Mammalian cells preferentially internalize hydrogel nanodiscs over nanorods and use shape-specific uptake mechanisms

Abstract

Size, surface charge, and material compositions are known to influence cell uptake of nanoparticles. However, the effect of particle geometry, i.e., the interplay between nanoscale shape and size, is less understood. Here we show that when shape is decoupled from volume, charge, and material composition, under typical in vitro conditions, mammalian epithelial and immune cells preferentially internalize disc-shaped, negatively charged hydrophilic nanoparticles of high aspect ratios compared with nanorods and lower aspect-ratio nanodiscs. Endothelial cells also prefer nanodiscs, however those of intermediate aspect ratio. Interestingly, unlike nanospheres, larger-sized hydrogel nanodiscs and nanorods are internalized more efficiently than their smallest counterparts. Kinetics, efficiency, and mechanisms of uptake are all shape-dependent and cell type-specific. Although macropinocytosis is used by both epithelial and endothelial cells, epithelial cells uniquely internalize these nanoparticles using the caveolae-mediated pathway. Human umbilical vein endothelial cells, on the other hand, use clathrin-mediated uptake for all shapes and show significantly higher uptake efficiency compared with epithelial cells. Using results from both upright and inverted cultures, we propose that nanoparticle internalization is a complex manifestation of three shape-and size-dependent parameters: particle surface-to-cell membrane contact area, i.e., particle-cell adhesion, strain energy for membrane deformation, and sedimentation or local particle concentration at the cell membrane. These studies provide a fundamental understanding on how nanoparticle uptake in different mammalian cells is influenced by the nanoscale geometry and is critical for designing improved nanocarriers and predicting nanomaterial toxicity.cell-uptake mechanism | nanoimprint lithography | drug delivery P olymeric nanoparticles are widely studied for delivering therapeutic and imaging payloads to cells. Understanding how particle properties affect cell uptake is not only critical for designing improved therapeutic and diagnostic agents (1, 2) but also essential for efficient in vitro cell manipulation (3) and evaluating nanomaterial toxicity (4). Nanoparticle uptake by cells has been shown to depend on particle size, surface charge, and material compositions (5-7). Recent advances in fabrication technologies have enabled generation of shape-specific microparticles and nanoparticles (8-12). These particles, inspired by the diverse, evolutionarily conserved shapes of pathogens and cells, are being used to study the role of carrier shape on cellular internalization, in vivo transport, and organ distribution (6,11,(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23).Despite these pioneering studies, there remains a significant knowledge gap in our fundamental understanding of the interplay between nanoscale shape and size on cellular internalization, especially for clinically relevant polymer-based hydrophilic nanoparticles. Most in vivo drug delivery and imaging applicati...

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