Perfluorocarbon-Loaded Poly(lactide-<i>co</i>-glycolide) Nanoparticles from Core to Crust: Multifaceted Impactof Surfactant on Particle Ultrastructure, Stiffness, and Cell Uptake

Poly(lactide-<i>co</i>-glycolide) nanoparticles (PLGA NPs) loaded with Perfluoro-15-crown-5-ether (PFCE) have been developed for imaging applications. A slight modification of the formulation led to the formation of two distinct particle ultrastructures: multicore particles (MCPs) and core–shell particles (CSPs), where poly(vinyl alcohol) (PVA), a nonionic surfactant, and sodium cholate (NaCh), an anionic surfactant, were used, respectively. Despite their similar composition and colloidal characteristics, these particles have previously demonstrated significant differences in their <i>in vivo</i> distribution and clearance. We hypothesize that these differences are collectively driven by variations in their structural, chemical, and mechanical properties, which are investigated in this study. Nanomechanical characterizations of MCPs and CSPs by atomic force microscopy (AFM) revealed elastic modulus values of 54 and 270 MPa in water, respectively, indicating a better permeability and deformability of the multicore ultrastructure. The impact of the surfactant on the NP surface chemistry was evidenced by their protein corona, which was significantly greater in the CSPs. Additionally, an important amount of residual NaCh was found on the surface of CSPs, which formed strong interactions with bovine serum albumin (BSA), accounting for the difference in protein coronas and surface chemistry. Surprisingly, <i>in vitro</i> cell uptake studies showed a higher uptake of MCPs by RAW macrophages but a preference for CSPs by HeLa cells. We conclude that for this specific formulation and in this stiffness range, mechanical differences have a stronger impact in HeLa cells, while surface properties and chemical recognition play a more important role in uptake by macrophages. Overall, the extent to which a physical factor impacts cell uptake is highly dependent on the specific uptake mechanism. With this study, we provide an integrated perspective on the role of different surfactants in the particle formation process, their impact on particle ultrastructure, mechanical properties, and surface chemistry, and the overall effect on cell uptake <i>in vitro</i>.