【作者】 王佃刚；

【导师】 陈传忠；

【作者基本信息】 山东大学 ， 材料学， 2009， 博士

【摘要】 羟基磷灰石（Hydroxyapatite,HA）因其具有良好的生物相容性和生物活性,并且存在于动物的骨和牙等硬组织中,已成为临床医学上应用比较广泛的种植体材料。但是块状HA强度低、脆性大,不能应用于人体的承载部位。为了改善种植体的机械性能,可将HA作为薄膜材料沉积到金属基体如钛及其合金表面来获得机械性能和生物性能都优异的种植体。目前HA薄膜的制备方法有等离子喷涂、溶胶-凝胶、磁控溅射、电泳沉积等方法,这些传统方法在HA薄膜的制备方面都取得了一定的成功,但所制备的薄膜存在HA分解、非晶化严重、与基体结合强度低等缺点。上世纪80年代发展起来的脉冲激光沉积技术（Pulsed Laser deposition,PLD）因其能够制备化学成分计量比准确、与基体结合强度高的薄膜,在薄膜制备中逐渐显示出其优势,也为HA生物薄膜的制备提供了一项新技术。另外,HA与钛合金在热膨胀系数等机械性能上差别较大,种植体在环境温度发生变化时会导致种植体表面裂纹的产生,影响种植体的使用寿命。因此可以将生物活性更高、热膨胀系数低但溶解速度快的45S5玻璃与HA混合,制备HA/45S5复合薄膜,不但可以提高薄膜的结合强度,而且有利于薄膜生物活性的增加。本文采用脉冲激光沉积技术在钛合金Ti-6Al-4V表面制备HA/45S5复合生物薄膜,综合利用扫描电镜（SEM）、电子探针（EPMA）、X-射线衍射（XRD）、傅立叶转换红外光谱（FTIR）、原子力显微镜（AFM）等测试方法对沉积的薄膜的微观组织结构进行表征,通过体外模拟体液浸泡试验研究薄膜的生物活性,并对薄膜的生物安全性进行评价。试验结果表明,脉冲激光沉积HA/45S5复合薄膜的表面存在大量的直径为0.2～3μm的球形和不规则形状的颗粒。靶材中原有45S5成分在沉积后仍旧以非晶的形式存在,HA则会部分发生分解生成β-Ca₃（PO₄）₃,其结晶度受到沉积工艺条件的影响很大。薄膜沉积后HA晶格中的羟基丢失,Si-O-Si四面体网络结构发生畸变,导致Si-O键的振动吸收峰向低值偏移,并产生Si-O非桥氧键（Si-O-NBO）。脉冲沉积工艺对薄膜的组织结构、相组成、薄膜的结合强度等影响很大。衬底温度的升高为等离子体在基体表面的沉积注入了新的能量,有利于更多的粒子在表面沉积,导致薄膜表面颗粒数目增多,粗糙度增加,同时有利于提高薄膜的结晶度以及薄膜与基体的结合强度。衬底温度的升高还加速P的丢失,使薄膜中的Ca/P原子比增大。反应气氛压力的减小意味着反应室中气体分子密度的降低,等离子羽辉中粒子与气体分子碰撞的几率降低,能量损失减少,沉积到基体表面的粒子所具有的动能更大,与基体的结合强度更高。但气氛压力减小会使等离子羽辉的锥角变大,P更容易丢失,薄膜粗糙度和结晶度都随之降低。微氧气氛可促使低熔点的P氧化,在薄膜冷却过程中减少P元素的丢失,降低薄膜的Ca/P原子比,并且存在CO₃^2-离子替代OH^-离子的现象。另外,薄膜形成的初始阶段,沉积的粒子沿着基体表面外延生长,与基体间存在很好的晶格匹配,因此激光脉冲数目越少,薄膜与基体的结合力越大。靶材成分不同对薄膜的表面形貌影响不大,主要影响薄膜中P、Na元素的丢失程度,靶材中45S5的相对含量越高,薄膜的P、Na元素丢失越严重。45S5玻璃的添加会引起薄膜结晶度的降低,同时会影响HA的晶格取向,当45S5添加量为20 wt.%和50 wt.%时,薄膜中HA发生c轴择优取向。HA晶体结构中OH^-具有严格的[0001]取向,激光烧蚀过程中OH^-极易失去,形成了c轴取向的空穴通道。薄膜形成过程中,在外来粒子的作用下,磷灰石晶体便有可能沿着[0001]方向生长形成c轴取向。45S5的添加会降低薄膜与基体间热膨胀系数的差异,有利于提高薄膜与基体的结合强度,但过高的45S5添加量又会导致薄膜非晶化严重,使结合强度降低。本试验中,当45S5的添加量为20 wt.%时,薄膜结合强度最大,临界载荷为18.7N。45Pa氩气气氛下,衬底温度为200℃时50 wt.%HA+50 wt.%45S5薄膜为非晶态,适当热处理可有效提高薄膜的结晶度以及与基体的结合力。600℃热处理1h后薄膜的临界载荷为17.5N,但随着温度的提高和保温时间的延长,热处理又会破坏薄膜的完整性,使薄膜与基体的结合强度呈下降趋势。热处理温度一定时,随着保温时间的延长,薄膜晶粒尺寸逐渐增大。保温时间为2h时,700℃热处理的薄膜中的HA呈现a轴取向,薄膜表面析出细小的颗粒物,800℃热处理的薄膜的HA则呈现c轴取向,薄膜表面析出针状组织。热处理温度的提高和保温时间的延长会使Si-O四面体网状结构中由外来粒子引起的晶格畸变程度降低,导致FTIR结果中Si-O单非桥氧功能团吸收峰强度减弱甚至消失,同时使739cm^-1附近的Si-O弯曲振动吸收峰向高值区偏移。体外模拟体液浸泡试验表明生物薄膜在模拟体液浸泡过程中的初始阶段溶解行为占主导地位,而后以沉淀行为为主,所制备的HA/45S5薄膜具有良好的生物活性,但薄膜的溶解和沉淀速率受到结晶度的影响。含有45S5成分的薄膜在浸泡过程中,薄膜中的Na⁺、Ca²⁺等离子会迅速与体液中的H⁺或者H₃O⁺发生离子交换,P元素则以PO₄^3-、HPO₄^2-、H₂PO₄^-等形式快速溶于体液中,而薄膜中的Si-O-Si键遭到破坏后Si元素以Si（OH）₄的形式溶解于体液中。体液中Si（OH）₄在薄膜表面附近浓度很大,极易发生缩聚反应形成[SiO₂]聚合体,并在薄膜表面沉积后形成多孔网状结构的富Si凝胶层,加上Zeta电势的作用,当薄膜表面附近体液中Ca²⁺、PO₄^3-离子浓度达到饱和时,Ca²⁺、PO₄^3-离子的扩散会在凝胶层上形成非晶CaO-P₂O₅,非晶CaO-P₂O₅与OH^-、CO₃^2-等离子结合后便结晶形成羟基磷灰石或者碳酸磷灰石。HA薄膜在模拟体液浸泡时,新钙磷层的形成过程主要受Zeta电势的影响。当薄膜表面附近的溶液中Ca²⁺、PO₄^3-离子达到饱和时,Ca²⁺、PO₄^3-离子便会交替在薄膜表面沉积形成新的钙磷层。薄膜在模拟体液浸泡后的FTIR结果表明溶解过程中原始薄膜的基团的吸收峰强度逐渐减弱甚至消失,随后新沉积的磷灰石的基团的吸收峰出现并不断增强。在沉积过程中,磷灰石结构中容易形成CO₃^2-离子的B型替代形成碳酸磷灰石。XRD结果表明随着浸泡时间的延长,非晶薄膜逐渐有HA析出,结晶度逐渐升高,而结晶度较高的HA薄膜和衬底温度为600℃时50 wt.%HA+50 wt.%45S5薄膜浸泡后其结晶度经历先降低后增高的过程。通过溶血试验、L929细胞毒性作用试验和急性全身毒性试验对所制备的薄膜进行了生物安全性评价。结果表明,本试验中所制备的薄膜无细胞毒性作用,不会引起溶血反应和急性全身毒性反应,对细胞生长和增殖无抑制现象,对试验动物没有产生毒害作用,具有良好的生物相容性,符合生物安全性要求。更多还原

