【作者】 周智华；

【导师】 阮建明；

【作者基本信息】 中南大学 ， 生物材料学， 2007， 博士

【摘要】 聚-L-乳酸（PLLA）因其良好的生物相容性和可生物降解性,已应用于骨科替代材料等领域,但由于存在炎症反应和不具有生物活性、无骨传导能力等问题,限制了其进一步的应用。目前对PLLA材料的研究热点之一是通过与玻璃陶瓷复合,实现其生物降解可控性和生物活性的有机结合,应用于不同的植入环境。本文主要制备了具有超高分子量的聚-L-乳酸,通过采用纤维模压成型的方法获得了具有高强度的PLLA材料,并对PLLA等温结晶和非等温结晶进行了深入的理论研究。同时通过将PLLA和生物玻璃（BG）复合、成型,制备了具有生物活性和可降解性的复合材料,研究了生物玻璃改性与含量对复合材料力学性能的影响,并进一步研究了PLLA和PLLA/BG的体外降解行为。此外采用体外细胞培养和体内试验对PLLA/BG复合材料进行了生物学评介。首次合成了具有超高重均分子量的PLLA。以L-乳酸为原料制备L-丙交酯（LLA）,采用水洗-重结晶法纯化LLA,结果表明,采用水洗-重结晶法可得到高纯度的LLA,其收率达40.6%,比传统的重结晶法提高约12.1%。采用开环聚合法在140℃,单体与催化剂摩尔比（[M]/[I]）为12000,聚合时间为24小时的最佳工艺条件下制备的PLLA重均分子量达102.4×10⁴,分子量分布窄,其分布系数为1.16。改进传统溶液纺丝技术,首次提出了稀溶液沉析纺丝的新方法。采用稀溶液沉析纺丝方法制备了PLLA纤维,利用纤维取向模压技术制备了高强度的PLLA材料,并研究了成型工艺对材料力学性能的影响。研究结果表明,当PLLA溶液浓度为0.05g·mL^-1时,用稀溶液沉析纺丝可制得取向性能较好的具有多孔结构的PLLA纤维。将PLLA纤维在温度185℃,压力130MPa的条件下模压成型,材料的抗弯强度达238.8±6.5MPa,剪切强度达127.5±3.5MPa,其力学性能比传统成型方法大幅度提高。系统深入地研究了PLLA的等温和非等温结晶行为。非等温结晶结果表明,PLLA在低的降温速率(2℃·min^-1)下的结晶在118℃伴随有结晶区域的转变。玻璃化温度和结晶度随着降温速率的降低而增大。随着降温速率的降低,球晶尺寸增大,当降温速率大于10℃·min^-1时,PLLA接近为无定形材料。当PLLA在90℃-140℃等温结晶时,Avrami指数为n=3.01±0.13,表明PLLA以球晶方式生长。利用Hoffman-Lauritzen理论对PLLA的等温结晶机理进行了分析,研究表明结晶RegimeⅡ和RegimeⅢ的转变温度为118℃左右,成核常数Kg（Ⅱ）和Kg（Ⅲ）分别为6.025×10⁵K²和1.307×10⁶K²,且Kg（Ⅲ）/Kg（Ⅱ）为2.17,接近2,与LH理论一致。采用溶胶—凝胶法制备了CaO-SiO₂-P₂O₅生物玻璃,并进行了体外活性实验（invitro）。生物玻璃具有典型的介孔结构,介孔分布较窄,孔径小于10 nm。经模拟体液（SBF）浸泡后,在生物玻璃表面有一层碳酸羟基磷灰石颗粒（0.5-10μm）生成,表现出优异的生物活性。采用蒸发溶剂的方法制备了PLLA/BG薄膜,并采用模压成型的方法首次制备了PLLA/BG复合生物材料,通过控制生物玻璃的含量实现对PLLA/BG复合材料初始强度的调控。同时对PLLA/BG薄膜进行了体外生物活性研究;以3-氨丙基-三甲氧基硅烷（APS）作为偶联剂,对生物玻璃进行了表面改性,并考察了APS改性和生物玻璃含量对复合材料力学性能的影响。研究结果表明,PLLA/BG薄膜在SBF中浸泡3天后在表面生成了碳酸羟基磷灰石的棒状晶体,具有择优生长现象,14天后,在复合材料的表面同时有棒状晶体和HCA层生成,表现出较好的生物活性。生物玻璃表面经APS处理后,颗粒分散均匀,同时改善了其在PLLA基质中的分散性,提高了复合材料的力学强度,生物玻璃含量为10wt%时,PLLA/BG材料的抗弯强度达153.9±8.8MPa。PLLA/BG复合材料的抗弯强度和剪切强度随生物玻璃含量的增大而下降,但其抗弯模量随之而升高。随着生物玻璃含量的增加,PLLA/BG材料逐步具有典型脆性断裂的特征。系统研究了PLLA和PLLA/BG材料在PBS中的降解行为,并首次得出了PLLA/BG降解的动力学方程。结果表明,PLLA和PLLA/BG材料的吸水率、失重率随降解的进行逐渐增加,而PBS溶液的pH值、材料的力学性能和相对分子量则呈降低趋势,分子量分布逐渐变宽,但PLLA/BG复合材料比PLLA变化较慢。PLLA的熔融温度、熔化焓和结晶度随降解的进行都呈现出先升高后降低的趋势。PLLA的降解属于本体水解,呈“双态降解”规律。生物玻璃的存在并未改变PLLA的降解机理,但减缓了酸对PLLA的催化降解作用。两种材料的降解均符合一级反应动力学,37℃时,PLLA和PLLA/BG在PBS中的降解速率常数分别为9.2×10^-3day^-1和6.4×10^-3day^-1。采用体外细胞试验和体内试验对PLLA/BG复合材料进行了细胞毒性和生物相容性评介,同时考察了PLLA/BG复合材料与组织界面的成骨能力,并成功地进行了兔子股骨髁间骨折试验。结果表明,PLLA/BG复合材料无急性毒性,无致热原,不导致溶血,无遗传毒性,无抑菌作用,无非感染性炎症;该复合材料有良好的组织相容性,并具有较好的成骨能力;兔子股骨髁间骨折试验表明复合材料其强度以及降解特性可以维持兔股骨髁间骨折固定的初始稳定性,8周后骨折基本愈合,是一种具有发展前途的骨折内固定材料。更多还原

【Abstract】 Poly-L-lactide （PLLA） with the merits of good biocompatibility and biodegradability has been applied to bone replacement materials. A major drawback of PLLA, once implanted, however, is the release of acidic degradation products which may lead to inflammatory responses. Another limitation is its lack of bioactivity, which means, for the case of bone tissue engineering, that it do not allow bone apposition or bonding on the polymer surface. Composite materials, based on PLLA and ceramic, with bioactivity and different biodegradation rate have attached a lot of attention in the biomaterials field and become a hot research topic.In this paper, poly-L-lactide with ultra-high weight average molecular mass was synthesized, and PLLA materials were fabricated by fiber oriented moulding, moreover, non-isothermal and isothermal melt crystallization of PLLA were investigated. PLLA/BG