## 4 Discussion  
Different methods of scaffold design can be used to manipulate the mechanical properties of hydrogel scaffolds to achieve properties that are best suited for cell support. Various studies have shown that the mechanical properties of scaffolds must be carefully controlled to successfully simulate the extracellular matrix that supports cells in human tissue. This is because there is a dynamic relationship between cell growth and viability and the extracellular matrix [25; 31; 32; 33; 34]. These experiments have shown that the water retention rate, elasticity, and degradation rate of a hydrogel construct can, to some extent, be controlled by changing the material composition of the scaffold. In this study, hydrogels containing alginate-gelatin showed a higher water retention capacity than the pure alginate gels. One possible explanation for this observation was that pure alginate molecules experienced stronger intermolecular forces with one another compared to when they were part of hybrid hydrogels. Adding gelatin or MC may interfere with the intermolecular forces between adjacent alginate molecules, and as a result, the attraction between the alginate molecules and surrounding water molecules may be stronger than in pure alginate hydrogels. This leads to greater water absorption. Furthermore, the melting point of gelatin is about 35 \({}^{\circ}\)C [35]; therefore, at 37 \({}^{\circ}\)C gelatin would be in liquid form, and as a result, there would be gaps in the scaffold which would be replaced by the surrounding water molecules. This result would lead to a higher absorption rate when compared to a pure alginate hydrogel sample. This high water retention capacity allows cells to readily exchange important molecules such as ions and signaling molecules with their environment [25]. Additionally, hybrid hydrogels containing gelatin had a lower elastic modulus compared to alginate-MC hybrid hydrogels, possibly because of the degradation of gelatin at physiological temperatures. The decomposition of gelatin due to its melting point of around 35 \({}^{\circ}\)C would cause the formation of gaps in the construct, and this could compromise its mechanical stability and result in a lower elastic modulus. These results indicated that hydrogels could be constructed with different materials depending on the degree of stiffness necessary for the tissue type that requires regeneration. This outcome allows for better specificity and control in scaffold design and construction. Notably, in future studies, water syneresis can be evaluated to consider the effect of shrinkage. Group 3 showed the highest percentage of degradation in comparison to the other hydrogels. MC is soluble in water at temperatures lower than 40-50 \({}^{\circ}\)C, as mentioned earlier, and it has a melting point of about 35 \({}^{\circ}\)C [35; 36]. The weakened intermolecular interactions of MC and gelatin at physiological temperatures would, therefore, lead to a high rate of degradation of this gel over time. Here, we proposed some compositions with various mechanical and swelling/degradation rates. Our results also showed different flow behaviors from Newtonian to non-Newtonian ones. Group 1, having the highest viscosity, showed good printability discussed later on. It meant that the more viscous the biomaterial, the more appropriate printability could be achieved. However, high viscous biomaterials may not printable. Referring back to the mentioned general rule, we recommend an appropriate range of viscosity from 300 to 30,000 cps (0.3-30 PaS). Group 4 was not in the recommended range, which agreed with our printability results so that a poor printability was observed for this group. Notably, as we use lower viscous biomaterials; likewise, higher speeds should be implemented. However, it may cause difficulties in printing, such as sudden direction changes in the edges of scaffolds.