刺激响应型树状分子凝胶的研究进展※

近年来, 刺激响应型超分子凝胶作为一类智能软物质材料, 在离子识别材料、自修复材料、生物材料和药物缓释等领域展现出了非常好的应用前景, 受到人们广泛关注. 树状分子是一类具有高度支化结构的大分子, 其形成的凝胶兼具有机小分子凝胶和聚合物凝胶的双重优点, 树状分子丰富的多层次支化几何结构有利于修饰不同功能基团, 从而确保各功能基团彼此独立作用而不相互干扰, 这种特性使其在构筑多功能化凝胶材料, 尤其是多重环境刺激响应型凝胶材料方面具有独特优势. 基于此, 本综述从树状分子凝胶因子设计、成凝胶机理、响应性能和响应机理等方面详细归纳了刺激响应型树状分子凝胶的研究进展. 按照刺激源不同, 主要从光响应型、氧化还原响应型、离子响应型、触变响应型和多重响应型五个方面对刺激响应树状分子凝胶进行了系统归纳总结. 最后, 基于目前刺激响应树状分子凝胶存在的一些问题对该领域未来发展进行了展望.     

超分子凝胶可视化选择性识别有机小分子的研究进展

近年来,超分子凝胶作为一类非常重要的软物质材料而受到广泛关注,当前研究面临的最大问题之一是智能响应性,而智能响应性凝胶材料发展的一个重要研究方向是可视化选择性识别有机小分子。本文从有机小分子的类型(手性分子、位置异构体和氨基酸等)出发,较系统地综述了可视化选择性识别有机小分子的超分子凝胶的研究进展情况,并对该研究领域作了简单展望。     

环境响应的智能小分子有机凝胶材料

小分子有机凝胶(low molecule organogel,LMOG)是近年来逐渐发展起来的一类新型自组装材料,随着研究的深入,LMOG的功能化特别是对环境有智能响应的凝胶体系引起人们极大的研究兴趣.本文综述了4类智能响应的凝胶体系的研究进展,即:光响应小分子凝胶体系,主要是凝胶因子内含有偶氮苯、二芳乙烯等光致变色基...     

基于胆固醇的有机超分子智能凝胶

胆固醇分子具有特色的多环、多手性碳结构,因此可用于构筑有机超分子凝胶智能材料。该凝胶体系除了对温度有良好的感知响应性外,对其他的外界刺激,如光、pH、超声等也能够感知并响应。由于胆固醇分子是生命体中普遍存在的生物分子,基于胆固醇的有机超分子智能凝胶在生命现象模拟、药物输运等方面具有天然的优势。本文先根据胆固醇凝胶体系的不同种类,包括光响应型、氧化还原响应型、酸碱响应型、超声响应型,金属离子响应型以及触变响应型等,对该体系的结构与性能进行了介绍,然后介绍了对凝胶因子的修饰方法,最后结合目前的研究现状,探讨了胆固醇有机超分子凝胶的应用方向及前景。     

智能响应型水凝胶药物控释体系及其应用

药物控释体系可改善药物分子在机体内的释放、吸收、代谢和排泄过程,显著提高药物利用率并减弱药物的毒副作用。智能响应型水凝胶凭借其刺激响应性、亲水性和无毒性在药物控释方面得到了广泛的关注。本文介绍了智能响应型水凝胶药物控释体系的概念、机理和应用,详细归纳了智能响应型水凝胶药物控释体系的研究进展。按照刺激源不同将智能响应型水凝胶药物控释体系分为pH响应型、温度响应型、光响应型、生物分子(如葡萄糖、酶)响应型、外场(如电场、磁场)响应型、压力响应型、氧化还原响应型及多重响应型水凝胶药物控释体系。进一步介绍了智能响应型水凝胶药物控释体系在治疗癌症、急性肾损伤、眼病、糖尿病等疾病及抗菌、防止伤口感染等方面的应用。最后,基于目前智能响应型水凝胶药物控释体系存在的一些问题(如生物相容性差、存在突释或滞释现象、不可降解等)对其发展做出了展望。     

