Development of a pH-sensitive polymer using poly(aspartic acid-graft-imidazole)-block-poly(ethylene glycol) for acidic pH targeting systems

Abstract

pH sensitive polymer systems can be utilized as smart nanocarriers to deliver hydrophobic drugs specifically to solid tumors or to acidosis-affected rheumatic joints. In this study, a poly(L-aspartic acid-graftimidazole)-block-poly(ethylene glycol) (P(Asp-g-Im)-PEG) block copolymer was synthesized as a pH sensitive nanocarrier targeting acidic pH environments. The polypeptide P(Asp), which was used as a backbone for the hydrophobic block, was synthesized by ring opening polymerization with N-carboxylanhydride (NCA) of beta-benzyl-aspartic acid. PEG was included as the hydrophilic block and the polymer was functionalized with imidazole groups to confer pH sensitivity. The prepared P(Asp-g-Im)-PEG is zwitterionic with a pI 6.5; 60% of the available carboxyl groups of P(Asp)-PEG were substituted by imidazole groups. Furthermore, the potentiometric titration curve of P(Asp-g-Im)-PEG demonstrated a broad buffer zone. The micelles prepared from P(Asp-g-Im)-PEG showed pH dependent critical micelle concentrations (CMC), particle sizes, zeta potentials, and morphologies.