PH-responsive polymeric micelle based on PEG-poly(β-amino ester)/(amido amine) as intelligent vehicle for magnetic resonance imaging in detection of cerebral ischemic area

A series of pH-responsive polymeric micelles is developed to act as intelligent carriers to deliver iron oxide (Fe ₃O ₄) nanoparticles and respond rapidly to an acidic stimuli environment for magnetic resonance imaging (MRI). The polymeric micelle can be self-assembled at physiological pH by a block copolymer, consisting of a hydrophilic methoxy poly(ethylene glycol) (PEG) and a pH-responsive poly(β-amino ester)/(amido amine) block. Consequently, the Fe ₃O ₄ nanoparticles can be well encapsulated into polymeric micelles due to the hydrophobic interaction, shielded by a PEG coronal shell. In an acidic environment, however, the pH-responsive component, which has ionizable tert-amino groups on its backbone, can become protonated to be soluble and release the hydrophobic Fe ₃O ₄ nanoparticles. The Fe ₃O ₄-loaded polymeric micelle was measured by dynamic light scattering (DLS), superconducting quantum interference device (SQUID) and a 3.0 T MRI scanner. To assess the ability of this MRI probe as a pH-triggered agent, we utilize a disease rat model of cerebral ischemia that produces acidic tissue due to its pathologic condition. We found gradual accumulation of Fe ₃O ₄ nanoparticles in the brain ischemic area, indicating that the pH-triggered MRI probe may be effective for targeting the acidic environment and diagnostic imaging of pathologic tissue.