Studies on Hepatocyte-Targeting Magnetic Resonance Imaging Macromolecular Contrast Media

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Electroosmotic Velocity in Fibrous Porous Media

A theory of electroosmosis in an array of parallel cylindrical fibers of Kozak and Davis (J. Colloid Interface Sci.,112, 403 (1986)), in which the liquid flow is normal to the axes of the cylinders, is developed to derive a simple approximate expression for the electroosmotic velocity for low zeta potentials without involving numerical integration. The relative error is less than 6%.     

多孔介质中甲烷水合物的生成特性的实验研究

在定容的条件下,实验研究了甲烷水合物在不同的多孔介质中的生成特性,所使用的多孔介质平均孔径为9.03,12.95,17.96与33.20 nm,其中孔径为12.95 nm的多孔介质使用了三个粒径范围,分别为0.105～0.150 mm,0.150～0.200 mm,0.300～0.450 mm;其他孔径的多孔介质的粒径...     

自组装多肽探针在磁共振成像中的应用

磁共振成像(MRI)是一种强大的非侵入式生物医学诊断技术. 临床上, MRI需要借助造影剂来提高成像质量, 从而提高诊断的准确性. 由于具有优越的信号放大能力和生物相容性, 自组装多肽探针可负载特定的MRI分子, 通过酶促自组装过程实现肿瘤靶向和特异性富集, 增强肿瘤病灶区MRI信号, 从而进一步提高MRI的准确性和灵敏度. 本综述总结了近年来多肽自组装探针在不同MRI模式( ¹H MRI, ¹⁹F MRI和双自旋核MRI)下的最新进展, 并展望了这类新型探针在MRI领域的应用前景.     

钾光卤石溶解动力学

研究了钾光卤石在不同分解液及不同温度的溶解机制，建立了溶解及结晶动力学方程     

Transport and Deposition of Alumina Nanoparticles in Water Saturated Porous Media: An Experimental Study

Transport and deposition of nanoparticles (NPs) have drawn great attention in different fields of engineering in recent years because of their potential risk to the environment. In this study, mobility of aluminum oxide NP, one of the most popular metal oxide NPs, was studied in synthetic saturated porous media. The impacts of ionic strength using monovalent (NaCl) and divalent (MgCl₂) salt solution, pH, and NPs concentrations on nano-alumina mobility were investigated. The experimental results showed that the transport of nano-alumina was influenced by ionic strength; the highest mobility was observed at the 0.01 M solution and decreased by increasing ionic strength. Moreover, the suspension containing alumina NPs presented the best mobility behavior in the acidic solution (pH = 2) in comparison with neutral and basic solutions. Consequently, transport of NPs with particle size distribution lower than 100 nm through porous media was facilitated at the acidic, low ionic strength condition. In addition, faster elution occurred when the influent concentration was increased from 0.1 wt% to 0.3 wt%. Finally, it is expected that ionic strength, pH of solution, and NPs concentration will be key parameters to control the nano-alumina mobility.     

氧化铁纳米颗粒在磁共振成像中的应用

目前临床诊断中钆基造影剂的应用十分广泛,然而其对人体的毒性无法忽视,因此研究者致力于低毒性造影剂的研发。氧化铁纳米颗粒(Iron Oxide Nanoparticles,IONP)因其超顺磁性在磁共振成像(Magnetic Resonance Imaging,MRI)中具有良好的暗对比效果,并且具有良好的生物相容性。随着生物材料和分子影像技术的发展,IONP在MRI成像中的应用愈发广泛。近年来,IONP在多模态成像和诊断治疗一体化方面取得了进展。本文将以IONP的MRI成像机理、制备和表面修饰为基础,阐述近年来IONP在MRI成像应用的研究成果和问题,期望IONP取得更好的发展。     

Flow Mechanism of Partially Cross-Linked Polyacrylamide in Porous Media

Partially cross-linked polyacrylamides (PCPAM) were prepared, and their rheological property, gel content, swelling property, and suspension property in saline solution were analyzed in laboratory. The goal of the research was to study the flow mechanism of PCPAM as a novel oil displacement agent in porous media. The migration behaviors of PCPAM were studied by single and series connection of double-tube sandpacked core flow experiments. The results showed that there was a critical pressure existing in the migration of PCPAM particles in porous media, and the migration was a dynamic process of plugging and flooding at the same time. When the pressure reached the critical pressure, the PCPAM particles would deform to pass through the pore throat and go ahead. Besides, the profile control experiments were conducted using a parallel connection of double-tube sandpacked core models, and the results revealed that PCPAM could generate “fluid diversion” and enlarge the swept volume of the lower permeable core. Moreover, micro-visualization displacement experiments were also carried out and proved that PCPAM could plug the high permeable pore throat to enlarge the swept volume, leading to an enhancement in oil recovery.     

