## 1 Introduction  
Developments in the field of tissue engineering give impetus to the creation of new biomaterials that can be used to repair damaged tissues such as bone, muscle, skin, cartilage, the liver, and the heart [1; 2; 3]. Biopolymers used for tissue engineering should comply with the following requirements: high biodegradability, non-toxicity, porosity for cell attachment and proliferation, mechanical resistance to the pressure created by tissue, and the ability to mimic the damaged tissue [4; 5]. Biomaterials can be synthesized using various techniques, such as electrospinning and 3D printing. Among those, cryopolymerization is a unique method and has several advantages over other methods. A porous structure can be produced by cryo-freezing with the controllable size and volume of the pores that can be adjusted by changing the temperature and the concentration of the starting monomers or prepolymers. The advantage of using cryogels over conventional nano/mesoporous hydrogels is their well-developed 3D porous structure, consisting mainly of open pores, which can be used as a scaffold and carrier of cells [6; 7; 8; 9; 10]. The synthesis of materials at low temperatures provides cryogels with large pores (up to 200 nm) with a spongy and elastic morphology [6; 7; 8; 9]. The stage of cryogel polymerization occurs through two main mechanisms: chemical or physical [7; 8; 9; 11; 12]. Chemically crosslinked cryogels can be obtained by covalent crosslinking of monomers or prepolymers with the aid of crosslinking agents [13; 14]. These bonds have a higher binding energy and, therefore, provide better stability of the chemical interaction between polymer macromolecules due to crosslinking agents [15; 16]. Physically crosslinked cryogels are formed due to ionic/hydrophobic interactions between polymer chains, creating polyelectrolyte complexes (PECs) [3; 8; 17; 18; 19; 20; 21]. Synthetic and natural polymers are used as polymers for tissue engineering. Synthetic polymers such as poly (lactic acid) (PLA), poly (lactic-co-glycolide) (PLGA), poly (\(\varepsilon\)-caprolactone) (PCL), and polyethylene glycol (PEG) are widely used as carriers for peptides, drugs, genes, proteins, and so on due to high mechanical strength and biocompatibility [22; 23; 24]. Natural polymers, due to the presence of certain segments that contribute to an additional therapeutic effect during tissue regeneration, are also widely employed for biomedical applications. Due to their superior biocompatibility, negative immunological influence, elastic and diffusive properties, and low toxicity, natural polymers such as collagen, chitosan, alginate, silk, fucoidan, elastin, gelatin, and hyaluronic acid are extensively used in tissue engineering [25; 26; 27; 28]. Gelatin (Gel) is a biopolymer derived from animal collagen. It is a cheap, biocompatible, biodegradable, non-immunogenic biopolymer widely used in clinical applications [29]. In terms of chemical composition, gelatin is close to collagen. However, unlike collagen, gelatin, whose macromolecules do not have an ordered structure, is soluble in water, which makes it a convenient material for the preparation of initial gel-forming systems for the formation of cryogels or cryostructures [30; 31]. Chitosan (Ch), a naturally occurring unsulfated glycosaminoglycan (GAG), is a linear polysaccharide that is a part of the extracellular matrix (ECM), consisting of \(\beta\) (1\(\rightarrow\)4) linked D-glucosamine residues with a variable number of randomly located n-acetyl-glucosamine groups [32; 33]. Chitosan (Ch) has excellent biocompatibility, biodegradability, non-toxicity, adsorptive properties, and degradability by lysozyme, a natural enzyme [34]. Chondroitin sulfate (CS) is a sulfated polysaccharide in C4 or C6 of its repeating unit, containing GAG and galactosamine [35]. CS attaches to proteins as part of proteoglycan, an important component of cartilage, and its inclusion in a scaffold allows for the secretion of proteoglycans and type II collagen [36].