Amphiphilic Toothbrushlike Copolymers Based on Poly(ethylene glycol) and Poly(ε-caprolactone) as Drug Carriers with Enhanced Properties

Amphiphilic poly(ethylene glycol)-b-poly(2-hydroxyethyl methacrylate-g-poly(epsilon-caprolactone)) (PEG-b-P(HEMA-g-PCL)) toothbrushlike copolymers were synthesized and evaluated as drug delivery carriers. Two toothbrushlike polymers were synthesized via ring-opening polymerization of epsilon-caprolactone (CL) initiated by poly(ethylene glycol)-b-poly(2-hydroxyethyl methacrylate) (PEG-b-PHEMA) macromolecular initiators, and their molecular structures and physical properties were characterized using H-1 NMR, gel permeation chromatography (GPC), and differential scanning calorimetric analysis (DSC). The melting points and crystallizable temperature have been decreased obviously, implying that the PCL cores of PEG-b-P(HEMA-g-PCL) toothbrushlike copolymer micelles with shorter PCL segments were unlikely to crystallize at room temperature for drug delivery application. Also the micellization properties of toothbrushlike copolymers in aqueous solution were investigated by fluorescence spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM). Compared with the micelles from linear PEG-b-PCL block copolymers, the micelles of PEG-b-P(HEMA-g-PCL)s exhibited higher loading capacity to the anticancer drug, doxorubicin (DOX), and the drug-loaded micelles were highly stable in aqueous solution. In vitro DOX release data and confocal laser scanning microscopy (CLSM) studies showed that DOX-loaded toothbrushlike copolymer micelles could be effectively internalized by bladder carcinoma El cells, and the DOX could be released into endocytic compartments and finally transported to the nucleus. Such toothbrushlike copolymer micelles can be analogues of linear PEG-b-PCL diblock copolymers, but demonstrated better properties of loading and release due to their hydrophobic PCL cores do not crystallize at delivery conditions.