Comparative study on the enzymatic degradation of poly(lactic-co-glycolic acid) by hydrolytic enzymes based on the colorimetric quantification of glycolic acid

Abstract

The enzyme-catalysed cleavage of ester bonds of poly(lactic-co-glycolic acid) (PLGA) has been monitored by an improved approach for the quantification of glycolic acid as indicator of copolymer hydrolysis. Glycolic acid released into the degradation medium was determined colorimetrically using chromotropic acid. The assay established is sensitive, as well as being both rapid and economical. The proposed method was applied to assess enzymatic degradation of a series of PLGA polyesters containing different proportions of monomers, end groups of PLGA chains and molecular weights. Among 22 commercially available hydrolytic enzymes (i.e. esterases, lipases and proteases) from different sources, the lipases from Candida antarctica, Candida cylindracea, Candida rugosa, Mucor miehei, Rhizopus arrhizus and porcine pancreas and the esterase from M. miehei all had a significant effect on PLGA degradation, often increasing the rate of ester bond cleavage by a factor of 25 compared to non-enzymatic hydrolysis. The most remarkable substrate specificity was observed for C. antarctica lipase with the rate of degradation being directly proportional to the glycolic acid content. In contrast, degradation by M. miehei esterase and R. arrhizus lipase were nearly independent of PLGA structure.