Tethering drug substances to a gel network is an effective way of controlling the release kinetics of hydrogel-based drug delivery systems. Here, we report on in situ forming, biodegradable hydrogels that allow for the covalent attachment of peptides or proteins. Hydrogels were prepared by step-growth polymerization of branched poly(ethylene glycol). The gel strength ranged from 1075 to 2435 Pa; the degradation time varied between 24 and 120 h. Fluorescence recovery after photobleaching showed that fluorescently labeled bovine serum albumin (FITC-BSA) was successfully bound to the gel network during gel formation. Within 168 h. the mobility of the tethered molecules gradually increased due to polymer degradation. Using FITC-BSA and lysozyme as model proteins, we showed the potential of the developed hydrogels for time-controlled release. The obtained release profiles had a sigmoidal shape and matched the degradation profile very well; protein release was complete after 96 h.
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