A chemically crosslinked biodegradable hydrogel was prepared via a macromer technique, and physicochemical characterizations associated with its potential application as an injectable biomaterial were carried out. The macromers were composed of poly(ethylene glycol) extended with oligomers of biodegradable polyesters such as oligolactide and end-capped with acryloyl groups. Hydrogels were obtained through the polymerization of the macromer aqueous solutions in phosphate-buffered saline initiated by a redox initiator system at body temperature. The initiator system was composed of ammonium persulfate as an initiator and N,NN',N'-tetramethylethylene diamine as an accelerator. The modulus of this chemical gel was much higher than that of a Pluronic physical gel. In vitro biodegradation was also confirmed. The degradation rates were highly tunable by the adjustment of several factors, such as the kind of ester group, the block length of the oligoester, and even the concentration of the accelerator used in the crosslinking reaction. The gelation time could be adjusted to meet the requirements of an injectable biomaterial. The effect of the polymerization heat seemed not to be significant. This kind of biodegradable hydrogel might be in situ formed after being injected into the body and shows potential applications as a unique tissue engineering material free of porogening techniques in scaffold fabrication and less invasive in implantation.(c) 2005 Wiley Periodicals, Inc.