In vitro release of plasmid DNA from oligo(poly(ethylene glycol) fumarate) hydrogels

This research investigates the release of plasmid DNA in vitro from novel, injectable hydrogels based on the polymer oligo(poly(ethylene glycol) fumarate) (OPF). These biodegradable hydrogels can be crosslinked under physiological conditions to physically entrap plasmid DNA. The DNA release kinetics were characterized fluorescently with the PicoGreen and OliGreen Reagents as well as through the use of radiolabeled plasmid. Further, the ability of the released DNA to be expressed was assessed through bacterial transformations. It was found that plasmid DNA can be released in a sustained, linear fashion over the course of 45-62 days, with the release kinetics depending upon the molecular weight of the poly(ethylene glycol) from which the OPF was synthesized. Two formulations of OPF were synthesized from poly(ethylene glycol) of a nominal molecular weight of either 3.35K (termed OPF 3K) or 10K (termed OPF 10K). By the time the gels had completely degraded, 97.8 ± 0.3% of the initially loaded DNA was recovered from OPF 3K hydrogels, with 80.8 ± 1.9% of the initial DNA retaining its double-stranded form. Likewise, for OPF 10K gels, 92.1 ± 4.3% of the initially loaded DNA was recovered upon complete degradation of the gels, with 81.6 ± 3.8% of the initial DNA retaining double-stranded form. Experiments suggest that the release of plasmid DNA from OPF hydrogels is dominated by the degradation of the gels. Bacterial transformation results indicated that the DNA retained bioactivity over the course of 42 days of release. Thus, these studies demonstrate the potential of OPF hydrogels in controlled gene delivery applications.