Physicomechanical properties of biodegradable poly(D,L-lactide) and poly(D,L-lactide-co-glycolide) films in the dry and wet states.

The objective of this study was to investigate the mechanical properties (% elongation and puncture strength) of poly(D,L-lactide) (PLA) and poly(D,L-lactide-co-glycolide) (PLGA) films as a function of exposure time to an aqueous medium and to correlate the mechanical properties to the degradation/erosion of the polymer as a function of the type of polymer [PLA, weight-average molecular weight (M(W)) 270,300, or PLGA 50:50, M(W) 56,500], the type of plasticizer [(triethyl citrate (TEC) or acetyltributyl citrate (ATBC)], and the exposure time to pH 7.4 phosphate buffer. The glass transition temperature of the films was measured by differential scanning calorimetry (DSC), the molecular weight by size exclusion chromatography (SEC), and the polymer erosion and hydration gravimetrically. The mechanical properties were strongly affected by the type of polymer and plasticizer. PLGA films showed a faster loss of mechanical integrity. TEC, the water-soluble plasticizer, leached from the films, resulting in major differences in the mechanical properties (flexibility) when compared with films plasticized with the more permanent, water-insoluble ATBC. A significant difference in M(W) decrease was seen between plasticizer-free and plasticizer-containing PLA films, but not for PLGA films. Plasticized PLA films, which were above their glass transition temperature in the rubbery state, showed a faster decrease in M(W) than plasticizer-free PLA ones, which were in the glassy state. The plasticizer addition to the lower M(W) PLGA did not enhance the polymer degradation; the plasticizer-free PLGA was already in the rubbery state. Major differences between the two polymers were also seen in the mass loss and the water uptake studies. After 4 weeks, the mass loss was between 2.6 and 7.0% and the water uptake between 10.1 and 21.1% for PLA films, whereas for PLGA films, the mass loss was between 40.3 and 51.3% and the water uptake between 221.9 and 350.6%. 2000 Wiley-Liss, Inc.