Something new in the field of PLA/GA bioresorbable polymers?

Polymers issued from glycolic acid and lactic acids (PLAGA) are now used worldwide as bioresorbable devices in surgery and in pharmacology. Their abiotic hydrolytic degradation has been shown to depend on diffusion-reaction phenomena and to proceed homogeneously or heterogeneously, depending on many factors. Two initiators are presently used industrially to make PLAGA polymers by ring opening polymerisation of lactide and/or glycolide in the bulk, namely Sn octanoate and zinc metal. In this contribution, attention is paid to the differences generated by the use of these two initiator systems in the case of the polymerisation of DL-lactide. Various poly(DL-lactide)s were prepared and characterised by size-exclusion chromatography (SEC), differential scanning calorimetry (DSC) and nuclear magnetic resonance spectroscopy (NMR). These polymers were allowed to age in pH=7.4 isoosmolar phosphate buffer at 37 degrees C. Under these conditions, polymers prepared by the two initiator systems showed dramatic differences when the fates of parallel sided specimens of rather large dimensions were considered. These differences were related to the esterification of some of the OH chain ends by octanoic acid and to the presence of rather hydrophobic low molecular weight by-products which were insoluble in the solvent generally used to purify the crude PLAGA polymers. These new findings should be of great interest in the case of PLAGA based matrices aimed at drug delivery.