Belousov-Zhabotinsky反应驱动的智能高分子材料:拓扑结构及仿生功能

化学自振荡反应驱动的智能高分子材料常被称为自振荡高分子材料(self-oscillating polymer materials, SOPMs),其中以Belousov-Zhabotinsky(BZ)反应驱动的SOPMs研究最为深入,为高分子材料领域的一大研究热点。与传统智能高分子材料不同,SOPMs体系具有高度的自调节性,即可以不需要外界“开-关”转换的刺激就能自动、可逆、周期性地发生状态转变。本文结合SOPMs的最新研究结果,介绍该类材料在新型拓扑结构设计和仿生功能研究两个方面的新思想和新方法。在拓扑结构设计方面,主要介绍梳形自振荡高分子凝胶、“聚轮烷”互锁自振荡高分子凝胶、多级结构自振荡高分子凝胶、超级交联自振荡高分子凝胶、支化自振荡高分子、自振荡高分子刷以及嵌段自振荡高分子材料。在仿生功能研究方面,主要阐述自振荡高分子囊泡、人工细胞、自主肠状运动、趋光避光运动。最后,对SOPMs今后的发展作了展望。     

基于Belousov-Zhabotinsky自振荡反应的智能高分子

自振荡高分子是基于Belousov-Zhabotinsky自振荡反应(BZ反应)设计的一类新型智能高分子,其物理、化学性质可以在相对封闭且无外界刺激的BZ反应溶液中发生自主、可逆和循环的变化。本文从概念、设计原理、设计方法及潜在应用4个方面系统介绍了自振荡高分子,其中重点结合自振荡高分子的化学结构设计与物理结构设计介绍了这一领域的研究进展:详细归纳了目前已成功制备的具有不同化学结构或物理结构的自振荡高分子或凝胶,阐述了不同的设计方法的优点、存在的问题及可能的解决办法,最后介绍了自振荡高分子在自动运输智能表面、凝胶机器人、自主转动马达等方面的设计实例,并分析了该领域面临的问题及今后发展趋势。     

光响应性微凝胶的分子设计和智能材料构筑

微凝胶能够在外界刺激下改变自身尺寸,是一类重要的智能材料构筑基元。光刺激具有可远程控制、能快速切换等特点,在刺激响应性材料的设计中受到了广泛关注。将光刺激响应性基元引入到微凝胶体系,可以得到一系列具有重要应用前景的智能材料。本文综述了近年来光响应微凝胶的研究进展,总结了赋予微凝胶光响应性的四种分子设计,包括光致异构化型、光致生热型、光致(解)交联型、光致生酸型;介绍了光响应微凝胶在调光材料、药物控释、信息显示和自修复凝胶等领域的应用;展望了该领域的研究方向、发展和应用前景。     

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。     

自振荡凝胶的仿生运动

定向运动是生命体最基本的功能,是其进化、生存和繁衍的前提。近年来为了研究生命体的运动机制,许多人工系统被相继开发并用于模拟部分生命体的运动行为。在诸多人工仿生系统里,自振荡凝胶由于同时具有内部驱动产生动能、运动定向性、无缆化和环境自适应等性能而备受瞩目。本文介绍了自振荡凝胶仿生运动的化学-机械能转换的理论根源并综述了仿生运动模式研究近期的进展,在此基础上展望了自振荡凝胶运动研究面临的机遇、挑战和未来发展方向。     

化学振荡反应调控的动态可逆智能体系

动态可逆作用是构筑智能材料体系,实现材料性能可控、可调性的重要工具。但是,多数基于动态可逆作用的智能体系仅能对"开/关"转换的外界刺激因素,如光、热、溶剂、pH等产生响应,不能实现自动调控。化学振荡反应及自振荡高分子材料的发展为新型自调控智能体系的构建提供了重要的思路。本文结合自调控智能体系的最新研究进展,介绍化学振荡反应调控的动态可逆智能体系(DRIS),包括利用动态共价键、主-客体作用、配位作用、离子作用、分子间作用等动态可逆作用构筑的纳米粒子自动聚集/分散体系、两亲性分子自组装/解组装体系、宏观凝胶自组装/解组装体系、自动分子器件、自动荧光振荡体系等。最后,对化学振荡反应调控的动态可逆智能体系的研究与发展进行展望。     

天然产物凝胶及其凝胶质

天然产物是指由生物体次级代谢而产生的天然化合物。由于具有良好的生物相容性以及多种多样的药理活性, 其已被广泛应用于医药、食品、化妆品等领域。近年来, 人们发现了一类具有自组装能力的天然产物, 这些纯天然的化合物在无需修饰的情况下就能通过自组装形成一种软物质——天然产物凝胶(Natural Product Gels, NPG)。不完全等同于目前已知的凝胶(包括合成低分子质量凝胶、合成大分子凝胶和天然大分子凝胶), NPG是由天然小分子化合物(通常来源于中药)形成的超分子凝胶, 这使得NPG自身具有了良好的生物活性及对外界刺激的响应性以及具有构筑生物医药材料和刺激响应材料的内在优势。此外, 对于不同自组装NPG的生物活性改变的研究可以揭示天然产物的自组装对生物活性的影响。鉴于NPG所具有的这些特殊优势, 因此, 对其研究以及开发是具有重要的理论以及实际意义的。本文对NPG及其凝胶质的获得方法、种类、形成以及应用等方面进行了介绍, 试图让人们了解这一新兴的、跨学科的研究领域。     

