【作者】 兀晓文；

【导师】 侯万国；

【作者基本信息】 山东大学 ， 胶体与界面化学， 2014， 博士

【摘要】 层状双金属氢氧化物(Layered Double Hydroxides,简称LDHs),又称为类水滑石(Hydrotalcite-like compounds,简称HTlc),是由两种或两种以上金属元素组成的具有水滑石层状结构的氢氧化物,层板由于同晶取代而荷结构正电荷,层间存在可交换的阴离子,近期在药物载体中的应用受到广泛关注。药物分子可插入LDHs层间形成纳米杂化物,由于药物分子与层板间的相互作用及空间位阻效应而具有良好的药物缓释效果,被认为是极具应用前景的药物缓释新剂型。药物插层LDHs(简记为药物-LDHs)纳米杂化物的制备已有很多研究报道,常用的方法有离子交换、共沉淀和结构重建等,但这些方法多适合于阴离子型水溶性药物,而对非离子型(或电中性)疏水性(水难溶性)药物难以实现有效负载,因缺乏插层驱动力。为此,提出了二次插层法(secondary intercalation method)和药物修饰-离子交换法等,可实现疏水性药物的插层负载,但载药量低。近期,很多文献报道了LDHs的剥离-重组装(Delamination-reassembly)研究。在一定条件下,LDHs颗粒可剥离成单元晶片或纳米片(nanosheets),与有机物重组装可恢复层状结构而形成有机-LDHs纳米杂化物,并已成功用于有机-LDHs超薄膜和高分子-LDHs纳米杂化物的制备,过程简易、条件温和,但用于药物-LDHs纳米杂化物的制备还未见报道。因此,探索剥离-重组装法制备药物-LDHs纳米杂化物的可行性及特点,对LDHs基药物靶向控释剂型的研发具有重要意义。另外,通常制备的药物-LDHs纳米杂化物分散性差、聚集严重,限制其实际临床应用。如何有效地改善药物-LDHs纳米杂化物的分散稳定性,是一个亟待解决的问题。脂质体(或囊泡)是由磷脂分子的闭合双分子层包裹水相核所形成的一种有序分子组合体,用作药物载体的研究已有大量文献报道。我们设想,脂质体也可作为修饰体,用于包覆修饰药物-LDHs纳米杂化物形成复合体,可简记为(药物-LDHs)@脂质体复合体,预期脂质体膜的空间保护作用能有效改善纳米杂化物的分散稳定性；加之脂质体本身就具有良好的生物相容性,且易于靶向修饰,因此有望构筑成一类新型的药物靶向控释体系,是一个值得探索研究的课题。喜树碱(Capmtothecin, CPT)是一种已应用于临床治疗的抗肿瘤药物,也是相关研究中常采用的非离子型疏水性药物模型,抗癌活性强,但毒副作用大,且有效期短,实际临床效果并不理想,研制靶向缓释剂型对其临床应用具有重要意义。本文以CPT为非离子型疏水性药物模型,探索研究了剥离-重组装法制备CPT-LDHs纳米杂化物,脂质体包覆修饰纳米杂化物制备(CPT-LDHs)@脂质体复合体,并对其载药量、晶体结构、形貌等进行了表征,考察了药物释放行为和分散稳定性等性能,以期为LDHs基药物缓释剂型的研制提供依据。本文的主要研究内容和结论：(1)研究了剥离-重组装法制备脱氧胆酸根(deoxycholate, DC)-LDHs纳米杂化物,并对其进行了表征；考察了制备条件对晶体结构和DC负载量的影响,探索了DC在层间的分布状态。其目的一是考察剥离-重组装法的可行性和特点,二是构建一个可负载非离子型疏水性药物的通用平台(或复合物体系)。结果表明,剥离-重组装是制备LDHs纳米杂化物的有效途径,且过程简单,条件温和(常温),通过改变原料比例即可方便地调控晶体结构和客体负载量。(2)研究了剥离-重组装法制备CPT-LDHs纳米杂化物,并对其进行了表征。首先,用生物相容性的表面活性剂(surfactant, Sur)胆酸钠(sodium cholate, Ch)或脱氧胆酸钠(sodium deoxycholate, DC)包覆CPT形成载药胶束,再与LDHs剥离纳米片共组装,形成CPT-Sur-LDHs纳米杂化物。考察了制备条件对载药量的影响以及药物释放行为,探讨了CPT及表面活性剂阴离子(Ch或DC)在LDHs层问的分布状态。结果表明,所采用的剥离-重组装法可实现CPT的高效负载,载药量可达13.5%；Ch或DC在LDHs层间呈双层排列,CPT插于其中；纳米杂化物具有明显的药物缓释效果,释放过程复合Bhaskar方程和Parabolic扩散模型,颗粒内部扩散为释放过程的速控步骤。(3)以蛋黄卵磷脂为主要成膜物质,逆向蒸发法形成脂质体,对脂质体包覆修饰CPT-LDHs纳米杂化物进行了研究,考察了所形成(CPT-LDHs)@脂质体复合体的形貌、分散稳定性、再分散性以及药物释放行为等。结果表明,复合体具有良好的分散稳定性和再分散性,证明脂质体包覆修饰是解决药物-LDHs纳米杂化物分散性差的有效途径；另外,与CPT-LDHs纳米杂化物相比,复合体表现出更好的药物缓释性能,表明是具有发展潜力的新型药物控释体系。(4)研究了CPT-氧化石墨烯(graphene oxide, GO)-LDHs纳米杂化物的共组装法制备,以探索新型载药体系。现将CPT负载于GO单层片表面,再与LDHs纳米片共组装,形成CPT-GO-LDHs纳米杂化物,考察了纳米杂化物的载药量和药物释放行为。结果表明,CPT-GO-LDHs纳米杂化物载药量明显低于CPT-Sur-LDHs纳米杂化物,仅为13.4mg/g(或1.34%),但具有良好的缓释效果,有何有效提高载药量是一个有待研究的问题。更多还原

【Abstract】 Layered double hydroxides (LDHs), also called anionic clays or hydrotalcite-like compounds, are an important class of layered inorganic materials. The brucite-like LDH layers possess structural positive charges due to the isomorphous substitution, which are counterbalanced by interlayer hydrated anions. LDHs are widely studied as drug delivery system. The drug can be intercalated into the gallery of LDHs to form the drug-LDH nanohybrids, which are considered as potential drug delivery and controlled-release system because of the host-guest interaction and steric-hinerance effect.There have been many reports on the synthesis of drug-LDH nanohybrids, mainly including co-precipitation, ion exchange, reconstruction and hydrothermal methods. Nevertheless, these conventional