Stable polymersomes based on ionic–zwitterionic block copolymers modified with superparamagnetic iron oxide nanoparticles for biomedical applications

Abstract

Stable polymersomes with semipermeable membranes were prepared by simple mixing of two oppositely charged diblock copolymers containing zwitterionic and cationic (PMPC₂₀-b-PMAPTAC₁₉₀) or anionic (PMPC₂₀-b-PAMPS₁₉₆) blocks. The formation of vesicular structures in the mixed solution of the block copolymers was confirmed by direct observation using the cryo-TEM technique. Superparamagnetic iron oxide nanoparticles coated with a cationic chitosan derivative (SPION/CCh) and decorated with a fluorescent probe molecule were next incorporated into the polymersome structure. The average diameter of SPION/CCh-polymersomes estimated using cryo-TEM was about 250 nm. Surface topography of the SPION/CCh-loaded vesicles was imaged using AFM and the magnetic properties of these objects were confirmed by MFM and MRI measurements. The ability of SPION/CCh-polymersomes to affect T₂ relaxation time in MRI was evaluated based on the measurements of r₂ relaxivity. The obtained value of r₂ (573 ± 10 mM⁻¹ s⁻¹) was quite high. The cytotoxicity and intracellular uptake of the SPION/CCh-loaded vesicles into EA.hy926 cells were studied. The results indicate that the SPION/CCh-polymersomes seem to be internalized by vascular endothelium and are not cytotoxic to endothelial cells up to 1 μg Fe per mL. Therefore, it can be suggested that SPION/CCh-polymersomes could prove useful as T₂ contrast agents in the MRI of endothelium.