Abstract: Objective To prepare insulin-loaded polymeric nanoparticles based on polyethyleneimine-polycaprolactonepolyethylene
glycol-polycaprolactone-polyethyleneimine pentablock copolymers and evaluate its in vitro release of insulin.
Methods Polycaprolactone-polyethylene glycol-polycaprolactone (PCL-PEG-PCL) triblock copolymer was synthesized by
ring-opening polymerization method, and the pentablock copolymer was prepared by Michael addition reaction. The
copolymers obtained were characterized by Fourier-transform infrared (FT-IR) spectroscopy and 1H-NMR and their critical
aggregation concentration (CAC) was measured by fluorescence technique with pyrene as the probe. Insulin-loaded polymeric
nanoparticles based on the pentablock copolymers were prepared by solvent evaporation method that exploited the cationic
nature of PEI-PCL-PEG-PCL-PEI to allow the formation of ionic complexes with anionic biomolecules such as insulin. The
prepared nanoparticles were further characterized by Malvern laser particle sizer and transmittion electron microscopy (TEM).
The drug loading, encapsulation efficiency and in vitro release profile of the nanoparticles were analyzed using Bradford
method. Results Using copolymer PEI10K-PCL4K-PEG2K-PCL4K-PEI10K as the drug carrier, the spherical nanoparticles
prepared with an optimal insulin-coplymer mass ratio of 40% allowed the maximum insulin loading of (18.63±0.07)% and had
an average particle size of 175.30±19.51 nm. The prepared nanoparticles was capable of sustained release of insulin for as long
as 48 h in vitro, and the burst release could be minimized by incorporation of PEI in the triblock copolymer. Conclusion The
insulin-loaded polymeric nanoparticles based on the pentablock copolymers allow sustained release of insulin in vitro, and PEI
can enhance sustained drug release and reduce burst drug release.