Background: Treatment of large bone defects represents a major clinical problem worldwide. Suitable bone substitute materials are commonly required to achieve successful bone regeneration, and much effort has been spent to optimize their chemical compositions, 3D architecture and mechanical properties. However, material-immune system interactions are increasingly being recognized as a crucial factor influencing regeneration. Here, we envisioned an accurate and proactive immunomodulation strategy via delivery of IL-4 (key regulator of macrophage polarization) to promote bone substitute material-mediated regeneration.

This study aimed to investigate the radiosensitizing effect of polydatin (PD) on colorectal cancer (CRC) and its underlying mechanism. The C57BL/6 mouse model of CRC was induced by treatment with azoxymethane (AOM)/dextran sodium sulfate (DSS) and then divided into four groups: control, PD alone, IR alone, and combination of PD and IR. Radiation therapy (200 cGy/min, 10Gy) was performed in mice in the experimental groups for once a week with a total of four times. Thirty minutes before IR, mice were intraperitoneally injected with PD at the dose of 25mg/kg. The number and volume of CRC xenografts were calculated. Immunohistochemical staining was performed to detect the expression of Ki67 and cleaved caspase-3 in tumor tissues samples. The effects of PD on proliferation and apoptosis were evaluated in CT26 and HCT116 colon tumor cells. Leucine-rich repeat-containing G-protein coupled receptor 5 positive (Lgr5⁺) cancer stem cells (CSCs) were sorted from CT26 cells and the effects of PD on their proliferation and apoptosis were observed to elucidate the radiosensitizing mechanism of PD in CRC cells. Combined therapy with PD and IR significantly decreased tumor volume, inhibited proliferation and induced apoptosis of tumor cells in the mouse model of CRC compared to other three groups. Compared to the IR group, in vitro assay showed that PD combined with IR inhibited proliferation and promoted apoptosis of CT26 and HCT116 colon tumor cells as well as Lgr5⁺ CSCs. However, addition of the bone morphogenetic protein (BMP) type I receptor inhibitor K02288 (6.4nM) dramatically increased proliferation of Lgr5⁺ CSCs and abolished the cytotoxic effect of PD combined with IR on Lgr5⁺ CSCs. The in vivo and in vitro experiments demonstrated that IR combined treatment with PD could inhibit proliferation and promote apoptosis of CRC cells and Lgr5⁺ CSCs, and BMP signaling pathway was involved in the radiosensitizing effect of PD.

Bone tissue engineering is not widely used in clinical treatment. Two main reasons hide behind this: (1) the seed cells are difficult to obtain and (2) the process of tissue engineering bone construction is too complex and its efficiency is still relatively low. It is foreseeable that in the near future, the problem of seed cell sources could be solved completely in tissue engineering bone repair. As for the complex process and low efficiency of tissue engineering bone construction, usually two strategies would be considered: (1) the construction strategy based on injectable bone tissue and (2) the construction strategy based on osteogenic cell sheets. However, the application of injectable bone tissue engineering (iBTE) strategy and osteogenic cell sheet strategy is limited and they could hardly be used directly in repairing defects of large segmental bone, especially load-bearing bone. In this study, we built an osteogenic micro-tissue with simple construction but with a certain structure and composition. Based on this, we established a new iBTE repair strategy—osteogenic micro-tissue in situ repair strategy, mainly targeting at solving the problem of large segmental bone defect. The steps are as follows: (1) Build the biodegradable three-dimensional scaffold based on the size of the defect site with 3D printing rapid prototyping technology. (2) Implant the three-dimensional scaffold into the defect site. This scaffold is considered as the “steel framework” that could provide both mechanical support and space for bone tissue growth. (3) Inject the osteogenic micro-tissue (i.e., the “cell-extracellular matrix” complex), which could be considered as “concrete,” into the three-dimensional scaffold, to promote the bone tissue regeneration in situ. Meanwhile, the digested cells were injected as the compared group in this experiment. After 3 months, the effect of in situ bone defect repair of osteogenic micro-tissue and digested cells was compared. It is confirmed that osteogenic micro-tissue could achieve a higher efficiency on cell usage and has a better repair effect than the digested cells. Osteogenic micro-tissue repairing strategy would be a more promising clinical strategy to solve the problem of large segmental bone defect.