Heparin-modified PEI encapsulated in thermosensitive hydrogels for efficient gene delivery and expression

A strategy for efficient gene delivery and expression was developed by encapsulating complexes of plasmid DNA and heparin-modified polyethylenimine into thermosensitive dextran-poly(epsilon-caprolactone) 2-hydroxylethylmethacrylate poly(N-isopropylacrylamide) (Dex-PCL-HEMA-PNIPAAm) hydrogels. Thermosensitive hydrogels (THs) with different compositions were prepared and the TH with the highest content of PCL and Dex had the smallest pore size. Branched polyethylenimine (PEI) and heparin (Hep) could spontaneously form Hep/PEI complex particles in aqueous solution with the Hep content ranging from 20-50%. The Hep/PEI complex particles with 20% Hep (HP20), which were spherical in morphology, were well-dispersed and possessed a narrow size distribution with an average diameter of 209 nm. HP20/DNA complexes were then encapsulated in different THs. The release of HP20/DNA complexes from the hydrogels occurred mainly within the first 72 h in phosphate-buffered saline. HP20/DNA complexes used to transfect HeLa and 293T cells yielded luciferase expression levels which were 50-140-fold higher in serum-containing media, compared with PEI/DNA complexes in serum-free media. HP20/DNA complexes encapsulated in Dex-PCL-HEMA-PNIPAAm hydrogels not only exhibited appreciable transfection efficiency, but also provided a prolonged transgene expression, indicating that the combination of heparin-modified PEI and thermosensitive hydrogels has great potential for localized gene delivery.