composite was obtained by mouding, the effects of modification and content of bioactive glass on the properties of PLLA/BG were investigated, and the degradation behaviors of PLLA and PLLA/BG in vitro were also studied. Besides, the toxicity and biocompatibility of PLLA/BG have been evaluated in vitro and in vivo.Poly-L-lactide with ultra-high weight average molecular mass was synthesized for the first time by ring-opening polymerization from high purity L-lactide. Combinations of watering and two times’ recrystallization can improve the purity and the yield of L-lactide. The yield of L-lactide reachs 40.6% and increases 12.1% compared with the simplex recrystallization method. Poly-L-lactide with a weight average molecular mass of about 102.4×10⁴ and polydispersity index of 1.16 was obtained when polymerization was conducted with molar ratio of monomer to initiator （[M]/[I]） 12000 for 24 h at 140℃.A new technique of diluted solution extracting and spinning was presented for the first time to obtain PLLA fiber. PLLA materials were fabricated by fiber oriented moulding and the effects of molding pressure and temperature on the mechanical strength of PLLA were also investigated. The good oriented fiber with porous structure （0.1～1μm） was obtained by diluted solution extracting and spinning method. Bending and shearing strength of the samples increase firstly and then decrease with the increase of molding temperature and pressure. The bending and shearing strength are 238.8±6.5MPa and 127.5±3.5MPa, respectively, on conditions that molding temperature is 185℃and the pressure is 130MPa, which are enhanced more than traditional moulding methods.The influence of non-isothermal melt crystallization on thermal behavior and isothermal melt crystallization kinetics of PLLA were investigated. Crystallization performed at lower cooling rates (2℃·min^-1) is accompanied by a variation of the kinetics around 118℃. The glass transition temperature of PLLA decreases with increase of cooling rate, and the crystallinity at the end of crystallization increases with decreasing cooling rate. The size of PLLA spherulites increases with a decrease in the cooling rate, and PLLA becomes almost amorphous cooled at rapid rate (>10℃·min^-1). PLLA exhibits an Avrami crystallization exponent n = 3.01±0.13 in isothermal crystallization in the range from 90℃to 140℃. According to Hoffman-Lauritzen theory, two crystallization regime are identified with a transition temperature occurring at 118℃, and the value of Kg（III）/Kg（II） is 2.17 [K_g（II）=6.025×10⁵K², K_g（III）=1.307×10⁶K²].The bioactive glass of CaO-SiO₂-P₂O₅ was prepared by using the sol-gel method, and the bioactivity in vitro was investigated after soaking in the simulated body fluid （SBF） at 37℃. Bioactive glass is typical amorphous material with mesopore diameters varied from 1 to 10μm. After 7 days in SBF, the surfaces consisted of spheres with diameters ranging between 0.5μm to 10μm, which composed of needle-like crystallites with crystallinity similar to that of a biological apatite.PLLA/BG film was fabricated by a solvent evaporation technique and PLLA/BG composite materials were obtained for the first time by mouding method. The bioactivity of PLLA/BG film in vitro was also