Structure formation in injectable poly(lactide-co-glycolide) depots.

Solutions of low-molecular-weight poly(lactide-co-glycolide) (PLGA) in organic solvents have been investigated as novel injectable drug depots for drug delivery over periods of weeks to months. In this paper, we investigated the structure formation in a PLGA/benzyl benzoate system, using controlled stress rheometry, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). GPC analysis demonstrated a decrease in molecular weight as a function of time and temperature, indicating degradation. Rheological experiments showed that the flow properties of PLGA/benzyl benzoate solutions were affected by a combination of degradation and gelation; the latter was also detected by an endotherm in DSC and by three-dimensional structure formation studies by rheology. Extent of degradation and gelation of PLGA were shown to depend on the solvent.