Enhancement of cellular uptake by increasing the number of encapsulated gold nanoparticles in polymeric micelles

We apply a combination of polycaprolactone (PCL)-thiol ligand functionalization with flow-controlled microfluidic block copolymer self-assembly to produce biocompatible gold nanoparticle (GNP)-loaded micellar polymer nanoparticles (GNP-PNPs) in which GNPs are encapsulated within PCL cores surrounded by an external layer of poly(ethylene glycol) (PEG). By varying both the relative amount of block copolymer and the microfluidic flow rate, a series of GNP-PNPs are produced in which the mean number of GNPs per PNP in the < 50-nm fraction (Z(ave,d) (< 50 nm)) varies between 0.1 and 1.9 while the external PEG surface is constant. Z(ave,d) (< 50 nm) values are determined by statistical analysis of TEM images and compared with the results of cell uptake experiments on MDA-MB-231 cancer cells. For Z(ave,d) (< 50 nm) <= 1 (including a control sample of individual GNPs also with a PEG surface layer), cell uptake is relatively constant, but increases sharply for Z(ave,d) (< 50 nm) > 1, with a factor of 7 enhancement as Z(ave,d) (< 50 nm) increases from 1 to similar to 2. Enabled by the shear processing control provided by the microfluidic chip, these results provide the first evidence that cellular uptake can be enhanced specifically by increasing the number of GNPs per vector, with other parameters, including polymeric material, internal structure, and external surface chemistry, held constant. They also demonstrate a versatile platform for packaging GNPs in biocompatible polymeric carriers with flow-controlled formulation optimization for various therapeutic and diagnostic applications.