刺激响应型石墨烯材料的研究新进展

石墨烯是一种具有六角型蜂巢状晶格的二维碳纳米材料,它由碳原子以sp2电子轨道杂化形成,它的高比表面积以及优良的力学、电学、光学和热学性能使它成为智能材料的基本构筑单元。利用具备特定功能的聚合物、小分子或者纳米粒子对石墨烯进行修饰或者杂化,得到具备相应刺激响应性能的石墨烯材料,与传统的刺激响应型高分子材料相比,它具备更佳的力学性能以及更好的环境稳定性,有望在致动器、传感器、自愈合材料、光热治疗以及可控药物输送等方面得到应用。本文简要概述了近年来利用对温度、pH、电、光以及有机分子等刺激响应的聚合物和小分子化合物对石墨烯进行修饰,并赋予其智能响应特性的方法以及相关应用研究,分析了现有智能响应石墨烯材料的不足,展望了其未来的应用前景以及发展方向。     

刺激响应降解型聚合物水凝胶

作为一类重要的高分子材料,聚合物水凝胶由于其优良的理化性能和生物学特性而被广泛应用于生物医药领域,降解特性是其作为生物医用材料的重要性能指标。刺激响应降解型水凝胶是指在环境因素刺激下凝胶网络发生响应性断裂,进而产生凝胶-溶胶或溶胀-降解转变的一类智能高分子材料。这一响应降解特性可通过将环境敏感性断裂基团引入到聚合物凝胶网络中来实现。与水凝胶常规的水解、酶解相比,刺激响应降解因具有空间或时间上的可控特性而引起人们的广泛关注。本文重点介绍了p H响应、光响应以及氧化还原响应降解型聚合物水凝胶的设计方法、降解机理及其最新研究进展,并对刺激响应降解型水凝胶未来的研究方向进行了展望。     

基于β-环糊精的有机小分子凝胶

环糊精是直链淀粉在环糊精葡萄糖基转移酶作用下生成的含有7个D-吡喃葡萄糖单元的环状低聚糖,具有斜截锥形空间立体结构,腔内疏水,腔外亲水。β-环糊精以其低廉的价格、良好的水溶性和生物相容性,在超分子化学领域得到广泛的应用。β-环糊精可用于凝胶的构筑,通常的方法是将β-环糊精接枝到高分子链上,再以得到的高分子链为凝胶因子构筑高分子凝胶。虽然基于β-环糊精的高分子凝胶得到了广泛的关注和研究,但是,直接以β-环糊精为凝胶因子构筑的有机小分子凝胶却鲜有报道。2010年,本课题组首次报道了一种基于β-环糊精和二苯胺的热致有机凝胶。此后,本课题组在β-环糊精有机小分子凝胶领域做了大量的研究工作。本文在实验室研究工作的基础上,首先介绍了β-环糊精有机小分子凝胶的分类和不同因素对凝胶形成的影响,然后深入探讨了β-环糊精有机小分子凝胶的形成机理,系统介绍了β-环糊精有机小分子凝胶的刺激响应性以及在药物载运领域的应用,最后,对β-环糊精有机小分子凝胶的发展前景进行了展望。     

智能纳米水凝胶的刺激响应性研究进展

智能纳米水凝胶在药物输送与可控释放、医学诊断、生物传感器、微反应器、催化剂载体等方面有良好的应用前景。结合本课题组近年来的研究成果,分别介绍了具有温度刺激响应性、pH刺激响应性、光刺激响应性、磁场刺激响应性、分子识别刺激响应性和多重刺激响应性智能纳米水凝胶的研究进展。另外,对这几种智能纳米水凝胶目前存在的问题和今后的发展方向提出了一些粗浅的看法。     

