pH-Sensitive micelles with cross-linked cores formed from polyaspartamide derivatives for drug delivery.

A series of polyaspartamide derivatives were synthesized by grafting O-(2-aminoethyl)-O'-methylpoly(ethylene glycol) 5000 (MPEG), 1-(3-aminopropyl) imidazole (API), and cinnamate onto polysuccinimide (PSI) with the respective degrees of substitution adjusted by the feed molar ratio. The chemical structure of the prepared polymer was confirmed using FT-IR and (1)H NMR spectroscopy. A new pH-sensitive polymeric micelle based on the synthesized polymer was prepared and characterized, and its pH-sensitive properties were characterized by the measurement of light transmittance and particle sizes at varying pH values. pH-dependent aggregation and deaggregation behavior was clearly observed in the polymer aqueous dispersion system. Photo-cross-linking of the cinnamate branches cross-linked the core of the micelles. The core cross-linked micelles showed high stability over a wider pH range and displayed obvious pH-dependent swelling-shrinking behavior instead of micelle-unimer transition behavior. This micelle system overcame the drawback of the facile disintegration of normal polymeric micelles and showed obvious delayed paclitaxel release in in vitro drug delivery experiments.