如何有效地利用生物材料促进大段骨缺损的再生与修复，是现代组织工程医学研究的热点和难点。近期研究发现，体内骨组织再生是由血凝块、免疫系统以及骨组织共同调节和作用的结果。创伤后形成的血凝块是骨再生与修复的始发中心，其结构和功能对局部骨免疫反应具有调节作用，是决定骨组织能否再生的关键因素。本项目拟研制APT-NPs-TCP血小板活性生物材料，选择性诱导功能性血凝块的形成，以促进大段骨缺损的修复与再生。首先通过研究体内不同大小骨缺损处血凝块的结构/功能以及对局部免疫和骨再生的影响，指导合成人工血小板-纤维蛋白-凝血酶纳米微球复合物（APT-NPs）以促进传统生物支架表面功能性血凝块的形成，然后通过体内外实验研究该支架诱导凝血的效果和对血凝块结构/性状的调节，以及其进一步对骨免疫和骨再生的调节作用，从而阐明血凝块-免疫-骨组织之间的交互作用以及成骨机理，为生物材料在大段骨再生的临床应用提供新思路。

Treatment of large bone defects remains a significant challenge in daily dental and orthopedic clinics and most treatments require the intervention using bone substitute biomaterials. Accumulating evidences indicate that bone healing is not a simple process of osteoblasts, instead it involves complicated interactions between immune and skeletal systems. For example, the post-injury hematoma (blood clot in bone healing), which not only serves as the natural scaffold for stem cell proliferation and differentiation; but also regulates the local immune cells to modulate osteogenesis, plays an element role in bone repair. Therefore, desired bone substitutes should be able to regulate hematoma properties, leading to favorable osteoimmune regulation and bone regeneration. This proposed study is to design and synthesize artificial platelet-rich fibrin-thrombin nanocapsules (APT-NPs) to achieve control-release of thrombin for bone healing hematoma formation and control osteoimmune reaction for bone regeneration. .In the current study, the structure, function and histologic difference of bone healing hematoma will be characterized using the healing and non-healing bone segmental defects (1 mm and 5 mm defects in rat femur). The correlations between bone hematoma and local osteoimmune reaction will be analyzed to understand the mechanisms under blood clot-mediated initial bone healing processes. The findings will guide the design and synthesis of a nanocapsule-based system, which will be used to achieve control-release of thrombin. The coating of platelet-rich fibrin (PRF) on the nanocapsule surface will create the artificial PRF-thrombin nanocapsules (APT-NPs). APT-NPs will then be used to improve the traditional β-TCP scaffolds (APT-NPs-TCP). The hematoma formation, osteoimmune regulation and osteogenesis of APT-NPs-TCP will be investigated via the characterization of blood clot properties, macrophage activation/polarization, mesenchymal stem cell migration/osteogenic differentiation. The osteogenesis of APT-NPs-TCP will be assessed via the transplantation of APT-NPs-TCP scaffolds in the rat large bone defects. Taken together, this study will systemically unveil the ultimate mechanisms of early bone healing processes by investigation of bone hematoma and osteoimmunomodulation, which will guide the design of bone biomaterials for early intervention and bone regeneration to healing large bone defects. This project will develop a novel strategy for translational bone biomaterials development.