气态酸和有机胺响应的超分子凝胶

超分子凝胶是由有机分子在非共价键作用力驱动下自组装形成的一种具有液态和固态双重性质的软物质。超分子凝胶能对多种外界刺激做出响应,广泛应用于催化和传感等领域。与传统的小分子探针相比,超分子凝胶传感器显示出了多种检测模式和多信号输出的优点,如超分子凝胶材料的内部三维网络结构和较大的接触面积有利于分析物的快速渗透,并且其凝胶状态的变化可以作为检测过程中的输出信号。此外,干凝胶薄膜材料还具有三维网络结构,在检测气体分析物方面表现出优异的检测性能。本文重点介绍了超分子凝胶在气态酸和有机胺检测中的应用以及相关超分子凝胶的设计和检测机理,为构建用于气态酸和有机胺检测的新型超分子凝胶提供了参考。最后总结了超分子凝胶在气态酸和有机胺检测中存在的问题及应用前景。     

响应性凝胶及其在药物控释上的应用

综述近年来在响应性凝胶材料研究方面的进展，介绍了能感应ｐＨ、温度、光、电场以及生化物质等外界因素变化的响应性凝胶的结构特点与响应机理，同时介绍了此类凝胶应用于药物控制释放方面的研究近况。     

聚合物微凝胶研究进展

微凝胶是一种具有交联网络结构的聚合物胶体粒子,处于良好溶剂中的刺激响应型微凝胶会受某些外界环境的刺激,产生溶胀-消溶胀响应行为,具有快速、可逆的相变特性和较好的生物相容性。本文综述了近年来国内外微凝胶的研究现状,介绍了互穿网络型、核-壳型和含有纳米粒子的复合型微凝胶的结构、特性和制备方法,阐述了微凝胶在药物控制释放、催化反应体系、生物传感器等方面的应用,探讨了聚合物微凝胶领域的研究前景和所面临的问题。     

Self-oscillating polymer gel as novel biomimetic materials exhibiting spatiotemporal structure

As a novel biomimetic polymer gel, we have been studying polymer gel with an autonomous self-oscillating function since it was firstly reported in 1996. For developing the polymer gels, we utilized an oscillating chemical reaction, called the Belousov?CZhabotinsky (BZ) reaction, which is recognized as a chemical model for understanding several autonomous phenomena in biological systems. The self-oscillating polymer gel is composed of a poly(N-isopropylacrylamide) network in which the metal catalyst for the BZ reaction is covalently immobilized. Under the coexistence of the reactants, the polymer undergoes spontaneous swelling?Cdeswelling changes (in the case of gel) or cyclic soluble?Cinsoluble changes (in the case of uncross-linked polymer) without any on?Coff switching of external stimuli. Several kinds of functional material systems utilizing the self-oscillating polymer and gel such as biomimetic actuators, mass transport surface, etc. are expected. Here, these recent progress on the self-oscillating polymer and gels and the design of functional material systems are summarized.     

响应性凝胶与非线性化学反应相互作用研究进展

本文综述了响应性凝胶与非线性反应动力学相互作用的研究进展,从实验及理论方面评述了pH振荡器中响应胶的振荡行为、P(NIPAAm-co-Ru(bpy)3)共聚凝胶中Belousov-Zhabotinsky(BZ)化学反应引起的膨胀-收缩振荡、行波和纳米制动器的制备及生理条件下凝胶自振荡行为,成为化学能向机械能转化的智能材料领域中活跃的研究方向; 同时凝胶的响应性作用于非线性化学反应可控制反应动力学的分岔行为.最后对该研究领域的发展方向和应用前景进行了展望.     

Fabrication of Self-Oscillating Micelles with a Built-In Oxidizing Agent

Various biological behaviors are fueled by “respiration”, which is an example of catabolism. So far, we have reported various self-oscillating soft materials exhibiting bioinspired dynamic movements. These autonomous polymer systems are driven by the Belousov–Zhabotinsky (BZ) reaction, which is analogous to the tricarboxylic acid (TCA) cycle that is an integral part of respiration. However, in the BZ reaction, the external addition of an oxidizing agent is necessary to initiate the oxidation process, which is realized by intracellular moieties such as ubiquinone in living systems. Herein, we realized self-oscillating micelles that are driven without the external addition of an oxidizing agent. This was achieved by embedding the oxidizing source into the structure of the self-oscillating AB diblock copolymers. This strategy introduces a new function equivalent to intracellular oxidizing moieties, and is useful for the design of completely autonomous bioinspired materials.     

