钛基植入体自组装纳米胶束抗菌表面的构建及其应答式骨修复作用的研究

The implant loosening caused by the infection limits the clinic application of the titanium-based prosthesis. An antibacterial coating is one of the effective ways to attack bacteria around the prosthesis. As a potent antibacterial agent, the bioactive peptide LL-37 shows high capability to control cell function. It can induce the differentiation of the circulating monocytes into monoosteophils, which in turn initiate the controlled mineralization and accelerate the bone repair. The program focuses on the bone repair and restoration via an antibacterial and self-assembled nano capsule coating on the titanium-based prosthesis, based on our previous study about the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), the radical graft polymerization, the biomimetic mineralization and the cell encapsulation technique. These capsules are designed to be prepared by an amphiphilic copolymer containing the hydrophobic PHBV block coupling with the titanium-based implant and the hydrophilic chains on the surface of the nano capsule that will be grafted with the antibacterial peptide LL-37 chemically. The nano-sized capsules will increase the effective range of the concentration (or the grafting density) of LL-37 greatly, thus promising the differentiation of the monocytes into the monoosteophils. The effect of the structure, size or morphology of the nano capsule and the grafting density or distribution of the antibacterial peptides on the antibacterial properties will be studied. The scientific solution to the antibacterial mechanism of the antibacterial and self-assembled nano capsule coating and the controlled mineralization of the monoosteophils will be disclosed, as a theoretical framework for the bionic design of a bioactive and antibacterial coating for the titanium-based prosthesis via a responsive bone-repairing mechanism.

由细菌感染引发的植入体松动是困扰钛基假体的重要临床问题，抗菌涂层是假体抵抗细菌的重要手段之一。活性肽LL-37兼具抗菌性和细胞功能调节作用，能激活血液单核细胞诱导分化为成骨化细胞，参与调控生物控制矿化进程，加速植入体与机体骨性结合。在前期聚羟基烷酸酯、自由基接枝聚合、仿生矿化及细胞微囊化研究的基础上，本项目以应答式骨修复为核心，采用含疏水聚羟基烷酸酯的两亲嵌段共聚物自组装纳米胶束的结构设计，构建纳米胶束抗菌表面。两亲嵌段共聚物疏水端偶联植入体及胶束表面亲水端偶联LL-37的结构，将增大抗菌肽有效使用浓度（或接枝密度）区间，使抗菌肽能够诱导单核细胞分化为成骨化细胞。深入研究纳米胶束的结构、尺寸、形貌以及抗菌肽的接枝密度、分布对钛基植入体抗菌性的影响规律，阐明纳米胶束活性抗菌涂层的抗菌机制，揭示成骨化细胞的生物控制矿化机理，为具有应答式骨修复性的生物活性抗菌涂层的仿生设计提供科学依据。

抗菌涂层是解决植入体细菌感染的重要手段之一。多肽凭借亲水间隔臂化学键合于植入体表面，具抗菌性和细胞功能调节作用，加速植入体与机体结合。本项目基于嵌段共聚物自组装胶束或点击化学构建接枝多肽表面，有效调控多肽接枝密度，维持多肽构象。从聚羟基烷酸酯基两亲嵌段共聚物的合成出发，调控两亲嵌段共聚物的亲疏水片段组分和分子量，通过自组装方式制备了表面亲水的聚合物杆状胶束，修饰二维无机片层表面或与无机抗菌剂复合制备复合纳米胶束，具有良好的细胞相容性和抗菌性，其细胞相容性、抑菌和杀菌效果受嵌段共聚物中亲水链长所决定。以多肽为嵌段结构构建含有多肽的嵌段共聚物，或基于点击化学反应接枝多肽，可精准控制表面多肽的密度。在含有多肽的嵌段共聚物修饰表面，多肽嵌段结构的引入加速了共聚物体外水解、酶解以及体内的降解速率，但细胞增殖并无显著提高。多肽接枝嵌段共聚物表面具有良好的抗菌性、血液相容性、特异吸附性。多肽接枝未显著提高体外细胞增殖率，但体内明显加速肌纤维的再生。多肽与植入体表面间引入的亲水间隔臂，对蛋白吸附和细胞产生直接影响。亲水长链不利于蛋白黏附，能较好维持蛋白构象，但亲水修饰层的厚度改变表面弹性模量，对细胞的增殖、分化等行为产生影响，且不同细胞对表面弹性模量的响应亦不同。通过四年的研究探索，阐明了表面纳米胶束的结构、尺寸、形貌及多肽接枝密度和分布对抗菌性和细胞相容性的影响，揭示多肽表面特异性蛋白吸附规律，探讨多肽接枝层影响细胞粘附、增殖以及诱导细胞分化的作用机制，为多肽介导组织修复研究提供科学依据。