刺激响应型超分子凝胶

随着超分子化学的日益发展,刺激响应型超分子凝胶作为一种超分子材料受到人们广泛关注。超分子凝胶是由非共价键作用力自组装而成,基于这一特性,当超分子凝胶受到外界刺激(如温度、光、pH、化学物质、机械力等)时,该凝胶能够产生响应,如溶胶-凝胶转化、颜色变化或荧光变化等。刺激响应型超分子凝胶在离子识别材料、自修复材料、生物材料等领域展现出了非常好的应用前景。本文综述了近五年来刺激响应型超分子凝胶的研究进展,并根据刺激种类的不同,将超分子凝胶分为以下几类:热敏感型超分子凝胶、化学物质和pH响应型超分子凝胶、光敏感型超分子凝胶、氧化还原响应型超分子凝胶、机械力刺激响应型超分子凝胶和多重刺激响应型超分子凝胶。本文根据上述分类对超分子凝胶进行了介绍,同时对该研究领域作了展望。     

Electro-responsive polyacrylamide-grafted-gum ghatti copolymer for transdermal drug delivery application

An application of polyacrylamide-grafted-gum ghatti (PAAm-g-GGH) copolymer for transdermal delivery of an anti-psychotic drug, quetiapine fumerate triggered by electric stimulus was explored. The electro-responsive PAAm-g-GGH was prepared by free radical polymerization underneath nitrogen atmosphere subsequent to alkaline hydrolysis. The PAAm-g-GGH was used as drug reservoir gel and crosslinked films of GGH and PVA as rate controlling membranes (RCM). The reservoir gels were uniform and translucent; pH of gels was 6.56–7.06, which is in the pH range of skin and drug content was from 89.57% to 94.51%. The thickness of RCMs was 163–227?μ; thickness was increased with increased glutaraldehyde concentration and all the RCMs were permeable to water vapors. When electric stimulus was absent, a small amount of drug was permeated from the formulations, while drug conveyance was enhanced in the existence of stimulus. Drug permeation was increased with increase in electric stimulus from 2 to 8?mA. Over two fold increase in flux was observed after application of electric stimulus. Under “on–off” electric stimulus, faster drug permeation was seen under ‘on’ condition and permeation was decreased when stimulus was ‘off.’ Histopathology study confirmed reversible alteration of skin structure under electric stimulus.     

Liquid-crystalline physical gels

Liquid-crystalline (LC) physical gels are a new class of dynamically functional materials consisting of liquid crystals and fibrous aggregates of molecules that are called "gelators". Liquid-crystalline physical gels, which are macroscopically soft solids, exhibit induced or enhanced electro-optical, photochemical, electronic properties due to the combination of two components that form phase-separated structures. In this tutorial review, we describe the materials design and structure-property relationships of the LC physical gels. The introduction of self-assembled fibers into nematic liquid crystals leads to faster responses in twisted nematic (TN) mode and high contrast switching in light scattering mode. Furthermore, the LC physical gels can be exploited as a new type of materials for electro-optical memory. This function is achieved by the control of reversible aggregation processes of gelators under electric fields in nematic liquid crystals. Electronic properties such as hole mobilities are improved by the introduction of fibrous aggregates into triphenylene-based columnar liquid crystals. The incorporation of photochromic azobenzenes or electroactive tetrathiafulvalenes into the chemical structures of gelators leads to the preparation of ordered functional materials.     

Well-defined liquid crystal gels from telechelic polymers

Well-defined liquid crystal networks with controlled molecular weight between cross-links and cross-link functionality were prepared by "click" cross-linking of telechelic polymers produced by ring-opening metathesis polymerization (ROMP). The networks readily swell in a small molecule liquid crystal, 5CB, to form LC gels with high swelling ratios. These gels exhibit fast, reversible, and low-threshold optic switching under applied electric fields when they are unconstrained between electrodes. For a given electric field, the LC gels prepared from shorter telechelic polymers showed a reduced degree of switching than their counterparts made from longer polymer strands. The reported approach provides control over important parameters for LC networks, such as the length of the network strands between cross-links, cross-linker functionality, and mesogen density. Therefore, it allows a detailed study of relationships between molecular structure and macroscopic properties of these scientifically and technologically interesting networks.     

