## 3 Results and Discussion
Based on the results obtained, it can be concluded that the cryogels have rather favorable properties for their use as a carrier and for cell proliferation. The swelling capacity of polymers is inherent in biomedical applications and tissue engineering. The swelling capacity of polymers makes it possible to use them in drug delivery systems [53]. The equilibrium swelling ratio of the cryogels was determined in PBS (pH 7.4) at 37 \({}^{\circ}\)C after an immersion time of 24 h, while at longer times, they started to biodegrade. The results showed that the samples GelChCS10, GelChCS25, and GelChCS50 had the highest swelling ratios of around 12 as compared to other cryogels (the data points at time = 1 h in Figure 3). Apparently, with increasing CS concentration, more porous polymer networks are formed, which provide the greatest swelling ability. However, the GelChCS10 and GelChCS25 cryogels were less stable and degraded over time. The cryogels GelChCS100 and GelChCS250 ha closed and large pore morphologies (SEM results are shown below), which cannot swell like previous cryogels. The biodegradation of polymers also plays an important role in their use in tissue engineering. Partial degradation makes it possible to use the polymer for a longer time as a carrier of cells without additional implantation of the biomaterial into the studied healing site. The lower the degree of biodegradation, the longer the period of time the polymer can be used to deliver a biological object, such as drugs and cells. Thus, we investigated the degradation of the cryogel matrices GelChCS10, GelChCS25, GelChCS50, GelChCS100, and GelChCS250 in a sterile solution of 0.1 M of PBS (pH 7.4) at 37 \({}^{\circ}\)C under sterile conditions for 8 weeks. The in vitro decomposition rate of the cryogels was \(58\pm 2.5\), \(55\pm 3.5\), \(40\pm 2.1\), \(43\pm 2.5\), and \(81\pm 1.6\%\) for GelChCS10, GelChCS25, GelChCS50, GelChCS100, and GelChCS250, respectively (Figure 4). During biodegradation, polymer chains forming the pore walls of the cryogels break down into low-molecular weight polymers, and thereby they dissolve in the solvent and lead to weight loss. The presence of water-soluble gelatin in the present cryogels provided an additional hydrophilicity and enhances biodegradation. As seen from Figure 4, GelChCS50 and GelChCS100 cryogels had the lowest degree of degradation which is likely due to the larger number of covalent bonds between Gel, Ch, and CS via the EDC crosslink. In contrast, the GelChCS250 sample lost its shape after a week in PBS and exhibited the maximum degree of degradation. Apparently, the excessive amount of CS anionic groups does not create conditions for covalent crosslinking with EDC so that weakly crosslinked  
Figure 3: Dependence of the swelling capacity of the cryogels in PBS at 37 \({}^{\circ}\)C at the time of swelling. polymer chains are formed, thereby destroying intermolecular chains inside the cryogel. It is assumed that with an excess of CS, a large number of unreacted chains is formed, which makes the cryogel unstable. On week 6, visual observation showed that the GelChCS10 and GelChCS25 samples had also lost their original shapes. These results suggest that weakly crosslinked polymer chains are formed in the samples, which are unable to withstand the effect of PBS (pH 7.4) at long times. An increased biodegradation of polymers with increasing CS concentration was also reported in the literature [24]. Pore size and shape play an important role in tissue engineering scaffolds. The pores provide intercellular contact between cells, showing higher markers of chondrogenesis, and can be used for the treatment of bone regeneration and in tissue engineering in general. It is known that pores above 500 \(\upmu\)m are the limit for scaffolds, since at a given size, cell infiltration is enhanced instead of promoting cell adhesion to the scaffold [54; 55]. The surface morphology of the synthesized polymers was examined by SEM analysis (Figure S1).