【作者】 曹宁；

【导师】 李木森；

【作者基本信息】 山东大学 ， 材料学， 2010， 博士

【摘要】 碳／碳复合材料具有碳材料固有的优异生物相容性,同时还具有与人体骨十分接近的弹性模量、稳定的化学性质和高强质轻的特点。但是,碳／碳复合材料单独作为硬组织修复和重建材料仍存在不能与骨组织形成化学结合、长期植入生物体内易产生“黑肤效应”和与人体骨组织的颜色差别较大等不足。为了避免因碳／碳复合材料表面碳颗粒剥落造成性能下降,同时提高其生物活性,人们采用多种技术手段在其表面制备生物活性涂层。羟基磷灰石(HA)因其具有优异的骨组织相容性和生物活性而被广泛用于制备人工骨材料的表面生物活性涂层。本文针对医用碳／碳作为骨组织重建和修复材料使用中存在的生物惰性、与自体骨色差较大、表面碳颗粒易脱落等不足,利用等离子体喷涂、表面仿生活化、反应烧结和射频等离子体辅助化学气相沉积(RF-FECVD)等技术在碳／碳复合材料表面制备了HA、SiC和类金刚石碳(DLC)等多种生物涂层,开展了制备工艺参数优化、涂层组织结构和性能表征。同时,按照临床应用的要求,对碳／碳复合材料的成分、显微结构、硬度、摩擦学性能和生物相容性进行了检测和分析。在此基础上开发出新型C／C+HA涂层复合材料种植体。通过体内种植和体外模拟实验,并对照粘胶基碳／碳复合材料的骨内植入实验结果,利用组织病理学和X射线透视等手段,评价了HA涂层对碳／碳复合材料的生物活性改善情况和植入材料与其周围生物组织的界面结合机理。研究表明,采用的碳／碳复合材料所含杂质经过检测均符合植入材料的要求,具有与人体骨接近的表面显微硬度。2400℃×2h的石墨化处理不仅提高了材料的石墨化程度,而且可明显降低碳／碳复合材料中的主要杂质元素含量。力学性能测试发现,碳／碳复合材料具有典型的复合材料应变率效应,其中的增强碳纤维具有阻止裂纹萌生和扩展的作用,克服了传统单质碳材料作为生物医用材料应用时脆性大的不足,提高了使用安全性。粘胶基碳／碳复合材料具有较低的摩擦系数。作为骨替换和修复材料与生物组织组成摩擦副时,该材料因微动磨损造成的表面碳颗粒脱落现象可能较轻。该材料具有多孔的表面结构,有利于细胞在材料表面形成直接黏附、增殖和分化,进而获得高密度的新生骨组织矿化结构和较高的界面结合强度。胫骨缺损的粘胶基碳／碳复合材料髓内固定动物实验表明,实验动物愈后恢复良好,骨缺损区骨组织改建基本完成。免疫组化分析未见因材料毒性引发的排异反应,从而在生物分子水平上证实了该材料具有的良好组织相容性,是一种具有较高临床应用价值的骨缺损修复材料。通过等离子体喷涂HA涂层剪切实验和对热处理前、后的HA涂层表面形貌、相组成和断口形貌分析发现,经700℃×10min热处理后,HA涂层的残余应力和微观结构的非均匀性得以改善。涂层的结晶度、纯度以及涂层／基体的界面结合强度均有所提高。但HA涂层与碳／碳复合材料界面元素扩散不明显,两者界面结合仍是以物理嵌合方式为主。因而可以认为,碳／碳复合材料的粗糙度、多孔表面形态是影响与HA涂层结合的主要因素。对碳／碳复合材料表面等离子体喷涂HA涂层的体内外生物学性能研究发现,HA涂层在体液环境中存在α-TCP、TTCP以及HA非晶相溶解和新生矿化HA的形核并长大。该过程不仅优化了HA涂层结构,而且涂层降解产物可为新生骨组织的形成提供适宜的生理环境,具有良好的引导新骨形成的作用。实验动物国内植入实验中,通过对照纯碳／碳复合材料表面组织改建情况可知,HA涂层不仅减轻了碳颗粒脱离对周围组织的染黑,而且改变了生物惰性材料表面软组织内化成骨的组织改建模式。骨细胞通过在HA涂层降解形成的Ca、P元素富集区内分化和增殖获得新生骨组织与涂层的直接界面结合。对碳／碳复合材料进行的表面仿生活化处理中,通过浓硝酸预氧化处理可将碳／碳复合材料表面少量氢键转化为羟基等含氧官能团。随后,在37℃恒温模拟体液浸泡条件下,新生类骨HA分子结构中的羟基可与预氧化处理获得的碳／碳复合材料表面羟基发生缩聚反应,从而形成化学键合,以“桥连”的界面结合方式获得较高的界面结合强度,改善了碳／碳复合材料的表面生物活性。通过Si粉包覆和反应烧结在碳／碳复合材料表面改性,获得了预期的SiC改性层,有利于减轻碳／碳复合材料表面碳颗粒的脱落现象,为开展SiC作为医用碳／碳复合材料的防护层或生物过渡层研究做了初步探索。对采用RF-PECVD方法制备的DLC薄膜进行组织结构和性能表征发现,碳源气体种类是影响DLC薄膜材料品质的关键。随着沉积时间的延长,薄膜组成颗粒不断长大,薄膜表面粗糙度随之提高。在CH4与Ar流量比1：20,射频电压1700V,电流0.45A,沉积时间2h条件下,可获得厚度均匀、具有较高sp3碳原子含量与表面硬度、较好的表面疏水性、较低的表面摩擦系数和优良综合机械性能的DLC薄膜。在抛光的PAN基碳／碳复合材料表面制备DLC薄膜的实验结果表明：DLC薄膜在碳／碳复合材料表面形成时,存在依附材料中原有热解碳非均匀形核和真空等离子体条件下的均匀形核两种成膜机制。获得的DLC薄膜显微形貌受碳／碳复合材料的表面结构影响较大。由于DLC自身结构致密,其在减轻医用碳／碳复合材料表面碳颗粒脱离和作为其他生物活性涂层的过渡层方面将具有潜在的应用价值。更多还原

