(123d) Continuous Synthesis of Drug-Loaded PLGA Nanoparticles Enabled By Ultrasonic Microreactor

Poly (D, L lactic-co-glycolic acid) (PLGA) nanoparticles have shown immense potential as carriers for drugs, proteins, and other macromolecules for their controlled release¹. PLGA nanoparticles with a diameter in the range of 20-200 nm are best suited for drug delivery². Nanoprecipitation has been implemented utilizing microreactors for the synthesis of PLGA nanoparticles (diameter 40-200 nm), however, a major drawback is a low throughput (typically below 10 mg/hr.) and class 2 toxic solvents like acetonitrile and dimethylformamide ^3–5. European Medicines Agency recommends avoiding or limiting the use of class 2 solvents due to their significant toxicities⁵. An alternative is the emulsion-solvent evaporation technique coupled with batch ultrasonic emulsification for the synthesis of PLGA nanoparticles. Emulsion-solvent evaporation utilizes ethyl acetate as a solvent, which is classified as a class 3 (low toxic potential and recommended)⁵. However, batch synthesis suffers from drawbacks such as batch-to-batch variation, lack of particle size control, the possibility of contamination, and mean hydrodynamic diameter (MHD) larger than 120 nm ^6,7. In this work, we will present an ultrasonic microreactor for the synthesis of drug-loaded PLGA nanoparticles in the desired size range (20-200 nm) utilizing emulsion-solvent evaporation technique.

The ultrasonic microreactor, consisting of a borosilicate glass reactor with a serpentine channel of square cross-section 1.2x1.2 mm² and a length of 700 mm (volume ~ 1 ml) bonded to a piezoelectric plate transducer of thickness 4 mm, is operated at the frequency of 550 kHz. For the generation of the PLGA nanoparticles, the continuous phase (Milli-Q water + Poloxamer 407) and the dispersed phase (PLGA (+ drug cyclosporin A) + ethyl acetate) are supplied to the reactor for the flow rate of 200 μl/min and 50 μl/min respectively (residence time 4 min). The particle size of the PLGA nanoparticles is analyzed by dynamic light scattering (DLS).

Blank PLGA nanoparticles of MHD 85 nm and polydispersity index (PDI) 0.14 are synthesized by batch solvent evaporation, for the power of 15 W. Next, the ultrasonic microreactor is coupled with a 3D-printed open channel (200x10x5 mm³) for the continuous solvent evaporation to enable the continuous synthesis of the PLGA nanoparticles (Figure 1 (a) and (b)). The outlet of the open channel is connected to a sample collection syringe mounted on a syringe pump to maintain a steady flow. Three independent experiments for the continuous synthesis of blank PLGA nanoparticles at the power of 15 W show the results are reproducible (Figure 1(c)). In addition, no significant influence of the ultrasonic power is seen on the PLGA nanoparticle size (Figure 1(d)).

In this study, we will present an ultrasonic microreactor coupled with a 3D-printed channel for the continuous synthesis of drug-loaded PLGA nanoparticles for the desired size range of 20-200 nm. We will encapsulate the immunosuppressant drug Cyclosporin A in the PLGA nanoparticles and quantify the encapsulation efficiency and drug loading. Finally, we will study the in-vitro release of the drug from the PLGA nanoparticles. The current study will demonstrate the synthesis of monodisperse drug-loaded PLGA nanoparticles (MHD < 100 nm, PDI < 0.3) for drug delivery utilizing a non-toxic solvent.

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