Shape-Dependent Cellular Uptake of Nanostructures Produced from Supramolecular Structure-Directing Unit-Appended Hydrophilic Polymers

Cellular uptake is an important event in drug delivery and other biomedical applications. Amphiphilic polymers produce aggregates of different size and shape depending on the intrinsic structural differences and the packing parameter. Although they have been explored for various biomedical applications with immense interest, the relationship between the shape of the aggregate and cellular uptake has been studied only in limited examples. This work reports two polymers (P1 and P2), both of which contain a hydrophobic supramolecular structure-directing unit (SSDU) at the chain-end of a fluorescence dye-labeled hydrophilic polymer. Depending on the difference in the structure of the single H-bonding functional group (hydrazide or amide) of the SSDU, P1 and P2 produce polymersomes (NS1) and spherical micelles (NS2), respectively. An aged solution of P2 produces cylindrical micelles (NS3). Confocal microscopy studies reveal that the uptake of these nanostructures in HeLa cells greatly depends on the shape of the aggregate. Spherical NS1 and NS2 show appreciable uptake at 1 or 4 h of incubation, whereas NS3 shows negligible uptake. Temperature-dependent cellular uptake studies reveal an energy-dependent endocytosis pathway. Kinetic studies show gradual increase in the cellular uptake with time, and at 24 h the relative uptake ratio (NS1:NS2:NS3) is 1.0:0.2:<0.1, implying the polymersome morphology (NS1) is most efficient for cellular uptake compared to the spherical or cylindrical micelles. The same trend was also noticed for MDA-MB 231 cells. Confocal microscopy studies further reveal cellular internalization and intracellular location of NS1, which showed maximum cellular uptake. As the intrinsic difference in the chemical structure of the two polymers is negligible, the observed difference can be explicitly assigned to their difference in shape.