Role of phase diagram of membrane formation system in controlling the crystallinity and degradation rate of PLLA membranes

In this work, the theoretical phase diagram of membrane formation system of ethanol, methylene chloride, and poly-L-lactide (PLLA) was studied. On the basis of the phase diagram, particulate and porous membranes, dominated by crystallization and liquid-liquid demixing, respectively, were prepared. Furthermore, degradation of PLLA membranes with particulate, porous, and dense morphologies was performed in phosphate buffered solution (PBS) at 37°C for 168 days and was investigated by mass loss, scanning electron microscopy (SEM), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). Besides the membrane morphology, a close relationship between the phase behavior of the membrane formation system and the membrane crystallinity was found, which in turn influenced the degradation rate of these membranes significantly. In the case of dense membranes, it showed the lowest initial crystallinity and the greatest rate of mass loss and molecular weight decrease compared with particulate and porous membranes. In contrast, the particulate membranes had the highest crystallinity and the slowest degradation rate in this study. Therefore, the phase diagram of membrane formation system could not only anticipate membrane morphology, but could also control the membrane crystallinity and degradation rate simultaneously.