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Abstract
Biosynthetic hydrogels which have tailorable physical properties as well as the desired biological attributes to support cellular interaction have emerged as potential biomaterials for cell encapsulation. These hydrogels are normally fabricated by incorporating biological molecules into a synthetic hydrogel network. However, long term use of these matrices requires the biological molecules to be covalently bound into the network. This stable integration can be achieved by chemically modifying the biological molecules with short linear polymer chains, such as poly(ethylene glycol) (PEG), or functional moieties like acrylate and methacrylates. However, these chemical functionalisation processes may impose degradation and denaturation of the biological molecules, as well as disrupting the bioactive side groups that are required for cellular interactions.Therefore, the overall aim of this research is to covalently incorporate biological molecules into synthetic hydrogels without the need of prior chemical modification. A visible light polymerisation system consisting of ruthenium and persulphate that was previously shown to crosslink proteins through their phenolic residues was employed. It was shown that by grafting phenolic containing moieties, such as tyramine onto poly(vinyl alcohol) (PVA-Tyr), the resultant PVA-Tyr was able to be crosslinked in a similar manner to proteins using the ruthenium/persulphate system. The physical properties of the hydrogels were tailorable through varying the nominal macromer concentration. Non-chemically modified gelatin was successfully covalently integrated into the PVA-Tyr hydrogels, without affecting the base characteristics (mass loss, swelling and degradation profile) of PVA-Tyr, but also retained the bioactivity to support cells in 2D culture (fibroblasts, endothelial, Schwann cells). Fibroblasts were also encapsulated inside the PVA-Tyr gels, where it was showed that the presence of the antioxidative protein, sericin was needed to ensure survival of the cells during the photoencapsulation process. However, both sericin and gelatin were required synergistically to facilitate long-term 3D cell growth, proliferation and function. The encapsulated cells were able to form clusters and interconnected networks, as well as remained metabolically active after 21 days in culture. This work has demonstrated a novel method to covalently incorporate proteins in their native state into synthetic hydrogels. The resultant PVA-Tyr/protein biosynthetic hydrogels showed great promise as tissue engineering matrices.