【Abstract】 Hydroxyapatite (HA, Ca₁₀（PO₄）₆（OH）₂) which has the similar chemical composition and structure to the nature Ca phosphate mineral present in a biological hard tissue, is one of the most attractive materials for human hard tissure implant due to its excellent biocompatibility and bioactivity properties. However, the brittle nature of HA ceramic limits its clinical use in a load-bearing situation. It is the only advantage if it is used as a film material based on a metal substrate such as titanium and its alloy, and this kind of implants combines the mechanical benefits of metal alloy with the biocompatibility of bioceramic. Nowadays, HA films have been widely studied by many methods including plasma spraying, sol-gel, magnetron sputterin, electrophoretic deposition and so on, and a certain successful application has been obtained by these traditional methods especially by plasma spraying. However, there are many drawbacks of the films produced by these methods: decomposition of HA, low crystallinity, poor mechanical bonding between the film and the substrate. Pulsed laser deposition （PLD） offers a new technique for preparing HA film because PLD can deposite the films which have good mechanical bonding and similar stoichiometry of the target. In addition, the difference of the coefficient of thermal expansion between HA and Ti alloy induces the formation of cracks which decreases the service life of the implant. One of the solution way is to mixture HA with 45S4 bioglass which has better bioactivity, low coefficient of thermal expansion and rapid dissolution rate in simulated body fluid （SBF）, and this kind of HA/45S5 composite films would have higher bioactivity and bonding strength between film and substate. In this paper, HA/45S5 composite films were deposited by PLD on Ti-6A1-4V, the microstructure, phase constitution, functional groups characteristic and bonding strength of the deposited films were investigated by scanning electron microscopy （SEM）, X-ray diffraction （XRD）, electron probe microanalysis （EPMA）, Fourier transform infrared spectroscopy （FTIR）, atomic force microscopy （AFM） and so on, the bioactivity was studied by immersion in SBF, and biological safety was evaluated by hemolysis test, in vitro cytotoxicity test and acute systemic toxicity test.The experimental results show that there are many global and irregular particles with a diameter of 0.2-3μm on the PLD HA/45S5 composite film surface. The compositions in 45S5 remain amorphous state after deposition, part of HA decomosite intoβ-Ca₃（PO₄）₃ and the crystallinity is influenced the deposited parameters greatly. Hydroxyl groups in HA crystal lose, and the tetrahedron network structure of Si-O-Si is rearranged which results in the shift of peak position of Si-O vibration towards lower values in infrared absorbance spectra, simultaneously non-bridging silicon-oxygen （Si-O-NBO） bonds form.There are great influences of deposition parameters on the microstructure, phase constitution, bonding strength of the HA/45S5 composite films. High substrate temperature can compensate for the energy loss of vaporized species and contribute to deposition process of more species on the substrate surface, consequently the particles density and the surface roughness increases. High substrate temperature also increases the crystallinity of the film which is helpful for the increase of the