【作者】 郑晓彤；

【导师】 周绍兵；

【作者基本信息】 西南交通大学 ， 材料学， 2009， 博士

【摘要】 本论文主要以生物降解高分子聚-D,L-乳酸（PDLLA）为基质,复合生物活性无机粒子,如羟基磷灰石（HA）、β-磷酸三钙（β-TCP）和四氧化三铁（Fe₃O₄）等,制备具有热致型形状记忆特性的可生物降解复合材料;并探讨复合材料的形状记忆效应的机理,材料降解过程的机理,以及聚合物与无机相之间的界面作用机理;期望得到一种安全、有效且具有形状记忆功能的可生物降解高分子复合材料,为生物材料在此相关领域的进一步拓展提供一个理论支持。首先,我们在论文第二章研究了具有可生物降解、生物相容性和形状记忆特性的PDLLA和HA复合材料。通过动态力学性能分析（DMA）,我们可发现:PDLLA/HA复合材料的储能模量（E’）在T_g前后具有明显差异,与玻璃态相比橡胶态的E’降低最多的达到两个数量级。这个结果证明了PDLLA/HA复合材料可能具有形状记忆效应。我们进一步通过形象的形状记忆回复实验说明这种效应,同时系统地考察了相关的形状记忆性能参数。实验结果显示,PDLLA/HA复合材料在一定的复合比例范围内有非常好的形状记忆效应,其形状回复率可达95%以上。生物活性HA粒子的加入也可提高PDLLA高分子材料的形状记忆效应。在论文第三章我们进一步研究了PDLLA与纳米HA复合后能产生形状记忆效应的机理。因此,在本章中,我们从聚合物的分子链与无机相的界面作用机理分析入手,揭示出两相之间可能存在氢键作用力。纳米复合材料通过溶液混合和热压复合成一种高分子为基体的热致型形状记忆材料,然后通过傅立叶变换红外光谱仪（FTIR）和X-射线光电子能谱仪（XPS）的检测分析,得出PDLLA中的羰基（C=O）和HA中的表面羟基（P-OH）有可能产生了氢键连接。基于实验数据,我们解释复合材料为什么有好的行状记忆特性;并构建了具有形状记忆性的复合模型,较形象地描绘了该复合材料产生形状记忆性能的原因。为了进一步验证我们对PDLLA/纳米HA复合材料的形状记忆效应机理的分析,我们在论文第四章还尝试利用Materials Studio（MS）软件来模拟、计算PDLLA和纳米HA的界面作用机理,从理论上与前面的实验结果进行对比、分析。得到的计算机模拟结果证实纳米复合材料中两相之间确实存在一定的键能作用;这就比较符合我们实验检测的PDLLA和HA两相之间的界面作用关系和形状记忆效应的结果。既然界面关系可以直接影响到复合材料的形状记忆性能,那么为了得到界面结合更好的有机与无机复合材料,我们在论文第五章通过原位合成的方法制备了明胶（Gel）/PDLLA/HA纳米复合材料。HA晶体在聚合物基质中形核、矿化,最终长成一种纤维状的无机纳米晶体。表征结果显示:矿化的HA晶体与聚合物的Gel和PDLLA分子链存在离子相互作用,并在两种聚合物之间起到“桥梁”作用,形成了一种复杂的网络结构,这也有助于复合材料产生更好的记忆效应。另外,明胶既作为一种复合成分,又作为一种改性剂,对HA纳米纤维的矿化、生长和复合材料的合成也起到一种有利的作用。研究具有形状记忆功能的可生物降解高分子复合材料最终目的是应用于人体,因此,我们认为探讨降解过程对材料形状记忆行为的影响非常必要。在论文第六章,我们系统地研究了PDLLA/β-TCP复合材料的体外降解性能,以及与记忆性能的关系。PDLLA与β-TCP的复合材料经过56天的体外降解,材料的重量、分子量、降解介质pH值、有机与无机界面都发生了改变,这也直接导致材料的形状回复率降低。但并不是随时间的增加一直变差,在降解21到28天之间时,其形状回复率略有反弹。通过XRD、IR等分析推测,聚合物分子量的波动和无机物发生一定的相转变使得复合材料的形状记忆性能也发生了非线型的变化。最后,我们探讨了具有磁性的可生物降解复合材料在交变磁场的条件下通过诱导纳米磁性粒子发热引起的形状记忆效应。首先,通过聚乙二醇（PEG）改性,化学共沉淀方法制备出20nm左右的Fe₃O₄磁性粒子,再与PDLLA复合。形状记忆性能测试是在超音频交变磁场环境下感应加热,我们观察到复合材料产生了形状记忆行为,并对产生这些现象的原因进行了初步分析。更多还原

