Cell-free 3D scaffold with two-stage delivery of miRNA-26a to regenerate critical-sized bone defects

MicroRNAs ( miRNAs) are being developed to enhance tissue regeneration. Here we show that a hyperbranched polymer with high miRNA-binding affinity and negligible cytotoxicity can self-assemble into nano-sized polyplexes with a 'double-shell' miRNA distribution and high transfection efficiency. These polyplexes are encapsulated in biodegradable microspheres to enable controllable two-stage (polyplexes and miRNA) delivery. The microspheres are attached to cell-free nanofibrous polymer scaffolds that spatially control the release of miR-26a. This technology is used to regenerate critical-sized bone defects in osteoporotic mice by targeting Gsk-3b to activate the osteoblastic activity of endogenous stem cells, thus addressing a critical challenge in regenerative medicine of achieving cell-free scaffold-based miRNA therapy for tissue engineering.