磁共振成像造影剂的一些进展

本文综述了近年来磁共振成像造影剂的一些研究进展,对70余种钆配合物作了分类讨论。     

含钆温度敏感高分子核磁共振成像(MRI)造影剂的制备及研究

合成了一种新型可聚合型含钆单体,在温敏单体N-异丙基丙烯酰胺存在下,采用无皂乳液聚合法一步制备了含钆温度敏感的高分子微球.透射电子显微镜测试表明微球呈单分散性;动态光散射测试表明高分子微球的平均水合粒径约260 nm,呈现很窄的粒径分布;当温度从25℃升到45℃时,其粒径减小约60 nm,表明含钆高分子微球具有较好的温度敏感性.体外MRI测试表明,所得高分子微球的体外弛豫率为8.01(mmol/L)-1S-1(3 T),能有效的增强MRI信号,具有优良的MRI造影功能.上述结果表明,所得微球作为一种多功能MRI造影剂,在生物医学领域极具应用前景.     

Highly Loaded Semipermeable Nanocapsules for Magnetic Resonance Imaging

Magnetic resonance imaging has become an essential tool in medicine for the investigation of physiological processes. The key issues related to contrast agents, i.e., substances that are injected in the body for imaging, are the efficient enhancement of contrast, their low toxicity, and their defined biodistribution. Polyurea nanocapsules containing the gadolinium complex Gadobutrol as a contrast agent in high local concentration and high relaxivity up to 40 s⁻¹ mmol⁻¹ L are described. A high concentration of the contrast agent inside the nanocapsules can be ensured by increasing the crystallinity in the shell of the nanocapsules. Nanocapsules from aliphatic polyurea are found to display higher crystallinity and higher relaxivity at an initial Gadobutrol concentration of 0.1 m than aromatic polyurea nanocapsules. The nanocapsules and the contrast agent are clearly identified in cells. After injection, the nanocarriers containing the contrast agent are mostly found in the liver and in the spleen, which allow for a significant contrast enhancement in magnetic resonance imaging.     

利用两种模型预测多孔介质中气体水合物平衡分解条件

分别利用两种热力学方法(基于逸度相等的方法与基于活度相等的方法)预测了不同多孔介质中气体水合物的平衡分解条件, 对于非水合物相, 逸度方法采用Trebble-Bishnoi (TB)方程, 而活度方法则使用Soave-Redlich-Kwong (SRK)方程, 对于水合物相, 两种方法都利用了van der Waals-Platteeuw模型结合Llamedo等关于毛细管力作用模型来模拟. 两种方法的预测结果与实验结果吻合, 逸度方法的预测效果要好于活度方法.     

N-Aryl Amides as Chemical Exchange Saturation Transfer Magnetic Resonance Imaging Contrast Agents

Chemical exchange saturation transfer (CEST) MRI has recently emerged as a versatile molecular imaging approach in which diamagnetic compounds can be utilized to generate an MRI signal. To expand the scope of CEST MRI applications, herein, we systematically investigated the CEST properties of N-aryl amides with different N-aromatic substitution, revealing their chemical shifts (4.6–5.8 ppm) and exchange rates (up to thousands s⁻¹) are favorable to be used as CEST agents as compared to alkyl amides. As the first proof-of-concept study, we used CEST MRI to detect the enzymatic metabolism of the drug acebutolol directly by its intrinsic CEST signal without any chemical labeling. Our study implies that N-aryl amides may enable the label-free CEST MRI detection of the metabolism of many N-aryl amide-containing drugs and a variety of enzymes that act on N-aryl amides, greatly expanding the scope of CEST MR molecular imaging.     

Redox Properties and in Vivo Magnetic Resonance Imaging of Cyclodextrin-Polynitroxides Contrast Agents

This paper reports the synthesis, characterization and in vivo application of water-soluble supramolecular contrast agents (Mw: 5–5.6 kDa) for MRI obtained from β-cyclodextrin functionalized with different kinds of nitroxide radicals, both with piperidine structure ( CD2 and CD3 ) and with pyrrolidine structure ( CD4 and CD5 ). As to the stability of the radicals in presence of ascorbic acid, CD4 and CD5 have low second order kinetic constants (≤0.05 M⁻¹ s⁻¹) compared to CD2 (3.5 M⁻¹ s⁻¹) and CD3 (0.73 M⁻¹ s⁻¹). Relaxivity (r₁) measurements on compounds CD3 - CD5 were carried out at different magnetic field strength (0.7, 3, 7 and 9.4 T). At 0.7 T, r₁ values comprised between 1.5 mM⁻¹ s⁻¹ and 1.9 mM⁻¹ s⁻¹ were found while a significant reduction was observed at higher fields (r₁≈0.6-0.9 mM⁻¹ s⁻¹ at 9.4 T). Tests in vitro on HEK293 human embryonic kidney cells, L929 mouse fibroblasts and U87 glioblastoma cells indicated that all compounds were non-cytotoxic at concentrations below 1 μmol mL⁻¹. MRI in vivo was carried out at 9.4 T on glioma-bearing rats using the compounds CD3 - CD5 . The experiments showed a good lowering of T₁ relaxation in tumor with a retention of the contrast for at least 60 mins confirming improved stability also in vivo conditions.     

