Investigation of oligo(poly(ethylene glycol) fumarate) hydrogels for controlled release of plasmid DNA

Hydrogels of oligo(poly(ethylene glycol) fumarate) (OPF) were investigated toward the controlled release of therapeutic plasmid DNA for tissue engineering applications. The release of DNA from OPF hydrogels and the swelling characteristics of the hydrogels were characterized in vitro. The results demonstrated that the nominal molecular weight of the poly(ethylene glycol) from which the OPF was synthesized affects the hydrogel swelling and the DNA release kinetics. Further, these studies indicated that the degradation of the OPF dominates the control of DNA release. The retention of DNA bioactivity over the course of release was demonstrated through bacterial transformations. Subsequent studies characterized the release of plasmid DNA from composites of OPF and cationized gelatin microspheres (CGMS) in vivo, as well as the degradation kinetics of CGMS in these composites. Comparisons between the composite groups and material control groups indicated that the bioavailability of DNA can be extended through release from CGMS encapsulated within OPF, relative to CGMS or DNA solution injection alone, although no difference was observed between the composites and OPF. A related study characterized the release of DNA from the composites of OPF and CGMS in vitro. The results demonstrated that plasmid DNA can be released in a sustained fashion over the course of 49 to 149 days, with the release kinetics depending upon the material composition and the method of DNA loading. Released DNA retained viable structure over the course of release. A final study investigated the release of plasmid DNA encoding an osteogenic protein from composites of OPF and CGMS toward enhancing bone regeneration in a rat calvarial defect model. No enhancement in new bone formation was observed with release of DNA, relative to material controls. However, the reason for the absence of enhancement could not be elucidated in the study. Thus, hydrogels of OPF and composites of OPF and CGMS demonstrate potential as tissue engineering scaffolds for the controlled release of plasmid DNA, yet further investigation is warranted to assess transfection efficiency and gene expression with these systems.