Photomechanics of liquid-crystalline elastomers and other polymers

Muscle is a transducer that can convert chemical energy into mechanical motion. To construct artificial muscles, it is desirable to use soft materials with high mechanical flexibility and durability rather than hard materials such as metals. For effective muscle-like actuation, materials with stratified structures and high molecular orders are necessary. Liquid-crystalline elastomers (LCEs) are superior soft materials that possess both the order of liquid crystals and the elasticity of elastomers (as they contain polymer networks). With the aid of LCEs, it is possible to convert small amounts of external energy into macroscopic amounts of mechanical energy. In this Review, we focus on light as an energy source and describe the recent progress in the area of soft materials that can convert light energy into mechanical energy directly (photomechanical effect), especially the photomechanical effects of LCEs with a view to applications for light-driven LCE actuators.     

Self-driven gel conveyer: effect of interactions between loaded cargo and self-oscillating gel surface

A "self-oscillating" gel that swells and deswells periodically under constant conditions is developed as a novel biomimetic gel differing from conventional stimuli-responsive polymer gels. By utilizing the peristaltic motion of the self-oscillating gel, autonomous mass-transport systems can be realized. With the propagation of the chemical wave, the loaded gel cargo is autonomously transported by rotating on the surface. To apply the self-driven gel conveyer to a wider range of uses, it is important to investigate the influence of the physical interaction between the self-oscillating gel and the loaded cargo on its transporting ability. Here, the effect of the interaction is evaluated by using several kinds of gel cargo with varying charge states, hydrophilicities, and surface roughnesses.     

Self-oscillating gels based on novel catalyst for the Belousov–Zhabotinsky reaction

We report on the synthesis of new Ru(bpy)₂(phen) catalyst for the oscillatory Belousov–Zhabotinsky chemical reaction and on the preparation of novel Ru(bpy)₂(phen)-based self-oscillating gels. The synthesized gels exhibit high-amplitude autonomous mechanical oscillations when the Belousov–Zhabotinsky reaction proceeds inside these gels     

Reinforcement of cellulose nanofibers in polyacrylamide gels

Cellulose nanofibers (CNFs) have emerged as a promising nanofiller for effective reinforcement of nanocomposites due to their excellent mechanical properties. In this study, CNFs were fabricated by a simple grinding method and used to strengthen polyacrylamide (PAM) gels through in situ free radical polymerization. The morphology, compression properties, and chemical structure of the prepared gels were investigated. The results showed that large amounts of nanofibers embedded inside the PAM matrix and formed network structure by increasing the CNF content. Significantly, PAM/CNF gel with 5 wt% CNF exhibited highly improved compression strength by 6.8-fold as compared to that of pure PAM gel. The FTIR analysis indicated that hydrogen bondings between CNF and PAM chains mainly contributed to the superior mechanical properties of the hybrid gels. In summary, this study provides a novel alternative approach for preparing tough composite gels by combing rigid CNF and soft polymer and extending the application of biomedical load-bearing gel materials such as artificial cartilage and other soft tissues.     

Self-oscillation of polymer chains induced by the Belousov-Zhabotinsky reaction under acid-free conditions

A novel self-oscillating polymer was prepared by utilizing the Belousov-Zhabotinsky (BZ) reaction. In this study, a sulfonic acid group was newly introduced as a pH-control site into the copolymer of N-isopropylacrylamide, and the ruthenium complex was introduced as a catalyst site. By introducing the pH-control site, we succeed in causing the soluble-insoluble self-oscillation of the polymer solution under acid-free conditions in which only two BZ substrates, malonic acid and sodium bromate, were present as added agents. The self-oscillating behavior was remarkably influenced by the temperature and polymer concentration, which reflects the intermolecular aggregative capacity of the polymer chains in the reduced state to change the lower critical solution temperature. This achievement of self-oscillation of polymer chains under acid-free conditions may lead to their practical use as novel biomimetic materials under biological conditions.     

Click-Formed Polymer Gels with Aggregation-Induced Emission and Dual Stimuli-Responsive Behaviors

Stimuli-responsive polymer gels have recently attracted great attention due to their heat/solvent resistance, dimensional stability, and unique sensitivity to external stimuli. In this work, we synthesized thiol-functionalized tetraphenylethylene (TPE) and constructed polymer gels through thiol-ene click reaction. The synthetic process of the polymer gels could be monitored by fluorescence emission of TPE moieties based on aggregation-induced emission mechanism. In addition, due to the dual redox- and acid responsiveness of the polymer gels, in the presence of dithiothreitol and trifluoroacetic acid, fluorescence quenching of the polymer gels can be observed. This stimuli-responsive characteristics endows the polymer gels with potential applications in fluorescent sensing and imaging, cancer diagnosis and selfhealing materials.