ATV solubilization As reported recently, poly(2-oxazoline) (POx) and poly(2-oxazine) (POzi) based ABA triblock copolymers, all comprising the same hydrophilic poly(2-methyl-2-oxazoline) (PMeOx) shell A and structurally very similar, hydrophobic cores B exhibit different loading capacities for various hydrophobic drugs [50, 53-57] as well as varying drug/polymer interactions in dependence of the drug-loading [58, 59] . Whereas the triblock copolymer with a barely hydrophobic poly(2-n-butyl-2-oxazoline) (pBuOx, = A-pBuOx-A) core enabled moderately high loadings of 24 wt.% of the hydrophobic compound curcumin (CUR), its structural isomer with a poly(2-n-propyl-2-oxazine) (pPrOzi; = A-pPrOzi-A) core was able to yield exceptionally high loadings up to 54 wt.%. Interestingly, in the case of hydrophobic paclitaxel (PTX), the situation was vice versa, A-pBuOx-A being the best performer with PTX loadings up to 48 wt.% compared to 25 wt.% in the case of A-pPrOzi-A. As the drug loading is a crucial parameter concerning the translation of drugloaded polymer micelles into the clinics, we investigated both polymers with regard to their solubilization capacity for the non-water soluble drug atorvastatin (ATV; water solubility of ATV calcium salt trihydrate by thin film-method = 60 mg/L (0.1 mM); analyzed in house). Additionally, two polymers comprising either a poly(2n-propyl-2-oxazoline) (pPrOx; = A-pPrOx-A) or poly(2-n-butyl-2oxazine) (pBuOzi; = A-pBuOzi-A) core were investigated for solubilization. The mixture of two Pluronics® SP1049C, which was developed by Kabanov for the interference with P-glycoprotein (Pgp) and therefore, improved delivery of hydrophobic molecules across biological barriers such as the BBB overexpressing P-gp was included for comparison (Figure ). As expected, distinct polymer-ATV solubilization specificities were observed for the formulations prepared by thin film method (Figure ). Whereas A-pPrOx-A enabled ATV concentrations of only 0. Particle sizes of the A-pBuOzi-A/ATV formulations were highly dependent on the ATV-loading. At rather low loadings of 0.5 and 0.9 g/L (polymer = 10 g/L), micelles with average hydrodynamic diameters D h of 15 nm and 26 nm were found, respectively (Figure ). The size distributions were monomodal with corresponding PDIs of 0.22 (Figure ). Increasing the ATV-loading to 2.8 and 4.0 g/L resulted in a dramatic increase in particle size to 609 nm and 847 nm, respectively, accompanied by an increase in PDI to 0.31 -0.32. The increase in size was also apparent by visual inspection of the formulations (inset Figure ). Whereas up to A-pBuOzi-A/ATV = 10/0.8 g/L the formulations were completely clear, the sample containing 2.8 g/L ATV was opaque and emulsion-like (however samples for DLS were diluted 1/5 (v/v) to suppress artefacts due to multiple scattering etc.). Although being opaque, the samples did not show precipitation over extended periods of time (determined by visual inspection as well as relatively constant ATV loading up to 30 d (ATV feed = 5 & 8 g/L) or 10 d (ATV feed = 10 g/L) storage (Figure )). A more detailed analysis of these aggregates using, inter alia, small angle neutron scattering is ongoing. However, such large aggregates, irrespective of their nature or structure are probably not ideal for the envisioned application i.v. for which smaller and better-defined micelles are preferred.