The influence of manufacturing procedure on the degradation of poly(lactide-co-glycolide) 85:15 and 50:50 implants

Poly(lactides-co-glycolides) (PLGA) are widely investigated biodegradable polymers and are extensively used in several biomaterials applications as well as drug delivery systems. The PLGA polymers degrade by bulk hydrolysis of ester bonds and breakdown into their constituent monomers, lactic and glycolic acids which are excreted from the body. The purpose of this investigation was to study the effect of manufacturing procedure on the in vitro degradation of two PLGA copolymers, 85:15 and 50:50, which were fabricated as implants, Implants were compressed from microcapsules prepared by nonsolvent induced phase separation using two solvent-nonsolvent systems, viz., methylene chloride-hexane (non-polar) and acetone-phosphate buffer (polar). Studies were performed at pH 4.5, 7.4 and 9.4 and polymer degradation was monitored by measuring the decrease in number- and weight-average molecular weights (M(n) and M(w)), mass loss, formation of lactic and glycolic acids and pH of the degradation medium. Representative scanning electron micrographs (SEMs) were also obtained to study the changes in surface morphology of the implants. Results of these studies indicated that both PLGA 85:15 and 50:50 implants prepared by the non-polar procedure degraded faster than the implants prepared by the polar procedure. The decrease in polymer M(n) and M(w) followed pseudo first-order kinetics. Changes in M(n) and M(w) occurred before the onset of mass loss, after which implant mass loss was described by pseudo first order kinetics. The appearance of lactic and glycolic acids corresponded to the initiation of mass loss and also resulted in decrease in pH of the bulk degradation medium. The SEMs indicated that water uptake was faster in implants prepared by the non-polar method resulting in a more porous matrix which degrades more rapidly. Finally, the average degradation time for PLGA 85:15 was approximate to 26 weeks and that for PLGA 50:50 was 6-8 weeks.