Micelle formation and reaction kinetics of a bioabsorbable polyethylene glycol-oligolactide ABA block copolymer hydrogel

Bioabsorbable hydrogels are useful in a variety of medical applications. Water soluble macromers composed of polyethylene glycol (PEG)-oligo(d,l-lactide) ABA block copolymers end-capped with acrylate groups can be photopolymerized on tissue to provide hydrogels. The synthesis, characterization and photopolymerization of these monomers using either ultra-violet or visible light have been reported previously. The size and number of micelles in solution are elements in the optimization of both the extent and rate of polymerization. In the present study, gel modulus and end group analysis methods were used to characterize the degree of conversion of gel formed from macromers having various oligo(d,l-lactide) (A) block lengths. The formation of micelles was studied using dye solubilization and surface tension measurements. The kinetics of gelation of these macromers showed correlation of polymerization rate with the length of the hydrophobic A block length. The increase in hydrophobic components may cause an increase in the micelle number concentration per unit volume, which is known to directly affect the rate of emulsion polymerization. The hydrophobic segment length is therefore a useful tool for controlling the gel formation on tissue.