Switchable friction of stimulus-responsive hydrogels

Poly(N-isopropylacrylamide) (pNIPAAm) gels are stimulus-responsive hydrogels that exhibit large reversible changes in their volume and surface physicochemical properties near the lower critical solution temperature (LCST) in response to external stimuli, such as a change in temperature or solvent composition. Here we report how different phase states, induced isothermally by changes in the solvent composition, affect the tribological properties of pNIPAAm hydrogels. Our measurements indicate that gels in a collapsed conformation (above the LCST) exhibit significantly more friction than swollen gels (below the LCST) at low shear rates. These differences arise from changes in the surface roughness, adhesive interactions, and chain entanglements of the gel surfaces associated with the phase transition. Importantly, we show that the changes in friction, triggered by an external stimulus, are reversible. These reversible and possibly tunable changes in friction may have a significant impact on the design of coatings for biosensors and for actuation devices based on stimulus-responsive hydrogels.     

Insulator-metal transitions induced by electric field and photoirradiation in organic Mott insulator deuterated κ-(BEDT-TTF)2Cu[N(CN)2]Br

The Mott insulator-metal transition induced by an external stimulus such as electric field, pressure, chemical doping, or photoirradiation has received considerable attention because of the potential use in new optoelectronic functional devices. Here we report an abrupt Mott insulator-metal transition observed as a current jump in a molecular-based Mott insulator, namely, deuterated κ-(BEDT-TTF)(2)Cu[N(CN)(2)]Br, where BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene, upon application of a pulsed voltage of certain magnitude (threshold voltage). Furthermore, the threshold voltage needed for the transition is shown to be reduced by photoirradiation. Thus, the Mott insulator-metal transition can be controlled by a combination of an external electric field and photoirradiation.     

pH-敏感的疏水型凝胶在直流电场中的刺激响应

合成了不同疏水链长的甲基丙烯酸酯、甲基丙烯酰胺及丙烯酸与 4 ,4′ 二 (甲基丙烯酰胺基 )偶氮苯交联共聚的聚电解质凝胶 .该凝胶在非接触电场中发生消溶胀 ,但疏水侧链较长的凝胶在发生消溶胀之前经历了一个溶胀过程 .凝胶在电场中首先弯向阴极 ,随着时间的延长或电压的升高弯向阴极 ;并出现弯曲的方向或弯曲的程度的波动 .当撤去电场后 ,凝胶又能恢复到初始的形态 .凝胶的这些性质既与电渗、电扩散及电解有关 ,亦与凝胶的疏水相互作用有关     

Synthesis and characterization of a hydrogel with controllable electroosmosis: a potential brain tissue surrogate for electrokinetic transport

Electroosmosis is the bulk fluid flow initiated by application of an electric field to an electrolyte solution in contact with immobile objects with a nonzero ζ-potential such as the surface of a porous medium. Electroosmosis may be used to assist analytical separations. Several gel-based systems with varying electroosmotic mobilities have been made in this context. A method was recently developed to determine the ζ-potential of organotypic hippocampal slice cultures (OHSC) as a representative model for normal brain tissue. The ζ-potential of the tissue is significant. However, determining the role of the ζ-potential in solute transport in tissue in an electric field is difficult because the tissue's ζ-potential cannot be altered. We hypothesized that mass transport properties, namely the ζ-potential and tortuosity, could be modulated by controlling the composition of a set of hydrogels. Thus, poly(acrylamide-co-acrylic acid) gels were prepared with three compositions (by monomer weight percent): acrylamide/acrylic acid 100/0, 90/10, and 75/25. The ζ-potentials of these gels at pH 7.4 are distinctly different, and in fact vary approximately linearly with the weight percent of acrylic acid. We discovered that the 25% acrylic acid gel is a respectable model for brain tissue, as its ζ-potential is comparable to the OHSC. This series of gels permits the experimental determination of the importance of electrokinetic properties in a particular experiment or protocol. Additionally, tortuosities were measured electrokinetically and by evaluating diffusion coefficients. Hydrogels with well-defined ζ-potential and tortuosity may find utility in biomaterials and analytical separations, and as a surrogate model for OHSC and living biological tissues.     

