Thermoresponsive hydrogels from BSA esterified with low molecular weight PEG

Bovine serum albumin (BSA) and low molecular weight polyethylene glycol (PEG) were reacted in a single‐step reaction to synthesize translucent hydrogels with a sol–gel transition at temperatures between 37 and 40°C. Gelation occurred by aggregation of smaller assemblies of BSA–PEG precursors within minutes. The sol–gel transition concentration depended on the molecular weight of PEG only at temperatures below 35°C; above 45°C phase separation occurred and a precipitate formed. Microscopic examination showed the porous structure of the gels. At a fairly low grafting ratio, BSA preserved its native secondary and tertiary structure and maintained its capability for binding and enclosing small molecules. Drug delivery was assessed by a discontinuous method in vitro using 5‐fluorouracil. Degradation tests with trypsin confirmed that the hydrogels were biodegradable. This novel material holds promise for biomedical applications as potentially injectable drug delivery vehicle.