponite-RDS—a synthetic, discotic nanoclay—was
Although increasing the MC concentration led to a incorporated into the bioink formulation to enhance
33% increase in viscosity, this enhancement was modest rheological and mechanical properties. Laponite-RDS
compared to that observed with alginate (Figure 4B). Both consists of alternating silicate layers with embedded
formulations retained a clear shear-thinning profile, which magnesium and lithium ions, forming a charged, plate-like
is critical for facilitating bioink flow during extrusion and structure (~15 nm in diameter, ~1 nm in thickness) that
maintaining structural integrity post-deposition. imparts thixotropic behavior and high surface reactivity.
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Volume 11 Issue 4 (2025) 453 doi: 10.36922/IJB025160154