Prediction of Surfactant Retention in Porous Media: A Robust Modeling Approach

Demands for hydrocarbon production have been increasing in recent decades. As a tertiary production processes, chemical flooding is one of the effective technologies to increase oil recovery of hydrocarbon reservoirs. Retention of surfactants is one of the key parameters affecting the performance and economy of a chemical flooding process. The main parameters contribute to surfactant retention are mineralogy of rock, surfactant structure, pH, salinity, acidity of the oil, microemulsion viscosity, co-solvent concentration, and mobility. Despite various theoretical studies carried out so far, a comprehensive and reliable predictive model for surfactant retention is still found lacking. In this communication, a mathematical method based on machine learning approach, namely, least square support vector machine modeling is evolved for this purpose. To this end, the model was developed and tested using experimental dynamic surfactant retention data over a wide range of conditions. The results show that the developed model provides predictions in good agreement with experimental retention data. Moreover, it is shown that the developed model is capable of simulating the actual physical trend of surfactant retention versus three most important input parameters: total acid number of oil, pH, and mobility ratio. Finally, for detection of the probable doubtful retention data, outlier diagnosis was performed on the whole data set.     

Mathematical Model of Foam Flowing Characteristics by Snap-Off Mechanisms at Steady State in Porous Media

Flow characteristics and regeneration processes of foams were influenced by lamella properties and pore-throat structure in porous media. In this article, porous media was simplified as a bunch of constricted capillary tubes according to grain size, pore-throat radius, and immobile water saturation in porous media. Based on an analysis of forces upon liquid lamella, a mathematical model of foam migration and regeneration at steady state was established according to the mass conservation law and the momentum conservation law in porous media. The model could be used to calculate some important parameters in porous media, such as pressure distribution, shearing stress, lamella morphology, liquid-layer thickness, regeneration bubble size, etc. A series of flow experiments were carried out to investigate the influence of liquid properties and pore-throat structure on flow characteristics and resistance behavior of foams in porous media. The experimental results showed that pressure distribution monotonously decreased along porous media. The theoretical results were in good agreement with the experimental results. Foam structure, that is, foam quality was an important factor upon foam resistance behavior in porous media. The strongest resistance ability of foams was achieved at foam quality of 85% in porous media.      

15N Hyperpolarization of Dalfampridine at Natural Abundance for Magnetic Resonance Imaging

Signal Amplification by Reversible Exchange (SABRE) is a promising method for NMR signal enhancement and production of hyperpolarized molecules. As nuclear spin relaxation times of heteronuclei are usually much longer than those of protons, SABRE-based hyperpolarization of heteronuclei in molecules is highly important in the context of biomedical applications. In this work, we demonstrate that the SLIC-SABRE technique can be successfully used to hyperpolarize ¹⁵N nuclei in dalfampridine. The high polarization level of ca. 8 % achieved in this work made it possible to acquire ¹⁵N MR images at natural abundance of the ¹⁵N nuclei for the first time.     

超顺磁性Fe3O4纳米粒子在磁共振造影中的应用

超顺磁性Fe₃O₄纳米粒子由于其廉价、低毒及超顺磁等特性,已成为重要的一类磁共振造影剂.本文综述了超顺磁性Fe₃O₄纳米粒子的可控制备方法,归纳总结影响粒径、结晶度和磁性能的主要因素和影响规律;为进一步提高磁性能并实现多功能,总结了Fe₃O₄纳米粒子进一步组装和表面改性的方法和机理;系统讨论了Fe₃O₄纳米粒子的形貌、尺寸和表面性能等对磁性能和生物相容性的影响规律;并指出了Fe₃O₄纳米粒子在磁共振造影领域潜在的发展方向和研究热点.     

多孔介质中气体水合物降压分解的分形理论研究

通过将水合物的分解过程看作是无固态产物层生成的气固反应过程, 结合粒径缩小的收缩核反应模型和分形理论, 建立了多孔介质中水合物降压分解的分数维动力学模型, 提出了基于水合物分解实验数据计算多孔介质分形维数的方法. 分别利用前人的甲烷水合物和CO2水合物降压分解实验数据, 对上述分数维动力学模型进行了验证. 计算结果表明, 用提出的方法所计算得到的多孔介质分形维数与前人的测定结果基本符合; 对甲烷水合物和CO2水合物的降压分解过程, 提出的分数维动力学分解模型得出了和实验结果基本一致的预测, 绝对平均误差(AAD)小于10%.