Fig. 5

Two-stage delivery of miRNA-26a from scaffold repaired critical bone defects. a Schematic illustration of the two-stage miRNA delivery system. The miRNA and gene vector formed polyplexes in water, which were encapsulated into PLGA microspheres, followed by immobilization onto the PLLA scaffold. The implanted scaffold filled in the mouse calvarial defect. The PLGA microspheres released miRNA–vector complex or polyplexes in vivo and the polyplexes were taken into cells through endocytosis. Once inside the cell, the intracellular release of miRNA regulated subsequent gene expression. b Release profiles of miRNA from different PLGA (6.5 or 64 kDa) microspheres containing different gene/vector complexes (LP or HP). The release durations (short and long) were controlled by tuning the polymer matrix. c Representative µCT and H&E analysis of scaffolds in the mouse critical defect model. (a) Cell-free scaffold with the NC polyplexes (miR-26a-bolus or NC-bolus) or miRNA-26a/HP vector polyplexes bolus; (b) cell-free scaffold with short-term releasing PLGA microspheres that contains the NC polyplexes (miR-26a-bolus or NC-bolus) or miRNA-26a/HP vector polyplexes; (c) cell-free scaffold with long-term releasing PLGA microspheres that contains the NC polyplexes (miR-26a-bolus or NC-bolus) or miRNA-26a/HP vector polyplexes. Results showed that the two-stage delivery of miRNA-26a repaired the critical calvarial bone defect in vivo and the long-term sustained release was much more advantageous than the short-term release. Scale bars, 5 mm (in μCT images), 2.0 mm (in H&E images at right), 200 mm (in higher-mag H&E images at far right). Copyright © 2016 by Nature Publishing Group, reprinted with permission of Nature Publishing Group, from Zhang et al.⁵⁰