PLA-PEG copolymers micronization by Supercritical Assisted Atomization

Supercritical assisted atomization (SAA) under reduced pressure was used to produce microparticles with defined spherical morphology, controlled particle size and distribution of PEG–PLA copolymers. These compounds, because of their low glass transition temperature are difficult to process using other techniques. Different architectures were tested to optimize PEG–PLA copolymers from the point of view of SAA processability and their pharmaceutical application. Synthesis and micronization of copolymers with relative content of PEG:PLA of 1:4 (w/w) and 1:8 (w/w) and with atactic or stereoregular (isotactic) PLA arms were performed and the architectures of linear copolymers (, PEG(PLA)), branched of first generation (G1, PEG(PLA)2) and branched of second generation (G2, PEG(PLA)4), characterized by one, two and four PLA arms respectively, were tested. Well defined particles of the linear copolymer PEG–PLA, with isotactic PLA chain, were obtained with a mean particle size of 0.25–0.45 μm, for both PEG:PLA ratios. G2 branched copolymer were successfully micronized in the case of 1:8 PEG:PLA ratio with isotactic PLA blocks and spherical particles with a mean particle size of about 0.3 μm were obtained. On the contrary, the G1 copolymers with isotactic PLA arms formed coalescing microparticles when processed by SAA. Copolymers with atactic PLA arms, independently on the architecture, were not successfully processable. SAA process did not modify the structure of the starting copolymers, as shown by 1H NMR and GPC analyses. The microparticles obtained showed a lower degree of crystallinity compared to the untreated materials, as confirmed by XRPD and DSC analyses. The G2 branched 1:8 PEG:PLA copolymer, because of the structure and the size of the obtained particles, can be considered the most promising for the controlled release of a drug.