methods are most suitable for the intercalation of anionic water-soluble drugs. It is difficult for the water-insoluble or neutral charge drugs to be intercalated into the interlayer of LDHs due to the lack of driving force. Thus, the secondary intercalation or drug-modification ion exchange methods were raised to prepare the water-insoluble drug intercalated LDH nanohybrids. Recently, the delamination of LDHs attracts much attention because the nanosheets can be used as positive charged building block to prepare nanohybrid materials. And the delamination-reassembly is widely studied to synthesis organic-LDH ultrathin film and macromolecule-LDH nanohybrids thanks to their facile process and mild conditions. But to the best of our knowledge, the delamination/reassembling process has not been reported to prepare the drug-LDHs nanohybrids. Therefore, it is important to explore the feasibility and characteristics of delamination/reassembling method to synthesis the drug-LDHs nanohybrids for the targeted drug delivery-controlled release systems.In addition, the clinical application is limited for the poor water dispersion and serious aggregation. In order to solve these problems, liposome has been introduced into related study. Liposome is an artificially prepared spherical vesicle composed of a lipid bilayer with an aqueous interior, which is widely studied as drug delivery system. Herein, we make an assumption that liposome is used as a modification material for the coating of drug-LDH nanohybrids to improve the water dispersion of nanohybrids owing to steric-hinerance effect. Accordingly, the drug-LDHs@liposome nanocomposites have the potential to be a new targeted drug controlled-release system for the biocompatibility and surface modification.Camptothecin (CPT) is a kind of efficient clinical anticancer drug. But its application has been limited by the poor solubility, toxicity, side effect and short effective reaction time. So it is of great importance to develop the new delivery system for improving the solubility, stability and controlling the release of CPT.In this work, we take the water-insoluble and charge-neutral anticancer drug, CPT, as model drug to explore the preparation of CPT-LDH nanohybrids via delamination-reassembling method. The CPT-LDH@liposome nanocomposites were also synthesized by reverse evaporation method. In order to reach better understanding of drug-LDHs system, the drug loading amounts, crystal structure, morphology of CPT-LDH nanohybrids and CPT-LDH@liposome nanocomposites were characterized by XRD, TEM, UV-vis, Zeta potential, particle size and so on. Besides, the drug release and dispersibility were studied as well.Main contents and conclusions:(1) We chose the biocompatible surfactant deoxycholate as the guest molecule and Mg3Al-NO3LDH as the host material to synthesis DC-LDH nanohybrids via the delamination/reassembling method. The so-synthesized nanohybrids were characterized by XRD, TEM, FT-IR, elemental analyses and TG-DSC. The DC anions arrange as a slight tilted bilayer with the long axis perpendicular to the brucite-like layer. The feasibility and characteristic of delamination/reassembling method were investigated. It was proved that this strategy exhibited the advantages of short reaction time and mild experimental conditions and the loading amount of DC in the nanohybrids could be easily controlled by changing the ratio of DC to LDH. What’s more, a new system was built for the encapsulation of water-insoluble drugs.