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.