【Abstract】 Carbon/carbon composites (C/C) are characterized by excellent biocompatibility, very similar elastic modulus to human bone and fine chemical stability. Also, they possess fine mechanical properties that are suitable for artificial bone. However, as hard tissue restoration and reconstruction materials, these materials have a few drawbacks. Firstly, carbon/carbon composites can not form chemical bond with human bone tissue due to their bioinert property. Secondly, the surface of unprocessed carbon/carbon is hydrophobic, so if it is put into the human body for a long time, the nomadic carbon will flow with the body fluid. Thirdly, the color difference between C/C and human bone is obvious. In order to avoid the decline of the mechanical properties due to the shedding of the surface carbon particles and enhance the bioactivity, people have prepared several biomedical coatings on C/C in different ways. Among these coatings, hydroxyapatite (HA) coatings have been broadly used as bioactive ones on artificial bone materials for their excellent biocompatibility and bioactivity. In the present work, HA, SiC, Diamond like carbon (DLC) coatings were prepared on the materials by means of plasma spraying, surface biomimetic activation, reaction sintering and radio frequency plasma enhanced chemical vapor deposition technologies. The technical parameters optimization of coating preparation, structure and property characterization of the coating were carried out. Meanwhile, according to the demand of clinic application, the constituent, microstructure, hardness, triological behaviors and biological behaviors of C/C were studied. By plasma spraying HA coatings on C/C, C/C+HA coated composite implants were developed and the biological behaviors were studied both in vivo and in vitro. By means of observation of histological sections and radioscopy, the biocompatibility of implant and their interface bonding mechanism with the surrounding tissues were evaluated.The results revealed that the impurity contents of C/C could meet the standard of artificial bone materials. What’s more, the 2400℃×2h graphitizing heat treatment could significantly reduce the main impurities in C/C and this material had similar microhardness to human bone. The mechanical properties testing results indicated that C/C have strain rate sensitivity and the reinforced fibers have remarkable effects in arresting propagating cracks and plasticizing. They could satisfy the mechanical demands of bone-repairing materials. The viscose based carbon/carbon composites have low friction coefficient. When they make up the friction pairs in vivo, the carbon particle desquamation might be less. The porous surface structure of scaffold material is beneficial to the direct adhesion, proliferation and differentiation of cells. The animal experiment of viscose based C/C applied in bone defection intramedullary fixation revealed that the bone defect areas were reconstructed by new bone trabecula. Immunohistochemical observations revealed that the implants had good tissue compatibility.The shear tests, phase composition analysis and fracture morphology observation results showed that the 700℃×10min post heat treatment could effectively increase crystallization and purity of the coatings. Through observation and analysis by electron microprobe and scanning electron microscopy, it is concluded that the bond strength of the plasma-sprayed HA coatings on C/C is mainly determined by the interface structure and can be further improved by the post heat treatment. Meanwhile, the implantation in vivo was carried out in hybrid goats. The histological observation revealed that the osteoplaque gradually grew on the surface of the HA coatings directly and the pure C/C surface was covered by the fibrous tissues. No inflammation symptoms were detected in the bone tissue around the implants. When as-sprayed HA coatings were immerged in simulated body fluid, it began to dissolute and the nuclearation as well as the growth of the new phases occurred. This process will provide an environment that is rich of Ca and P and benefit the osteoblast growth on the coatings.In the process of surface biomimetic activation treatment of C/C, concentrated nitric acid pre-oxidation treatment could change the few hydrogen bonds into oxygen-containing functional groups (such as hydroxyl group) on the surface of C/C. When the samples were immerged into the simulated body fluid at 37℃, hydroxyl group polycondensations occurred between the newborn in HA molecule and carbon/carbon composites. In this way, the high bonding strength of newborn HA and C/C was obtained by chemical bond bridging and the bioactivity of C/C was improved. At the same time, SiC modified film was prepared by Si reaction sintered on C/C. This film could lighten the carbon particle desquamation and be suitable as the protective and bonding film for biomedical C/C.Structure and property characterizations of the RF-PECVD prepared DLC film indicated that the type of carbon source gas is the key element to the quality of DLC film. With the deposition time prolonging, the particles that compose the film are growing up, surface roughness of the film is increasing. Under the condition that the flow ratio of CH4 and Ar is 1:20, the RF voltage is 17000V, the electric current is 0.45A and the diposition time lasts for 2h, the DLC film have high content of sp3 carbon atom, uniform thickness, good surface hydrophobic property and low surface friction coefficient. The study of DLC film prepared on the polished PAN based C/C revealed that there were two DLC Film-forming mechanisms. First, the non-homogeneous nucleation of DLC occurred on the pyrolytic carbon that composed C/C. Second, the homogeneous nucleation of DLC occurred in vacuum plasma environment. The surface morphology of C/C greatly influence to the microstructure of DLC film. Due to the dense structure of DLC film, it can be used as transition layer for the top bioactive layer on C/C.更多还原