studied. The bioactive glass was modified by 3 -aminopropyltrimethoxysilane （APS）, and the effects of APS modification and bioactive glass content on mechanical properties were also investigated. Rod-like HCA crystals deposited on the surface of PLLA/BG film after soaked in SBF for 3 days. Both rod-like crystals and HCA layer formed on the surface after 14 day in SBF. The high bioactivity of PLLA/BG composite indicates the potential of materials for integration with bone. Glass particles treated by APS are better incorporated into polymer-rich phase during the phase separation process. Therefore, an improved interface between PLLA and bioactive glass particles is formed with the coverage of PLLA on glass particles, and the mechanical properties were enhanced. Bending strength reaches 153.9±8.8MPa when the content of bioactive glass is 10 wt%. With the increasing of the amount of bioactive glass, the bending strength of composite decreases while the bending modulus increases. The shearing strength also decreases as the amount of bioactive glass increases. A typical morphology of brittle failure with a smooth fracture surface is observed with increasing bioactive glass content.The degradation behaviors of PLLA and PLLA/BG composite in PBS solution were investigated in detail, and the kinetics of PLLA/BG was obtained for the first time. The results indicate that mass loss, water uptake and polydispersity index of PLLA and PLLA/BG increase with the increasing time, however, pH value, mechanical strength and weight average molecular mass decrease. The melting temperature, melting enthalpy and crystallinity of PLLA firstly increase, and then decrease as the increasing degradation time. The degradation kinetics of PLLA and PLLA/BG composite are indicative of an autocatalysis process and simple bulk hydrolysis, and presented the modal of "biomodal degradation". The speed of degradation of PLLA/BG is slowed down by incorporating bioactive glass. The degradation behaviors of both PLLA and PLLA/BG comply with first-order kinetics, and the rate constants of the biodegradation process of PLLA and PLLA/BG are 9.2×10^-3day^-1 and 6.4×10^-3day^-1, respectively. The probability of PLLA/BG composite for internal fixation of bone fracture was expounded and proved from the point of the initial strength, the retention of strength and the modulus of the composite.The toxicity and biocompatibility of PLLA/BG composite materials were evaluated in vitro and in vivo, and the bone-bonding ability of PLLA/BG composite was also carried out. The rabbits with malleolar fracture were treated successfully by interal fixation using screws made of PLLA/BG composite. PLLA/BG composite has no acute toxicity, hemolysis, pyrogen characteristic, bacteria-restraining and nonbacterial inflammatory. The results of biocompatibility test show that the bioactive glass existing in the PLLA composite facilitates both adhesion and proliferation of rat fibroblast on the PLLA/BG composite film and extracting solution. A good ability of bone-bonding of PLLA/BG was deterinined by implantation into rabbit muscle. Malleolar fracture of rabbits was healed in 8 weeks in the main, which indicates that PLLA/BG has a great prospect for fixation of bone fracture.更多还原