Production and characterization of alginate-silk fibroin based hydrogel and cryogel for bone tissue engineering

Bone tissue engineering is a multidisciplinary field that offers alternative solutions to the limitations and complications of autologous and allogeneic grafts. The primary objective of this field is to develop tissue scaffolds that provide biologically, mechanically, and structurally appropriate properties for the target tissue, thereby contributing to the treatment of clinical conditions such as bone fractures, tissue loss, and bone cancer. To this end, three-dimensional and porous structures that mimic the natural bone extracellular matrix are designed using natural or synthetic biopolymers. These scaffolds are expected to be biocompatible to support cell adhesion and proliferation, exhibit sufficient mechanical strength to withstand physiological stresses, and facilitate osteogenesis. In this thesis, hydrogel and cryogel systems were developed using alginate, oxidized alginate, silk fibroin, and hydroxyapatite at varying concentrations for bone tissue engineering applications. Two different calcium chloride (CaCl₂) concentrations (0.1 M and 0.3 M) were used as crosslinking agents. Within the scope of characterization, viscosity analyses were performed, and all groups exhibited shear-thinning behavior. The viscosity significantly increased with increasing HAp content, which was attributed to hydroxyapatite acting as a physical filler that limited the mobility of polymer chains. This shear-thinning behavior improves the processability of the materials in applications such as 3D printing and injection molding. In addition, the viscoelastic properties of the systems were evaluated through frequency sweep tests. The storage modulus (G') values were found to be higher in cryogel systems, indicating dominant elastic behavior. The relationship G' > G'' was observed in both hydrogel and cryogel samples, confirming their viscoelastic solid characteristics. The swelling behavior of the scaffolds was also comparatively assessed. The ability of a scaffold to retain fluid is critically important for nutrient transport and waste removal in tissue environments. Cryogels exhibited higher swelling ratios than hydrogels, which can be attributed to their more porous and interconnected structure, allowing for greater fluid uptake.