bonding strength between film and substrate. However, high substrate temperature accelerates the loss of P element, thus increases the Ca/P atomic ratio of the film.The reduction of the atmosphere pressure means the decrease of the gas molecule density in the reaction chamber, which induces the decrease of the collision probability between the species in plumes and gas molecule, hence decrease the energy loss. So the species which reach the substrate surface have more kinetic energy, consequently the bonding strength between film and substrate increases. With the decrease of the atmosphere pressure, the surface roughness and the crystalinity of the film increase, and the cone angle become larger which diminish the restraint for the species and accelerate the P loss. In micro-oxygen atmosphere, the P element with low melting point is easily oxidized, and the P loss can be decreased during cooling processing which can decrease the Ca/P ratio. What’s more, phenomenon of the CO₃^2- substitution for PO₄^3- was observed. The first deposited species, which have the epitaxial growth characteristic along the substrate surface, have good lattice matching with the substrate, so the bonding strength increases with the pulses number decreasing.The target composition has little influence on the surface morphology, but has great influence on the P and Na loss degree. Generally, the higher the relative content of 45S5 in target material is, the more serious P and Ca lose. The addition of 45S5 decreases the crystallinity of the whole film and affects the crystal orientation of HA. When the additive quantity of 45S5 is 20 wt.% or 50 wt.%, c-axis preferred orientation occurs. As we all know, the OH^- has the strict [0001] orientation in HA crystal, and OH^- easily loses during PLD process which induces the formation of cavity channel with the [0001] direction. During the film forming process, apatite maybe grows along the [0001] direction to form c-axis orientation with the action of foreign particles. The addition of 45S5 also can decrease the difference of the coefficient of thermal expansion between HA and Ti alloy which is helpful to enhance the bonding strength between the film and the substrate. However, excessively high addition quantity of 45S5 enhances the non-crystallization trend of the film, consequently decrease the bonding strength. In this experiment, when the addition quantity of 45S5 is 20 wt.%, the bond strength reaches maximum value, and the critical load is 18.7N.50 wt.% HA+50 wt.% 45S5 film deposited with a substrate of 200℃at 45 Pa Ar atmosphere is amorphous, and proper post-heat treatment can increase the crystallinity and the bond strength of the film. The critical load of the film treated at 600℃for 1h is 17.5N, and with the increase of temperature and prolongation of holding time, the integrality of the film is destroyed by the heat treatment, thus the bond strength has the downward trend. When temperature remains constant, the crystal grows up with the prolongation of time. When the holding time is 2h, the film treated at 700℃has the characteristics of a-axis preferred orientation, and fine granular particles