Synthesis\nand Characterization of Gold-Nanoparticle-Loaded\nBlock Copolymer Vectors for Biomedical Applications: A Multivariate\nAnalysis

Gold\nnanoparticles (GNPs) encapsulated in amphiphilic block copolymers\nare a promising system for numerous biomedical applications, although\ncritical information on the effects of various preparation variables\non the structure and properties of this unique type of nanomaterial\nis currently missing from the literature. In this research, we synthesized\nGNPs functionalized with thiol-terminated polycaprolactone (PCL-GNPs)\nbefore encapsulating them into poly(ε-caprolactone)-<i>b</i>-poly(ethylene glycol) (PCL-<i>b</i>-PEG) micellar\nnanoparticles via nanoprecipitation to yield GNP-loaded polymeric\nnanoparticles (GNP-PNPs). We explored the role of different manufacturing\nvariables (water volume, PCL-<i>b</i>-PEG to PCL-GNP ratio,\nand PEG block length) on the sizes, morphologies, GNP occupancies,\ncolloidal gold concentrations, and time stability of GNP-PNPs. Despite\nour motivation to increase colloidal gold concentrations for K-edge\nCT imaging applications, there was only moderate variation in the\nconcentration of colloidal gold (<i>c</i><sub>Au</sub> =\n∼100–150 μg/mL) over the range of investigated\nexperimental variables; however, postformulation exposure to compressed\nair flow provided samples with increased gold concentrations and CT\ncontrast above the visual threshold in imaging phantoms. The range\nof formulation variables also had only a weak effect on mean effective\nhydrodynamic diameters (<i>d</i><sub>h,eff</sub> = ∼150\nnm). Statistical analysis of TEM images revealed that the mean number\nof GNPs within GNP-PNP vectors smaller than 50 nm, <i>Z</i><sub>ave,<i>d</i><50 nm</sub>, is generally higher\nfor preparations involving PCL-<i>b</i>-PEG with the shorter\nof the two different PEG block lengths. Preparations with the shorter\nPEG block length copolymer were also found to produce GNP-PNP colloids\nwith greater time stability in <i>d</i><sub>h,eff</sub> and <i>c</i><sub>Au</sub>. Consistent with our previous study using\nMB-MDA-231 cells, we found increased gold uptake in MCF-7 cells with\nincreasing <i>Z</i><sub>ave,<i>d</i><50 nm</sub>. This study provides a roadmap for optimizing important figures\nof merit for existing biomedical applications, including CT imaging\nand radiotherapy sensitization, and for developing new diagnostic\nand therapeutic strategies using GNP-PNPs.