Research in bone tissue engineering aims to design materials that are effective at generating bone without causing significant side effects. The osteogenic potential of combining matrices and protein growth factors has been well documented, however, improvements are necessary to achieve optimal therapeutic benefits upon clinical translation. In this article, rat calvarial defects were treated with gene-activated matrices (GAMs). The GAMs used were collagen sponges mineralized with a simulated body fluid (SBF) containing a nonviral gene delivery system. Both in vitro and in vivo studies were performed to determine the optimal mode of gene delivery. After 6 weeks, the defects were extracted to assess bone formation and tissue quality through histological and microcomputed tomography analyses. The optimal GAM consisted of a collagen sponge with polyethylenimine plasmid DNA (PEI-pDNA) complexes embedded in a calcium phosphate coating produced by SBF, which increased total bone formation by 39% compared with 19% for control samples. A follow-up in vivo study was performed to optimize the ratio of growth factors included in the GAM. The optimal ratio for supporting bone formation after 6 weeks of implantation was five parts of pBMP-2 to three parts pFGF-2. These studies demonstrated that collagen matrices biomimetically mineralized and activated with plasmids encoding fibroblast growth factor-2 (FGF-2) and bone morphogenetic protein-2 (BMP-2) can optimally improve bone regeneration outcomes. Impact statement Bone tissue engineering has explored both nonviral gene delivery and the concept of biomimetic mineralization. In this study, we combined these two concepts to further enhance bone regeneration outcomes. We demonstrated that embedding polyethylenimine (PEI)-based gene delivery within a mineral layer formed from simulated body fluid (SBF) immersion can increase bone formation rates. We also demonstrated that the ratio of growth factors utilized for matrix fabrication can impact the amount of bone formed in the defect site. This research highlights a combined approach using SBF and nonviral gene delivery both in vitro and in vivo and prepares the way for future optimization of synthetic gene activated matrices.
Keywords: calvarial defect model; gene therapy; polyethylenimine; simulated body fluid; tissue engineering.