Effects of pulse strength and pulse duration on in vitro DNA electromobility

Interstitial transport of DNA is a rate-limiting step in electric field-mediated gene delivery in vivo. Interstitial transport of macromolecules, such as plasmid DNA, over a distance of several cell layers, is inefficient due to small diffusion coefficient and inadequate convection. Therefore, we explored electric field as a novel driving force for interstitial transport of plasmid DNA. In this study, agarose gels were used to mimic the interstitium in tissues as they had been well characterized and could be prepared reproducibly. We measured the electrophoretic movements of fluorescently labeled plasmid DNA in agarose gels with three different concentrations (1.0%, 2.0% and 3.0%) subjected to electric pulses at three different field strengths (100, 200 and 400 V/cm) and four different pulse durations (10, 50, 75, 99 ms). We observed that: (1) shorter pulses (10 ms) were not as efficient as longer pulses in facilitating plasmid transport through agarose gels; (2) plasmid electromobility reached a plateau at longer pulse durations; and (3) plasmid electromobility increased with applied electric energy, up to a threshold, in all three gels. These data suggested that both pulse strength and duration needed to be adequately high for efficient plasmid transport through extracellular matrix. We also found that electric field was better than concentration gradient of DNA as a driving force for interstitial transport of plasmid DNA.     

Switchable mirrors of chiral liquid crystal gels

Chiral nematic liquid crystal compositions containing mono- and di-acrylates in mixtures with non-reactive liquid crystal molecules were produced. Defect-free planar macroscopic alignment of the molecules was induced between uniaxially rubbed substrates. Polymerization of the acrylate groups was initiated photochemically leading to the formation of a new class of chiral gels consisting of a lightly cross-linked network containing non-reactive molecules. In this way, the chiral pitch and, hence, the reflection colour became permanently fixed. Under the influence of an electric field the gels could be switched to the homeotropic state and reverted to the planar defect-free state upon removal of the electric field. Depending on the composition of the gel, either the position of the reflection band remained the same while its magnitude and/or width decreased, or its position shifted to smaller wavelengths with increasing electric field. Some of the gels showed sharp switching characteristics with a hysteresis making them suitable for passive matrix addressing with a high degree of multiplexability. The gels also showed fast switching times as they reverted to the defect-free optical state upon removal of the electric field. The phase structure of the gels was studied using dielectric spectroscopy which showed that the gels have an inhomogeneous structure.     

The electric field dependence of DNA mobilities in agarose gels: a reinvestigation

The electric field dependence of the electrophoretic mobility of linear DNA fragments in agarose gels was reinvestigated in order to correct the observed mobilities for the different temperatures actually present in the gel during electrophoresis in different electric field gradients. When corrected to a common temperature, the electrophoretic mobilities of DNA fragments less than or equal to 1 kilobase pairs (kbp) in size were independent of electric field strength at all field strengths from 0.6 to 4.6 V/cm if the gels contained less than or equal to 1.4% agarose. The mobilities of larger DNA fragments increased approximately linearly with electric field strength. If the agarose concentration was higher than 2%, the mobilities of all DNA fragments increased with increasing electric field strength. The electric field dependence of the mobility was larger in gels cast and run in Tris-borate buffer (TBE) than in gels cast and run in Tris-acetate buffer (TAE), and was more pronounced in gels without ethidium bromide incorporated in the matrix. Ferguson plots were constructed for the various DNA fragments, both with and without extrapolating the temperature-corrected mobilities to zero electric field strength. Linear Ferguson plots were obtained for all fragments less than or equal to 12 kbp in size in agarose gels less than or equal to 1.4% in concentration if the mobilities were first extrapolated to zero electric field strength. Concave upward curvature of the Ferguson plots was observed for DNA fragments greater than or equal to 2 kbp in size at finite electric field strengths. Convex downward curvature of the Ferguson plots was observed for DNA fragments greater than or equal to 1 kbp in size in agarose gels greater than or equal to 2% in concentration. The mobilities of the various DNA fragments, extrapolated to zero agarose concentration and zero electric field strength, decreased with increasing DNA molecular weight; extrapolating to zero molecular weight gave an "intrinsic" DNA mobility of 2.7 x 10(-4) cm2/Vs at 20 degrees C. The pore sizes of LE agarose gels cast and run in TAE and TBE buffers were estimated from the mobility of the DNA fragments.(ABSTRACT TRUNCATED AT 400 WORDS)