Formation of methotrexate-PLLA-PEG-PLLA composite microspheres by microencapsulation through a process of suspension-enhanced dispersion by supercritical CO₂

Ai-Zheng Chen,^1,2 Guang-Ya Wang,¹ Shi-Bin Wang,^1,2 Li Li,¹ Yuan-Gang Liu,^1,2 Chen Zhao<sup>1

1</sup>College of Chemical Engineering, ²Institute of Pharmaceutical Engineering, Institute of Biomaterials and Tissue Engineering, Huaqiao University, Xiamen 361021, China

Background: The aim of this study was to improve the drug loading, encapsulation efficiency, and sustained-release properties of supercritical CO₂-based drug-loaded polymer carriers via a process of suspension-enhanced dispersion by supercritical CO₂ (SpEDS), which is an advanced version of solution-enhanced dispersion by supercritical CO₂ (SEDS).
Methods: Methotrexate nanoparticles were successfully microencapsulated into poly (L-lactide)-poly(ethylene glycol)-poly(L-lactide) (PLLA-PEG-PLLA) by SpEDS. Methotrexate nanoparticles were first prepared by SEDS, then suspended in PLLA-PEG-PLLA solution, and finally microencapsulated into PLLA-PEG-PLLA via SpEDS, where an "injector" was utilized in the suspension delivery system.
Results: After microencapsulation, the composite methotrexate (MTX)-PLLA-PEG-PLLA microspheres obtained had a mean particle size of 545 nm, drug loading of 13.7%, and an encapsulation efficiency of 39.2%. After an initial burst release, with around 65% of the total methotrexate being released in the first 3 hours, the MTX-PLLA-PEG-PLLA microspheres released methotrexate in a sustained manner, with 85% of the total methotrexate dose released within 23 hours and nearly 100% within 144 hours.
Conclusion: Compared with a parallel study of the coprecipitation process, microencapsulation using SpEDS offered greater potential to manufacture drug-loaded polymer microspheres for a drug delivery system.

Keywords: drug loading, encapsulation efficiency, methotrexate, nanoparticles, poly(L-lactide), supercritical CO₂ sustained release

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