基于免疫调变和力学完整设计的钛合金表层结构及其生物功能提升机制

Focusing on the controversy between the porous requirement of metallic material’s surface layer for biological functions and smooth requirement of the layer for mechanical integrity, and aiming at the plastic phenotypes of polarized microphages, the project plans to design novel immunomodulatory surface layers on Ti alloy, which consist of macroporous Ti alloy scaffolds, macropores’ walls adhered coatings composed of components-doped titania and nanorod arrays, and drug-loaded gelatin nanospheres on nanorod arrays. Noticeably, the nanorod arrays are constructed by ZnO, Zn-Mg-Sr titanate and multi-ions doped hydroxyapatite, respectively. To this end, we make an effort to establish key techniques for coating macroporous Ti alloy scaffolds on Ti alloy substrates and modification of macropores’ walls of the scaffolds. The research interests include: the bond strengthening mechanism of Ti-Ta solution between the macroporous Ti alloy scaffolds and Ti alloy substrates; the formation mechanism of the nanorod arrays, and bond strengthening mechanism of the interfaces between the coatings and Ti alloy walls as well as the bilayers in the coatings; the relationship between adhesion and polarized phenotypes of macrophages and porous parameters of surface layers as well as structural parameters and degradation behavior of the nanorod arrays, and their effect on the behavior of osteoblasts and mesenchymal stem cells; the effect of gelatin loading media on the recruiment and polarized phenotypes of macrophages, and its influence on bacteria cleaning; the efficiency and modulating mechasim of components-doped titania and nanorod arrays to surpress bacterial adhesion; the surpressing mechasim of aspect loosening by the ions released from the coatings. It is the aim to well highlight the modulatory mechanism of immune responses to the surface layers’ structure for promoting osseointegration, long-term bacterial resistance and surpressing aspect loosening, the mechanism that the corrosion fatigure of Ti alloy will be surpressed by the surface layers, and therefore establishing the fundamental of surface modification of metallic materials to improve their clinical functions.

针对生物功能要求金属植入体表层多孔与力学完整要求其光滑的矛盾，着眼于巨噬细胞（M）极化表型可塑，通过攻克赋予基体残余压应力、并与之以Ti-Ta固溶结合的钛合金多孔支架及其孔壁改性关键技术，为钛合金设计并构建由多孔钛合金支架、附于其孔壁的“组元掺杂氧化钛/纳米棒阵列”涂层、覆于纳米棒阵列的载药明胶纳米球构成的免疫调变表层。揭示支架与基体、涂层与支架孔壁及涂层层间结合的强化机制，表层孔隙参量、纳米棒阵列结构参量及降解行为与M附着及极化表型的关系，及其对成骨/基质干细胞行为和成骨化的调控机制；阐明明胶负载介质对M募集和极化表型的调控效应及其清理细菌的效应，氧化钛掺杂组元组态、纳米棒阵列化学组成和降解行为对细菌附着的抑制机制；揭示涂层释放离子对无菌松动的抑制机制。阐明表层结构提升骨整合、长效抗菌、抑制无菌松动等生物功能的免疫调变机制，抑制钛合金腐蚀疲劳的机制，为提升钛合金临床效能奠定表面改性基础。

针对钛合金植入体存在的骨整合能力弱、细菌感染、无菌松动、腐蚀疲劳断裂等临床问题，本项目围绕植入体表层结构设计与构建原理展开研究。采用表面机械研磨处理在钛合金基体表层形成了纳米晶及残余压应力，随之采用高能束3D打印技术构建了以Ti-Ta固溶体为过渡层的多孔钛合金支架，继而采用多种表面改性技术制备了一系列生物功能化涂层。通过工艺优化，基体表层及Ti-Ta固溶层中的残余压应力可显著抑制腐蚀疲劳裂纹萌生及扩展，提升植入体的腐蚀疲劳强度，并揭示了其机制。生物功能化涂层的化学组成和纳米棒阵列构形除了直接影响基质干细胞成骨行为及抑/杀菌行为以外，还可显著调控巨噬细胞（MΦ）的极化表型及其分泌的细胞因子等免疫响应，进而显著影响基质干细胞成骨行为、骨整合性、抗菌行为及无菌松动。阐明了单/多种离子掺杂钛酸钠、羟基磷灰石（HA）、TiO2和ZnO等纳米棒阵列化涂层及生物分子负载层等各层界面间的组态与结合机制，以及纳米棒阵列构形参量、离子/生物分子释放对MΦ表型的调控效应及机制。特别是，适宜尺度的纳米棒间距可促进MΦ由早期的促炎M1表型向后续的抑炎M2表型转变，释放的掺杂离子（Ca2+、Mg2+、Sr2+、Zn2+等）和时序性递送的生物分子（LPS、S1P）通过调控MΦ胞内Ca2+浓度和细胞膜上相应受体，促进其由M1向M2转变；MΦ在相应时段分泌的相应细胞因子通过促进内皮细胞和基质干细胞募集和功能提升，促进血管化骨再生及骨整合。再者，通过掺杂离子以促进HA纳米棒降解、强化组成相间界面结合以减少涂层释放微粒，显著抑制了MΦ的转录因子NF-κB激活和致炎细胞因子释放，进而减轻了无菌松动。另外，阐明了涂层的纳米棒力学刺破、组元(如Zn2+、Cu2+、抗菌肽等)杀菌、M1巨噬细胞吞噬杀菌等抗菌机制。本项目从巨噬细胞免疫调控和力学完整视角建立了钛合金表层结构设计的新原理，发表SCI期刊论文70篇（含影响因子>10的论文18篇），授权专利11项，毕业博士生14人、硕士生9人；部分成果获国家科技进步一等奖、陕西省科学技术一等奖各1项。