Polymer Vesicles with a Red Cell-like Surface Charge: Microvascular Imaging and in vivo Tracking with Near-Infrared Fluorescence.

Polymersomes are block copolymer-based vesicles whose long circulation times or "stealth" in vivo coupled with the loading and controlled release of drugs, siRNA, and other compounds has made them attractive for delivery. A brushy corona of non-ionic polyethylene glycol (PEG) likely contributes stealth, but red blood cells (RBCs) possess a negatively charged glycocalyx and circulate much longer. Polyanionic block copolymers were therefore mixed into polymersomes which were also labeled with a near IR fluorophore to quantify biodistribution in live mice and excised organs. Charge shifts tissue distribution, and high resolution imaging of vesicles in blood capillaries further shows that organ cultures can provide deeper insight into microscale transport within tissue microenvironments.