(2) We chose the water insoluble anticancer drug, CPT, as the guest molecule and Mg3Al-NO3LDH as the host material to synthesis CPT-LDH nanohybrids via the delamination/reassembling method. The so-synthesized nanohybrids were characterized by XRD, TEM, FT-IR, elemental analyses and UV-vis. For this route, CPT molecules were initially incorporated into the micelles of a biocompatible surfactant, such as sodium cholate (SCh) or sodium deoxycholate (SDC). The resulting negatively charged CPT-loaded micelles and the positively charged LDH nanosheets were then co-assembled together to form CPT-Sur-LDH nanohybrids. It revealed that the loading of CPT in the nanohybrids could reach as high as13.5%, indicating that this route could be used to achieve the effective intercalation of charge-neutral and poorly water-soluble drugs into the LDH gallery. The in vitro release of CPT from the nanohybrids had been examined, and the results showed that the release was a diffusion-controlled process and that the diffusion process through the LDH particles was the rate-limiting step. The parabolic diffusion equation effectively described the kinetic process associated with the release of CPT from the nanohybrids.(3) The nanocomposites of liposome coated CPT-LDHs were synthesized by the optimized reverse evaporation method. The morphology, mean diameter, stability, and redispersion were characterized. CPT-LDHs were successfully encapsulated in the aqueous interior of liposome. It indicated that the CPT-LDH@liposome nanocomposites have good dispersion stability and re-dispersibility in water. The coating of liposome outside the CPT-LDH nanohybrids is an effective method to solve the problem of poor dispersion stability. The in vitro release profiles of CPT from the nanocomposites were examined, indicating that the nanocomposite is a novel pH-responsive drug delivery system and the diffusion through the particles the rate limiting step.(4) Ananohybrid of CPT-graphene oxide (GO)-LDHs is synthesized by using the delamination-coassembling method. For the coassembly route, CPT molecules were initially loaded on the surface of GO nanosheets; the resulting negatively charged CPT-loaded GO nanosheets and the positively charged LDH nanosheets were then coassembled together into the layered CPT-GO-LDH nanohybrid, in which the GO nanosheets and the LDH nanosheets were alternatively stacked and the CPT molecules were located in its interlay er gallery. The so-obtained nanohybrid was characterized by XRD、TEM、FT-IR、UV-vis and TGA/DSC. The drug loading amount, only13.4mg/g (1.34%), is lower than the CPT-Sur-LDH nanohybrids, which would be addressed in the future work.更多还原