【Abstract】 In this dissertation,the thermo-induced shape memory and biodegradable composites consisted of poly（D,L-lactide）（PDLLA） as polymeric matrix and inorganic particles such as hydroxyapatite（HA）,β-tricalcium phosphate（β-TCP） and magnetic iron oxide（Fe₃O₄） were prepared.Moreover,mechanism of shape memory effect,biodegradation and interface action of composites was also analyzed and discussed.The aim of these studies was that the safe and effective composites possessing shape memory effect and biodegradation are designed and a theoretical support for biomedical application can be provided.Firstly,PDLLA/HA composites were studied,which possess biodegradation, biocompatibility and shape memory properties.We could find the result by dynamic mechanical analysis（DMA） that storage modulus at the rubbery state is about two orders of magnitude larger than that at the glassy state,which could indicated that PDLLA/HA composites had desirable shape memory effect.It could also be identified by the shape memory testing and the parameters of shape memory properties.As a result,the shape recovery ratios（Rs） of the PDLLA/HA composites were above 95%.The results could conclude that bioactive HA particles in composites played an important role during the shape memory recovery.So,it was very significant for investigation of the mechanism that the composites of amorphous PDLLA and HA nanoparticles could show well shape memory effect.Based on the analysis of interface action between the molecular segments of polymer and inorganic phase,we revealed the existence of hydrogen bonding in nanocomposites.The PDLLA/HA nanocomposites were prepared by solution mixture and thermal mold-pressure.The results of Fourier transform infrared spectroscopy（FT-IR） and X-ray photoelectron spectroscopy（XPS） indicated that the hydrogen bonding between the C=O in PDLLA and the surface P-OH groups of HA nano-crystalline was formed indeed.The improvement of shape memory properties further implied the existence of hydrogen bonding in nanocomposites.Moreover,a schematic model of the hydrogen bonding was designed on the base of the experimental results,which could clearly explain the memory mechanism of nanocomposites.In addition,the interface action of PDLLA and nano-HA was simulated and computed by Materials Studio（MS） software,so that could compare with previous experiment results.The results of MS simulation could clearly indicate that some interaction between polymer and inorganic phase existed in nanocomposites,which were in agreement with the examined results of experiment.In order to obtain polymer/inorganic composite with well interface,a novel biodegradable polymer-ceramic nanocomposite was prepared by the in-situ biomimetic method,which consisted of Gelatin（Gel）,PDLLA and HA nanofibers. The results of XRD and IR showed that the HA nanofibers played an important role on the existence of bridging bond between polymeric Gel and PDLLA in the nanocomposite.The schematic model of two polymeric chains bridged by inorganic nanofibers was designed on the base of the experimental results,which could well show the interaction mechanism of three phases and explain the mechanism of improvement of the shape memory effect.Moreover,the Gel could initiate and regulate the mineral growth of HA crystals along the functional groups of molecular chains of polymer.It was also very signifcant for the investigation on effect of in vitro degradation of PDLLA/β-TCP composites on theirs shape memory properties.Thus, we prepared PDLLA/β-TCP composites with different weight ratios.The shape-memory behaviors of composites during degradation process of 56 days were performed.During degradation,the dispersed morphology,T_g,molecular weight, weight loss and pH change of composites were all changed,which could result in the decrease of reovery ratios of composites.The reaction formulae of crystalline phase transformation could explain that the change of shape memory properties of PDLLA/β-TCP composites might result from the new inorganic particles in degradation.Finally,the biocompatible PDLLA/Fe₃O₄ nanocomposites were prepared and their magnetic-field induced shape memory effect was also investigated.The Fe₃O₄ nanoparticles with an average size of 20 nm were synthesized by chemical co-precipitation method with the modifying of polyethylene glycol（PEG）.Moreover, the magnetic-field induced shape memory effect of composites was performed in an alternating magnetic field.As a consequence,PDLLA/Fe₃O₄ nanocomposites displayed excellent shape memory effect.Moreover,the reason of the phenomenon was also further analysed.更多还原