Macromers having a polyethylene glycol) central block, extended with oligomers of a-hydroxy acids such as oligo (dMactic acid) or oligo (glycolic acid) and terminated with acrylate groups, were synthesized and characterized with the goal of obtaining a bioerodible hydrogel that could be formed in direct contact with tissues or proteins by photopolymerization of aqueous solutions of the macromer. It was determined that the PEG component of these macromers must be greater than approximately 55 mol% to provide water solubility. The amphiphilic nature of the macromers causes them to assume a micellar conformation, which enables them to undergo rapid photopolymerization. Due to the multifunctionality of the macromers, polymerization results in the formation of cross-linked gels. These gels degradeupon hydrolysisof the oligo (a-hydroxy acid) regions into polyethylene glycol), the-hydroxy acid, and oligo (acrylic acid). The degradation rates of thesegels can be tailored by appropriate choice of the oligo (a-hydroxy acid) from less than 1 day to up to 4 months. Using nontoxic photoinitiators, the macromers can be rapidly photopolymerized with visible light in direct contact with tissues without excess heating or local toxicity. If polymerized in contact with tissues, the gels adhere to thetissues, presumably by interpenetration; if polymerized prior to contact with tissues, the gels are very nonadhesive, presumably by possession of a large amountof free water which is not hydrogen bonded with the ether linkages of the ethylene glycol mere. These novel materials are suitable for a number of biomedical applications andshow potential for use in macromolecular drug delivery.