precipitate, while the film treated at 800℃has the characteristics of c-axis preferred orientation, and acicular structure was observed in the surface. With the increase of temperature and prolongation of holding time, the degree of lattice distortion of the tetrahedron network structure of Si-O-Si induced by the foreign particles decreases, which weakens the absorption intensity and even eliminates its existence of Si-O-NBO bonds. Furthermore, the bend vibration absorption peak of Si-O at 739 cm^-1 shifts towards high values in infrared absorbance spectra.The in vitro immersion tests indicate that the PLD composite films have good bioactivity, and the dissolution and reprecipitation rate are influenced by the film crystallinity. After immersion in SBF, the dissolution behavior of the PLD films will dominate at the beginning and then reprecipitation behavior dominates.During the immersion process of the films contained 45S5 composition, ions exchange occurs immediately between the Na⁺, Ca²⁺ ions in film and the H⁺ or H₃O⁺ in solution, P element dissolves into the solution by the forms of PO₄^3-, HPO₄^2-, H₂PO₄^-, and Si element dissolves by the forms of Si（OH）₄ after Si-O-Si bonds are destroyed. When the concentration of Si（OH）₄ near the film surface is saturated, [SiO₂] polymer easily forms after condensation reaction, and the [SiO₂] polymer can precipitate on the film surface to form a SiO₂-rich layer which has a porous network structure. With the action of zeta potential, Ca²⁺ and PO₄^3- ions will reprecipitate onto the SiO₂-rich layer to form amorphous CaO-P₂O₅ layer. After incorporation of OH^-, CO₃^2- from solution, crystallization of amorphous CaO-P₂O₅ leads to the formation of HA or carbonated apatite. For HA film, after the dissolution of Ca²⁺, PO₄^3- ions into solution, the reprecipitate process is mainly controlled by the zeta potential. Once the Ca²⁺, PO₄^3- ions in the solution near the film surface is saturated, they will reprecipitate onto the film surface alternatively to form new CaP film.After immersion in SBF, the FTIR results show that the characteristic absorption peak intensity of the as-deposited films decreases gradually and even vanishes, afterward the characteristic absorption peak of newly formed apatite appears and then enhances. By the way, carbonated apatite easily forms by B-type substitution of CO₃^2- ion. The XRD results show that with the prolongation of the immersion time, the crystallinity of the amorphous films increase gradually, while for the films with high crystallinity, the crystallinity decreases first and decreases afterward.The biological safety of PLD films was evaluated by hemolysis test, in vitro cytotoxicity test and acute systemic toxicity test. The results indicate that the films deposited in our experiments have no hemolysis action, no cytotoxicity and no acute systemic toxicity. No obvious inhibitive effect was observed on the growth and proliferation of L929 cells, and no poisoning effect was observed on the tested animals, which means the PLD films deposited in our experiments have good biocompatibility and exhibite good biological safety for clinical trial.更多还原