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

Abstract

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.