Novel degradable poly(ethylene glycol) hydrogels for controlled release of protein.

Hydrogels have become increasingly important in the biomedical field. This paper describes synthesis and characterization of two types of novel degradable poly(ethylene glycol) (PEG) hydrogels with potential utility as delivery carriers for bioactive drugs. The simplest gel is prepared by one-step polycondensation of difunctional PEG acid and branched PEG "polyol". The second type of the novel degradable PEG hydrogel was prepared in a two-step process, in which an ester-containing, amine-reactive PEG derivative was synthesized and then reacted with a branched PEG amine to form the gel. The two-step gels are formed in very mild conditions, and therefore fragile drugs such as proteins can be loaded during gel formation. Because most proteins have free amino groups in the sequence, these proteins can be covalently linked to the hydrogel network. This covalent attachment provides a new way to achieve long-term controlled release of proteins. These hydrogels have a wide range of degradation rates. Upon hydrolysis, these PEG hydrogels will degrade into low molecular weight PEG derivatives, which can be easily cleared by the body.