Resorcinarene-centered amphiphilic star-block copolymers: Synthesis, micellization and controlled drug release

Eight-arm star-shaped poly(ɛ-caprolactone)-block-poly(ethylene glycol)s (SPCL-b-PEG) have been prepared by a combination of controlled ring-opening polymerization (CROP) and coupling reaction. First, eight-arm star-shaped poly(ɛ-caprolactone)s (SPCL) with a resorcinarene core were synthesized using octamethyl tetraundecylresorcinarene octaacetate as octa-initiator and yttrium tris(2,6-di-tert-butyl-4-methylphenolate) [Y(DBMP)3] as catalyst. Then the coupling reaction was carried out between SPCLs and carboxyl-terminated methoxy poly(ethylene glycol)s (mPEG-COOH) in the presence of N,N′-dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP), resulting in eight-arm star-shaped SPCL-b-PEGs with controlled molecular weight and well-defined architecture. Furthermore, these amphiphilic eight-arm SPCL-b-PEGs could self-assemble into micelles with low critical micellar concentrations (CMC), which was characterized by fluorescent spectroscopy. Moreover, indomethacin loaded micelles with high drug loading content and high encapsulation efficiency can be prepared, which is probably due to the highly branched architecture. The morphologies of micelles were characterized by transmission electron microscopy (TEM), which exhibited diverse nanostructures as the drug loading contents varied. In vitro drug release of indomethacin from SPCL-b-PEG micelles was carried out in PBS, from which a sustained release behavior was observed. SPCL-b-PEG micelles did not show significant cytotoxicity at copolymer concentrations up to 1000 mg/L, making them very promising for drug delivery.