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-coglycolide) (PLGA) films as a function of exposure time to an aque ous medium and to correlate the mechanical properties to the degradation/er osion of the polymer as a function of the type of polymer [PLA, weight-aver age 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)], an d the exposure time to pH 7.4 phosphate buffer. The glass transition temper ature of the films was measured by differential scanning calorimetry (DSC), the molecular weight by size exclusion chromatography (SEC), and the polym er erosion and hydration gravimetrically. The mechanical properties were st rongly affected by the type of polymer and plasticizer. PLGA films showed a faster loss of mechanical integrity. TEC, the water-soluble plasticizer, l eached from the films, resulting in major differences in the mechanical pro perties (flexibility) when compared with films plasticized with the more pe rmanent, water-insoluble ATBC. A significant difference in M-W decrease was seen between plasticizer-free and plasticizer-containing PLA films, but no t for PLGA films. Plasticized PLA films, which were above their glass trans ition temperature in the rubbery state, showed a faster decrease in M-W tha n plasticizer-free PLA ones, which were in the glassy state. The plasticize r addition to the lower M-W PLGA did not enhance the polymer degradation; t he plasticizer-free PLGA was already in the rubbery state. Major difference s between the two polymers were also seen in the mass loss and the water up take 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. and the American Pharmaceutical Associa tion J Pharm Sci 89:1558-1566; 2000.