Rational development of size-controlled polymeric nanoparticles : formulation optimization, particle characterization, and biological fates

Abstract

The introduction of nanotechnology to the pharmaceutical field has fostered a plethora of novel drug delivery systems with unique properties. Polymeric nanoparticles have in particular received considerable attention due to their additional merits of customizable materials and the feasibility of large-scale production. However, the attrition rate of drug-loaded polymeric nanoparticles remains substantial during the development stage. While this mitigated success is attributed to multiple factors, this thesis focused on the problems associated with the fabrication and characterization methods and the particle size effect.

The first part developed a novel analytical method combining the United States Pharmacopeia apparatus II (paddle) and centrifugal ultrafiltration for characterizing the in vitro drug release pattern of polymeric nanoparticles under sink conditions. Three different nanoparticles loaded with itraconazole, cholecalciferol (VitD3), and flurbiprofen were produced by flash nanoprecipitation (FNP) with D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) as the stabilizer for method validation and comparison. This new approach showed superior accuracy and repeatability compared with dialysis and other conventional methods. The data acquired by the new method was fitted to four typical mathematical models for drug release, concluding a predominant role of Fickian diffusion in the drug release from TPGS nanoparticles.

The second part employed the Design of Experiment (DoE) to examine the critical formulation and processing parameters of VitD3-loaded TPGS nanoparticles prepared by FNP. By manipulating the initial VitD3 concentration and the VitD3-TPGS ratio, six VitD3 nanoparticle formulations with different particle sizes between 40 and 150 nm were successfully developed, possessing essentially the same spherical shape and null zeta potential. They also exhibited satisfactory physical stability, nearly 100% encapsulation, and exceptionally high drug loadings. Their in vitro release profiles were determined by the aforementioned method in two media. All VitD3 nanoparticles showed undetectable VitD3 release in an aqueous medium containing 10% v/v fetal bovine serum, while a smaller particle size showed a higher release rate in 50% v/v ethanol. These different-sized VitD3 nanoparticles were further employed to investigate the particle size impact on their bio-fates. Mouse brain endothelial cells were used to establish an in vitro blood-brain barrier model. No cytotoxicity was observed in all formulations, while sub-60 nm VitD3 nanoparticles showed higher transcytosis efficiency. To accurately study the size effect on biodistribution, not only VitD3 but also its active metabolites (25-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3) were assayed in the biodistribution study. Results indicated that VitD3 nanoparticles with sizes < 110 nm would achieve higher plasma retention. VitD3 nanoparticles with sizes of 40 nm and 150 nm were superior for lung deposition, while particle size had no significant role in the brain uptake of VitD3 nanoparticles.

This study demonstrated the reliability of the newly developed analytical method for the in vitro release study, the feasibility of FNP to generate size-tunable nanoparticles with controlled particle properties through DoE, and the size effect on the bio-fate of polymeric nanoparticles. These results are anticipated to offer important insights into the size effect of polymeric nanoparticles ≤ 150 nm on their therapeutic potential and accelerate their clinical translation.