A new synthesis method and degradation of hyper-branched polyethylenimine grafted polycaprolactone block mono-methoxyl poly (ethylene glycol) copolymers (hy-PEI-g-PCL-b-mPEG) as potential DNA delivery vectors

Hyper-branched polyethylenimine grafted polycaprolactone block mono-methoxyl poly (ethylene glycol) copolymer (hy-PEI-g-PCL-b-mPEG) was obtained through the conjugation of mPEG–PCL with hyper-branched PEI (hy-PEI) based on the Michael addition. mPEG–PCL was synthesized by ring-opening polymerization of caprolactone using mPEG as the initiator. Compared earlier syntheses, this method offered a reduced number of reaction steps, milder reaction conditions, and a more efficient purification process. FTIR, 1H NMR and 13C NMR spectra proved the structure of the copolymers and controllability of this new synthesis method. Using 1H NMR spectroscopy the degradation of these copolymers was evaluated. Cytotoxicity of copolymers and gene transfection efficiency of polyplexes displayed prominent composition dependence. Increasing the graft density of mPEG–PCL on hy-PEI and longer lengths of both PCL and mPEG within the copolymers investigated here reduced transfection and cytotoxicity on A549 cells. The hy-PEI-g-PCL-b-mPEG copolymers with very short PCL segments (342 Da and 570 Da) demonstrated 6-fold higher transfection efficiency than hy-PEI25k on A549 cells. The polyplexes of the most promising candidate, hy-PEI25k-g-(PCL570-b-mPEG2k)1, exhibited lower hemolysis compared to those of hy-PEI25k.