Effect of zwitterionic sulfobetaine incorporation on blood behaviours, phagocytosis, and in vivo biodistribution of pH-responsive micelles with positive charges

pH-responsive micelles with positive charges are challenged by their significant effect on the cells/proteins and compromise their final fate due to electrostatic interactions. As one of the promising strategies, zwitterion incorporation in micelles has attracted considerable attention and displayed improved protein adsorption and blood circulation performances. However, previous reports in this field have been mostly limited in hemolysis for studying blood behaviour and lack a comprehensive understanding of their interactions with blood components. Herein, we present a prelimilary study on the effect of zwitterionic sulfobetaine incorporation on blood behaviour, phagocytosis, and in vivo biodistribution of pH-responsive micelles with positive charges. Amphiphilic triblock copolymers, namely poly(epsilon-caprolactone)-b-poly(N,N-diethylaminoethyl methacrylate)-(N-(3-sulfopropyl-N-methacryloxyethy-N,N-diethylammonium betaine)) (PCL-PDEAPS(x), x = 2, 6, 10), containing different numbers of sulfobetaine groups were synthesized through four steps to prepare the pH-responsive micelles with positive charges. The effect of the sulfobetaine incorporation displayed different profiles, e.g., the micelles had no effect on RBC aggregation, thrombin time (TT), and platelet aggregation, while the cytotoxicity, hemolysis, RBC deformability, activated partial thromboplastin time (APTT), prothrombin time (PT), platelet activation, protein (albumin, fibrinogen, plasma) adsorption, phagocytosis, and in vivo biodistribution decreased with the increase in the sulfobetaine number, in which the transition mainly occurred at a sulfobetaine/tertiary amine group ratio of 3/7-1/1 compared to that of the mPEG control. In addition, the micelles displayed a strong inhibitory effect on the intrinsic coagulation pathway, which was associated with a significant decrease in the coagulation factor activity. Based on these findings, the related mechanism is discussed and proposed, which can aid the rational design of pH-responsive micelles for improved therapeutics.