Physicochemical Effects of PEG content in Alginate-based Double Network Hydrogels as Hybrid Scaffolds

Purpose: This study aims to prepare a double-network hydrogels as hybrid networks bearing both natural and synthetic polymers to obtain scaffolds with increased swelling capacity and tunable mechanical and morphological properties. Physically cross-linked alginate hydrogel was reinforced with various ratios of Poly(ethylene glycol) (PEG) polymers which were chemically gellated via UV light exposure with a water soluble initiator. Method: The synthesis methodology involves a sequential crosslinking approach by carefully controlling the reaction parameters to achieve a hybrid structure to mimic the natural tissue extracellular matrix. Physicochemical properties of the resulting hydrogels were systematically investigated via Fourier-transform infrared spectroscopy (FT-IR) for chemical composition and Scanning Electron Microscopy (SEM) for their morphological features like porosity. Furthermore, the effect of PEG amount in the final hydrogel (10, 20 and 40%) on the swelling capacity was evaluated as well as the rheological properties. Results: Prepared double-network hydrogels were demonstrated to be composed of both natural alginate polymer and synthetic PEG chains in FT-IR spectrum. Although 10%PEG containing hydrogel was not significantly different in terms of swelling capacity from the alginate hydrogel alone, increasing PEG amount has an ameliorating effect. Comparative reological studies presented that introducing covalently cross-linked PEG network into alginate one increased crosspoint of storage and loss moduli almost 12 times more providing a stiffer scaffold. Also, increasing PEG content decreased the pore size on SEM images, indicating more crosslinking points in final hydrogel structure. Conclusion: Hybrid double-network hydrogels were successfully prepared by introducing increasing amounts of dimethacrylated PEG chains into the physically cross-linked biocompatible alginate network. Known as its good water solubility, PEG chains were shown to have a better effect on the swelling capacity and mechanical properties of the final hydrogel, together with providing tunable pore size.