## 3 Results and Discussion
All the cryogels exhibited a macroporous structure consisting of pores having different shapes and sizes. The average pore sizes of the cryogels significantly changed depending on the CS concentration. For instance, they were 123 \(\pm\) 75, 174 \(\pm\) 68, 230 \(\pm\) 76, 217 \(\pm\) 124, and 185 \(\pm\) 83 \(\upmu\)m for GelChCS10, GelChCS25, GelChCS50, GelChCS100, and GelChCS250, respectively. The GelChCS100 sample had pores above 500 \(\upmu\)m, which does not allow MSC cells to proliferate directly onto the polymer, since the cells may not attach to the cryogel. The GelChCS50 and GelChCS100 samples had sufficient pores. The pores on the surface of the GelChCS50 cryogel were evenly distributed and may be sufficient for chondrogenic differentiation, since the largest pore size accommodates more cells that can agglomerate. The TG/DTA results of the scaffolds together with the control scaffold without chemical crosslinking are shown in Figure 5. TG curves show the weight loss of the samples in the temperature ranges of 30-100 \({}^{\circ}\)C and 200-500 \({}^{\circ}\)C. The weight loss at low temperature (<100 \({}^{\circ}\)C) is due to the loss of water in the samples. It is known that at 40-60 \({}^{\circ}\)C and 80-120 \({}^{\circ}\)C, free water and water bound with hydrogen bonds are released, respectively [47]. At higher temperatures until 160 \({}^{\circ}\)C, water molecules more strongly linked through polar interactions with carboxylate groups are released [42]. At the high temperature range (200-500 \({}^{\circ}\)C), an average weight loss of 60% of the substance occurred, which corresponds to the thermal and oxidative decomposition of the cryogel components. The decomposition of the control sample occurred at 110 \({}^{\circ}\)C, reaching a maximum at 270 \({}^{\circ}\)C, while in  
Figure 4: Biodegradation behavior of the cryogels in PBS at 37 \({}^{\circ}\)C for 8 weeks. other cryogels, decomposition occurred on average from 200 \({}^{\circ}\)C and decomposed to the maximum at 280-311 \({}^{\circ}\)C; this confirms the formation of chemical crosslinks between the functional groups of gelatin, chitosan, and chondro sulfate with EDC. Upon reaching the final temperature, the weight losses became 80, 78, 79, 81, and 82% for GelChCS10, GelChCS25, GelChCS50, GelChCS100, and GelChCS250, respectively, as compared to 95% for the control sample. The DSC thermograms of the cryogels show an endothermic peak up to 100 \({}^{\circ}\)C that is seen for all cryogels, which corresponds to the release of residual water. Moreover, the glass transition temperature T\({}_{\rm g}\) of the cryogels was 354, 591, 443, 389, and 397 \({}^{\circ}\)C for GelChCS10, GelChCS25, GelChCS50, GelChCS100, and GelChCS250, respectively, as compared to 291 \({}^{\circ}\)C for the control sample. This also demonstrates the formation of more stable structures between the polymer chains in the cryogel network due to the chemical crosslinks in the cryogels. The MTT assay gives information regarding metabolic activity and proliferative capacity of cells seeded on a scaffold which differ by variated concentrations of chondro-6-sulfate (Figure 6). The maximal concentration (100%) was equal to 1000 \(\rm\mu g\) of GelChCS dissolved in 1 mL of media, sequentially, 50%-500 \(\rm\mu g/mL\), 25%-250 \(\rm\mu g/mL\), 12.25%-122.5 \(\rm\mu g/mL\), 6.25%-62.5 \(\rm\mu g/mL\), 3.1%-31.3 \(\rm\mu g/mL\), 1.56%-15.6 \(\rm\mu g/mL\), and 0.78%-7.8 \(\rm\mu g/mL\). According to the obtained data, the cells cultivated in media with the titated GelChCS50 extract showed a higher ability to proliferate, while for GelChCS250 the same concentrations induce inhibition of cell growth. Also, IC50 was determined for each scaffold: GelChCS10-24.11 \(\rm\mu g/mL\), GelChCS25-88.48 \(\rm\mu g/mL\), GeChCS50-275.8 \(\rm\mu g/mL\), GeChCS100-111.7 \(\rm\mu g/mL\), and GelChCS250-7.257 \(\rm\mu g/mL\). It can be seen that the GelChCS50 scaffold has the highest maximum permissible concentration and is suitable for cell cultivation. Figure 5: TG/DTG/DSC curves of the cryogels.