超临界发泡制备聚羟基乙酸及其共聚物三维支架过程的复杂相互作用及调控

Degradable polymeric biomaterials are preferred candidates for developing therapeutic devices as temporary prostheses and three-dimensional scaffolds for tissue engineering. The features of scaffold should have excellent biocompatibility, controllable porous structure and biomechanical properties to provide efficient therapy for human cells to behave in seeding and attachment, proliferation, migration and differentiation into the specific tissues and organs. .Polyglycolic acid (PGA) is one of the first biodegradable synthetic polymer investigated for biomedical applications. As its high crystallinity, it is difficult to obtain PGA porous scaffolds with tunable porosity and pore size as well as distribution by conventional scaffold fabrication techniques. Foaming process using supercritical carbon dioxide (CO2) as physical blowing agent is an emerging green foaming technology to produce porous polymeric foams with different three-dimensional structures. .In this project, the dissolubility, plasticization and diffusion behaviors of ScCO2 on neat PGA and its co-polymer matrix, as well as the state of aggregation structure evolution, are to be fully investigated with Magnetic Suspension Balances(MSB) and Differential Scanning Calorimetry (DSC). Then the foamable range of neat PGA and its co-polymer matrix will be determined by the further investigation on bubble nucleation and growth during the batch foaming process using online micro-display system. Based on the complex interaction between ScCO2 and polymer and the interphase behaviors in the foaming process, a new foaming strategy and tuning the arguments for PGA scaffolds manufacture using supercritical carbon dioxide will be developed. Then the influence of foaming temperature and pressure on three-dimensional morphology, connectivity, biocompatibility and biomechanical properties will be evaluated. Furthermore, different kinds of micro/nano functional fillers, such as hydroxyapatite, β-TCP and TPP, will be used to make PGA composites foams. The morphology and the dispersion behavior of PGA matrix will be analyzed. The thermal behavior, the solution diffusion behavior and the induced crystallization behavior of PGA composites in ScCO2 will be studied in detail. Then the melt foaming process for PGA composites will be carried out to study the heterogeneous nucleation, bubble growth and coalescence behavior by using online micro-display visual autoclave. The porous structures and the mechanical properties of PGA scaffolds will be optimized. The cellular compatibility will then be assessed by attachment and proliferation of human fibroblasts..These fundamental work can contribute to produce the PGA composite scaffolds by a novel melt foaming process using ScCO2 with controllable porous structure and biomechanical properties. The result will be of great theoretical and practical importance for other supercritical fluid assisted polymer processing.

理想的支架材料应具备优良的生物相容性，可控的多孔三维结构以及良好的材料-细胞界面等特性。本项目针对高结晶度聚羟基乙酸及其共聚物，采用超临界CO2辅助的熔融发泡新方法，制备微纳结构可控、力学及生物性能优良的组织工程支架材料。项目拟充分研究超临界环境下PGA及其共聚物的塑化行为及聚集态结构演变、CO2在聚合物中的溶解-扩散行为以及气泡成核-生长-聚并的复杂相界面行为，以此为基础设计合理的PGA超临界发泡策略并实施发泡过程研究，揭示发泡过程非等温结晶与气泡成核的耦合作用机制，获得气泡成核-生长-聚并过程的关键调控手段；进一步通过添加HA、β-TCP、TPP等微纳功能填料，增强超临界流体在静态熔体中的溶解、扩散和结晶行为，改变气泡成核机制，促进过程异相成核，最终建立PGA/ScCO2/微纳填料三元交互作用下非等温结晶与异相成核过程的耦合机制，实现超临界环境下PGA三维支架的可控制备。

理想的组织工程支架材料应具备优良的生物相容性，可控的多孔三维结构以及良好的材料-细胞界面等特性。聚羟基乙酸（PGA）及其共聚物是性能优良的生物可降解聚酯材料，但因其结晶度高、溶解性差等问题，限制了其作为组织工程支架材料的应用发展。.本项目针对聚羟基乙酸及其共聚物，充分研究了PGA及其共聚物的聚集态、流变等行为以及与超临界CO2间的相互作用，进而以超临界CO2为绿色发泡剂，设计了“升温熔融-降温饱和-快速泄压”的熔融发泡新策略，系统考察了聚合物分子链结构特征、发泡温度、压力等条件对于多孔材料结构与性能的影响，成功制备了具有大孔径、高连通性和高模量的系列PGA、PLGA多孔支架材料。 .通过荧光表征等技术分析考察了PGA支架材料体外和体内降解行为，并基于特征孔结构对降解低聚物扩散行为的影响，建立了多孔聚酯支架的降解动力学模型，实现了大孔径高连通的多孔聚酯支架降解行为的模拟。此外，通过细胞实验和组织学分析，辨析了PGA支架的降解酸性微环境对巨噬细胞及其相关因子表达的影响，发现多孔PGA支架降解产物在支架内部快速积累，酸化了支架材料微环境，严重抑制了巨噬细胞的活性和分泌功能，引起较强炎症反应。.因此，通过引入功能性TPP微米颗粒和介孔生物玻璃MBG，分别调控了PGA和PLGA的发泡行为、支架微观形貌和生物相容性，制备了泡孔结构和生物性能优异的PGA-TPP、PLGA-MBG复合多孔支架材料。其中PGA-2 %TPP复合发泡支架可有效地中和支架降解酸性微环境，上调了巨噬细胞抗炎因子的表达，2周后可促进巨噬细胞向促修复的M2c表型极化，有效减少炎症细胞浸润，4周后多核巨细胞数量降低了24 %，减弱了异物反应程度，显著提升了PGA发泡支架的生物相容性。而15 wt%MBG复合的PLGA可制备大孔径高连通MBG/PLGA复合多孔支架，压缩强度达2.1 MPa，降解过程中可释放含钙离子及含硅离子，促进了骨髓干细胞MSCs在复合支架上的增殖和粘附，3周后改性PLGA支架ARS活性提升一倍以上，显著提升了PLGA多孔支架材料的体外成骨能力。.本项目针对PGA基生物可降解聚酯，通过创新的超临界发泡方法成功制备了大孔径高连通性的系列多孔组织工程支架，并优化了支架材料的多孔结构、降解性能与生物相容性，相关工作有望推动聚酯类组织工程支架材料的临床应用。