Yen-Chen Huang

Bone regeneration in a rat cranial defect with delivery of PEI-condensed plasmid DNA encoding for bone morphogenetic protein-4 (BMP-4)

Gene therapy approaches to bone tissue engineering have been widely explored. While localized delivery of plasmid DNA encoding for osteogenic factors is attractive for promoting bone regeneration, the low transfection efficiency inherent with plasmid delivery may limit this approach. We hypothesized that this limitation could be overcome by condensing plasmid DNA with nonviral vectors such as poly(ethylenimine) (PEI), and delivering the plasmid DNA in a sustained and localized manner from poly(lactic-co-glycolic acid) (PLGA) scaffolds. To address this possibility, scaffolds delivering plasmid DNA encoding for bone morphogenetic protein-4 (BMP-4) were implanted into a cranial critical-sized defect for time periods up to 15 weeks. The control conditions included no scaffold (defect left empty), blank scaffolds (no delivered DNA), and scaffolds encapsulating plasmid DNA (non-condensed). Histological and microcomputed tomography analysis of the defect sites over time demonstrated that bone regeneration was significant at the defect edges and within the defect site when scaffolds encapsulating condensed DNA were placed in the defect. In contrast, bone formation was mainly confined to the defect edges within scaffolds encapsulating plasmid DNA, and when blank scaffolds were used to fill the defect. Histomorphometric analysis revealed a significant increase in total bone formation (at least 4.5-fold) within scaffolds incorporating condensed DNA, relative to blank scaffolds and scaffolds incorporating uncondensed DNA at each time point. In addition, there was a significant increase both in osteoid and mineralized tissue density within scaffolds incorporating condensed DNA, when compared with blank scaffolds and scaffolds incorporating uncondensed DNA, suggesting that delivery of condensed DNA led to more complete mineralized tissue regeneration within the defect area. This study demonstrated that the scaffold delivery system encapsulating PEI-condensed DNA encoding for BMP-4 was capable of enhancing bone formation and may find applications in other tissue types.

Delivery of PEI-condensed DNA via a porous polymer scaffold for tissue engineering applications

An attractive approach to tissue engineering is the delivery of therapeutic plasmid DNA through biodegradable polymers. However, the low transfection efficiency of naked DNA might be a limitation. Poly(ethylenimine) (PEI) has been shown to be highly effective as a non-viral gene delivery vehicle and we hypothesized that local delivery of condensed DNA in a three dimensional biodegradable scaffold will enhance transfection efficiency compared to that of uncondensed DNA. To address this, we optimized the characteristics of PEI-DNA condensates encapsulated within PGLA sponge formed by a gas foaming process and performed in vitro transfection studies. Release of uncondensed DNA from sponges was rapid, while release was significantly slower when condensed DNA was incorporated. In vitro transfection was observed only in sponges incorporating condensed DNA, while no transfection was observed for sponges incorporating uncondensed DNA. This study demonstrates the feasibility of incorporating freeze-dried PEI-DNA condensates within PLGA sponges using sucrose as the pore forming agent to efficiently transfect cells, and may find application in areas such as bone tissue engineering.