Photocrosslinked bovine serum albumin hydrogels with partial retention of esterase activity

Novel biohybrid hydrogels based on bovine serum albumin (BSA) were synthesized by one-pot photopolymerization of chemically modified protein in the presence of N,N'-methylenebisacrylamide (MBA) as cross-linking agent under mild conditions. Two batches of methacrylated albumins were prepared by treating the protein with different amounts of methacrylic anhydride (MAN) and the degree of substitution (DS) of primary amines was quantified via trinitrobenzesulfonic acid (TNBS) colorimetric assay. Hydrogels readily formed when a diluted buffered solution of the modified protein and MBA was exposed to LW-UV in the presence of 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one (Irgacure 2959) as the radical initiator. In contrast, no hydrogel was obtained in the absence of a polymerizable BSA, nor when the cross-linker, the radical initiator or UV light exposure was excluded from the reaction, suggesting the critical importance of the combined conditions for hydrogel formation. Hydrogels were characterized via scanning electron microscopy (SEM) and the swelling ratios were monitored at different pHs. The esterolytic activity of the novel biohybrid materials was quantitatively investigated via UV-vis spectroscopy by measuring the release of para-nitrophenol upon incubation with para-nitrophenyl acetate (p-NPA) substrate. The effect of the addition of acrylic acid co-monomer and of the monomer concentration in the catalytic activity and in the swelling behavior was also examined. Finally, the reusability of the materials following one round of catalysis was evaluated.