Generation of porous poly-l-lactide microspheres by emulsion-combined precipitation with a compressed CO2 antisolvent process

Abstract

An emulsion-combined precipitation of compressed CO₂ antisolvent (PCA) process was used to fabricate porous poly-L-lactide (PLLA) microspheres (PLLA PMs). A 2⁴ full factorial experiment was performed to optimize the operating process and analyze the effect of the factors on the size and morphology of the PLLA PMs. An investigation of their in vitro cytotoxicity was also performed. Taking methotrexate (MTX) as a drug model, MTX-loaded PLLA PMs (MTX-PLLA PMs) were fabricated by the optimized process. Drug loading behaviors and in vitro inhibitory activity against A549 lung cancer cells were also evaluated. The resulting PLLA PMs and MTX-PLLA PMs both exhibited a porous and uneven morphology, with a density less than 0.4 g cm⁻³, a geometric mean diameter (D_g) of 10–25 μm, an aerodynamic diameter (D_a) less than 4.7 μm, a fine particle fraction (FPF) of 58–62%, and a porosity of 79–85%, meeting the requirements for pulmonary drug delivery. Various characterizations revealed that no chemical change occurred in the PLLA, while a slight shift in the molecular structure of MTX was observed after the process, as well as a change in its physical state from crystalline to amorphous. No obvious cytotoxicity was detected for the PLLA PMs, and the MTX-PLLA PMs displayed a sustained release profile with an encapsulation efficiency (EE) of 81.6%. The fluorescent MTX-PLLA PMs also revealed that most of the drug was homogeneously distributed inside the matrix. An in vitro antitumor assay indicated that the MTX-PLLA PMs possessed a sustained and improved inhibitory activity compared with the raw MTX. This study demonstrates that the emulsion-combined PCA process has potential for developing a promising inhalable carrier for pulmonary drug delivery.