Objective The healing of osteoporotic fractures in the elderly patients is a difficult clinical problem. Currently, based on the internal fixation of fractures, the available drug treatments mainly focus on either inhibiting osteoclast function, such as bisphosphonate, calcitonin, oestrogen or promoting osteogenesis, such as parathyroid hormones. However, the availability of current antiosteoporotic drugs in promoting osteoporotic fracture healing is limited. The objective of the present study was to investigate the ability of the MiR-21/nanocapsule to enhance the early bone repair of osteoporotic fractures. Methods Based on the presence of matrix metalloproteinases that are overexpressed at the fracture site, we designed the matrix metalloproteinase–sensitive nanocapsules which were formed by in situ free radical polymerisation on the surface of MiR-21 with 2-(methacryloyloxy) ethyl phosphorylcholine and the bisacryloylated VPLGVRTK peptide. The MiR-21/nanocapsule [n (miR-21)] and O-carboxymethyl chitosan (CMCS) were mixed until they formed a gel-like material [CMCS/n (miR-21)] with good fluidity and injectability. Thirty elderly Sprague Dawley (SD) rats (female, 14-month-old, 380 ± 10 g) were subjected to bilateral removal of the ovaries (ovariectomised). All rats were subjected to bilateral bone defects (2 mm diameter) of the proximal tibia and randomly divided into three groups (groups A, B, and C): separately injected with CMCS/n (miR-21), CMCS/n (NC-miR), and saline. Micro-computed tomography (CT) imaging was performed to evaluate newly formed bone volume and connectivity. Nondecalcified histology and toluidine blue staining were performed to measure the effects of CMCS/n (miR-21) on bone repair. In vitro, the effect of n (miR-21) on osteogenic differentiation to bone marrow mesenchymal stem cells (BMSCs) which derived from the ovariectomised rat model was observed. Results The morphology of n (miR-21) was a regular spherical nanocapsule with a uniform small size (25–35 nm). The results confirmed that n (miR-21) could be efficiently phagocytosed by BMSCs and released in the cytoplasm to promote osteogenesis. The expression level of alkaline phosphatase and Runt-related transcription factor 2 mRNA in the n (miR-21) group was higher than that in the n (NC-miR) group. Animal experiments proved that CMCS/n (miR-21) produced better bone repair compared with the CMCS/n (NC-miR) group in the early stages of fracture healing at 4 weeks. In the late stage of fracture healing (8 weeks), micro-CT quantitative analysis showed that the new bone trabeculae in the CMCS/n (miR-21) group has decreased compared with the CMCS/n (NC-miR) group. In the CMCS/n (miR-21) group, the new cancellous bone had been absorbed, and the process of bone healing was almost completed. In contrast, the new bone in the CMCS/n (NC-miR) and the control groups was still in the healing process. Conclusion The cytological tests confirmed that n (...

Taking the advantages of the unique physiological character of bone fracture, a systemic delivery platform of growth factors for bone repair based on nanocapsules was exploited.

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The extreme instability of mRNA makes the practical application of mRNA-based vaccines heavily rely on efficient delivery system and cold chain transportation. Herein, a DNA-based nanomachine, which achieves programmed capture, long-term storage without cryopreservation, and efficient delivery of mRNA in cells, is developed. The polythymidine acid (Poly-T) functionalized poly(N-isopropylacrylamide) (DNA-PNIPAM) is synthesized and assembled as the central compartment of the nanomachine. The DNA-PNIPAM nano-assembly exhibits reversible thermal-responsive dynamic property: when lower than the low critical solution temperature (LCST, ≈32 °C) of PNIPAM, the DNA-PNIPAM transforms into extension state to expose the poly-T, facilitating the hybridization with polyadenylic acid (Poly-A) tail of mRNA; when higher than LCST, DNA-PNIPAM re-assembles and achieves an efficient encapsulation of mRNA. It is remarkable that the DNA-PNIPAM nano-assembly realizes long-term storage of mRNA (≈7 days) at 37 °C. Biodegradable 2-hydroxypropyltrimethyl ammonium chloride chitosan is assembled on the outside of DNA-PNIPAM to facilitate the endocytosis of mRNA, RNase-H mediating mRNA release occurs in cytoplasm, and efficient mRNA translation is achieved. This work provides a new disign principle of nanosystem for mRNA delivery.