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International Journal of Bioprinting 3D-printed variable stiffness scaffolds

material compositions may be used to promote region- At D21, samples containing HAMA had the greatest
dependent collagen synthesis similar to the native tissue. mechanical properties compared to the other groups,
with the highest compressive modulus at 0.36 MPa and
3.8. Mechanical properties of cell-seeded equilibrium modulus at 0.26 MPa. It was reported that
hybrid scaffolds sGAGs attract water within the meniscus tissue. This
Mechanical properties are crucial for the success water uptake and collagen fiber orientation are known to
of biomaterials in tissue engineering. A decrease in have a symbiotic relationship concerning the compressive
mechanical properties indicates the dissolution of the properties of the tissue. In this study, all groups exhibited
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hydrogel, suggesting a loss of structural integrity. However, an increase in compressive properties, accompanied by
an increase in mechanical properties over time may be an overall reduction in sGAGs from D1 in both GelMA/
an indication of ECM production. In this study, no CS/HA and GelMA/CS/HAMA groups. Therefore,
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significant degradation was observed, and all constructs it is hypothesized that the sGAG level does not fully
were easy to handle at D21. The addition of CS/HA to the account for the changes in compressive properties, but
GelMA matrix on D1 caused a decrease in the equilibrium rather the location-specific distribution of GAGs plays a
and compressive modulus (Figure 10A and B). This significant role. From histological analysis, it is evident
decrease is likely due to a reduction in crosslink density that newly secreted ECM is concentrated along the PCL
caused by GAG molecules hindering the crosslinking of fiber, potentially resulting in narrower spaces between
GelMA. Conversely, the addition of HAMA increased the fibers. This may restrict water flow and mimic the
the equilibrium and compressive modulus. Moreover, the natural synergetic relationship between the collagen fibers
addition of HAMA enhanced the hydrogel’s mechanical and GAGs in natural tissue. Furthermore, GelMA/CS/
properties compared to GelMA alone or with the addition HA exhibited the most significant change in mechanical
of unmethacrylated HA. This improvement could be properties compared to GelMA/CS/HAMA during cell
attributed to the increased crosslink density of the matrix, culture, with the compressive modulus increasing by 41%
with HAMA concurrently crosslinked along with the between D1 and D21. The initial mechanical properties
GelMA. The different degradation characteristics of the are dependent on the crosslink density of the polymer
hydrogels containing HA and HAMA provide insight into network, and a lower crosslink density facilitates diffusion
their crosslinking mechanisms. For instance, the GelMA/ of the newly secreted matrix. Therefore, hydrogels that are
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CS/HA hydrogel completely digests in papain. However, initially stiff may hinder the formation and distribution of
for GelMA/CS/HAMA, when the gelatin component of a ECM, while softer materials facilitate new ECM infiltration,
gel is removed by papain, an intact and stable network of consequently becoming stiffer after in vitro culture. 63,64 The
crosslinked HAMA remains. The existence of this stable same trend is observed here, whereby the HA group features
HAMA network indicates that an interpenetrating HAMA enhanced mechanical properties; however, interestingly,
network exists within the bulk GelMA network, which both HA and HAMA groups have similar collagen and
explains the significantly higher equilibrium modulus in GAG content. Therefore, this change in mechanical
constructs containing HAMA compared to the HA at D1. properties may be explained not only by the production of
Additionally, after one day in culture media, the wet weight the matrix, but also by the interaction of molecules within
of constructs containing HA was greater than GelMA the ECM. It is expected that a higher interaction between
alone and constructs containing HAMA (Figure 10C). This the unmethacrylated HA with the newly produced ECM
is attributed to a reduction in crosslink density, thereby compared to HAMA enables the retention of molecules
enabling more water uptake. During culture, the hydrogel within the matrix when a compressive load is applied.
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scaffolds were subjected to enzymatic degradation. As the With longer in vitro culture, more distinct changes in
hydrogels are GelMA-based, the presence of cells may mechanical properties would likely be observed between
result in rapid degradation of the hydrogel via matrix the groups. Both the equilibrium and compressive
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metalloproteinases (MMP) activity. After 21 days of moduli of hydrogels alone were found to be lower than
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culture, both the compressive and equilibrium modulus the native meniscal tissue. However, this is mitigated by
increased in all groups. This change in mechanical the reinforcement of hydrogels with PCL, which provides
properties is a result of a balance between the production structural integrity to the scaffolds. The observed changes
of new ECM and hydrolytic degradation of the hydrogel.
Therefore, the enhanced mechanical properties are a in mechanical properties of hydrogels over time in the in
result of the cell-laden matrix. Additionally, there was no vitro cell culture study are indicative of cell proliferation
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significant change in wet weight within each group over and ECM production.
time (Figure 10C), suggesting that the rate of degradation From these results, GelMA/CS/HAMA is suggested as
of the gel matched the rate of new matrix production. a possible candidate for the peripheral region of the full

Volume 10 Issue 4 (2024) 510 doi: 10.36922/ijb.3784