“诊疗一体化”骨支架的仿生构建与骨再生的动态监测

The lack of sufficient vascularization at the defect site is a main limitation for clinical applications of tissue engineered bone. An important strategy to promote vascularization in bone regeneration is to delivery of key angiogenic and osteogenic growth factors in a spatiotemporal manner similar to the natural bone healing cascade. In order to mimic the dynamic microenvironment during bone regeneration, the scaffold design should be optimized according to the real-time data from in vivo animal experiments. As such, it is necessary to establish a noninvasive imaging technique that allows for dynamic, longitudinal and consistent monitoring of tissue-engineered bone constructs, which would be beneficial for developing optimized scaffold that provides a favourable microenvironment for successful bone regeneration. Therefore, this project proposed a concept of “theranostic bone tissue engineering”. In order to proof of this concept, the europium (Eu) and gadolinium (Gd) ions will be doped into a biodegradable mesoporous silica nanoparticles (BMSNs) structure to achieve the multomodality imaging capability including fluorescence, computed tomography (CT) and magnetic resonance (MR) imaging, while the osteogenic BMP-2-derived peptide (BMP-2P) and angiogenic small molecule (FTY720) will be covalently linked to the surface and the mesoporous channels of BMSNs. The developed multifunctional nanocarriers can be incorporated into Poly(L-lactide)/Polycaprolactone (PLLA/PCL) nanofibrous scaffolds by thermally induced phase separation (TIPS) technique, and thus constructing a multifunctional scaffold that integrates multimodality imaging and dual drug delivery capabilities for dynamic monitoring of bone regeneration process and bone healing. The aim of this study is to investigate the synergistic interaction of angiogenesis and osteogenesis during bone regeneration, which can provide valuable insight for promoting the successful vascularization of tissue engineered bones, thus facilitating its clinical translation.

血供不足是组织工程骨实现临床转化的主要障碍。模拟骨愈合过程中生长因子的级联响应模式，实现成骨和血管化因子的时空释放与表达，是解决血管化难题的重要手段。由于体内再生微环境的动态变化，支架设计应根据体内实验反馈的实时数据进行优化。因此，亟待建立一种非侵入性的骨再生动态监测技术，以优化支架设计并为骨修复提供适配的仿生微环境。本项目提出“诊疗一体化”骨组织工程概念，拟制备Eu3+/Gd3+双掺杂的生物可降解介孔硅纳米粒子，实现荧光/CT/MR多模态成像功能。通过表面接枝成骨短肽（BMP-2P）和内孔吸附血管化小分子（FTY720），实现成骨和血管因子的顺次释放。将纳米载体与PLLA/PCL三维多孔纳米纤维支架复合，构建具有双因子控释和多模态成像功能的骨支架。旨在通过多模态影像技术动态监测骨再生过程，揭示其中血管化与成骨的关系，为解决骨组织工程的血管化难题提供理论依据，并为其临床转化提供新的思路。

组织工程技术的临床应用仍十分有限。一个重要原因是传统方法主要依赖破坏性的组织学技术来获取信息，无法对同一实验个体进行连续的动态监测。因个体差异，反馈的信息难以反映真实的组织再生状况，设计的工程化组织因缺乏良好的生物适配性而失败。本项目以骨组织工程为范例，针对骨修复过程中成骨和血管化两大科学问题，将多因子控释和多模态影像技术（如荧光、CT 或MR 成像）整合到支架制备过程中，开发可采用非侵入影像技术动态监控组织再生过程的支架材料，实现对组织再生过程中支架降解、细胞生长、组织生成和血管长入等关键要素的动态可视化监控，以揭示各要素在组织修复中的协同作用，开发一种新型“可视化”组织工程技术。项目以介孔二氧化硅纳米粒子（MSNs）为载体，采用多种成骨因子和血管化因子的组合模式，构建成骨/血管化双因子程序释放体系，研究不同释放模式对骨的血管化和成骨的作用。针对骨再生环境难以动态监测的难题，采用镧系金属特殊成像性质，将Eu3+和Gd3+掺杂到MSNs中并与聚合物复合支架结合，探索骨再生过程中支架降解、细胞长入、血管发生和新骨生成等再生要素之间的关系。