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Photoswitchable Supramolecular Hydrogels Formed by Cyclodextrins and Azobenzene Polymers
Angewandte Chemie International Edition
Abstract
Shine a light: A supramolecular hydrogel is formed by the glucan curdlan equipped with α-cyclodextrins (CD-CUR) and azobenzene-modified poly(acrylic acid)(pAC12Azo). The sol-gel transition and the morphology of the supramolecular hydrogel can be switched by photoirradiation at the appropriate wavelength, which controls the formation of an inclusion complex between the α-cyclodextrins and the azobenzene moieties (see picture).
... 。根据水凝胶内部光响应基元不同，光响应性水凝胶可 以分为：(1)光反应型水凝胶 [10] ，通过光照发生一定的化学反应(光交联、光降解等)从而影响水凝胶的物理化 学性质，通常光反应是不可逆的，限制了这类水凝胶的多次循环利用；(2)光热型水凝胶 [8,11] ，通过光热组分将 光能转换成热能，间接改变水凝胶的结构和性能，一般使用强光照，且仅适用于热响应性水凝胶体系；(3)光 开关型水凝胶 [12][13][14][15] ，由分子开关或分子机器的光致可逆异构化调控水凝胶宏观形态和性能，通常所用光照强 度较弱，不会带来明显光热效应，具备高度循环利用特性，因此受到越来越多的关注，成为光响应性水凝胶中的 明星。本综述将重点围绕光开关型水凝胶的分子设计、制备以及仿生驱动等方面展开讨论，着重介绍含偶氮苯、 旋转分子马达、二芳基乙烯、螺吡喃等(图1)光响应性水凝胶的发展和现状，并对其应用和发展趋势进行展望。 1 含偶氮苯光响应水凝胶 偶氮苯作为一类最经典的光开关分子，具有顺式(cis)和反式(trans)两种异构体，可在紫外和可见光的照 射下实现可逆转换 [16] 。两种异构体的分子构型、偶极矩等理化性质存在明显差异，因此可以利用偶氮苯的光 致异构化直接或间接调控分子聚集形态和材料宏观结构性能，代表工作包括光致液晶分子晶相-无定形相之 间的转化 [17][18][19] 、光致凝胶剂分子凝胶-溶胶转变等 [20] 。此外，偶氮苯作为一个明星客体分子，反式异构体与环 糊精等大环主体化合物存在较强的主客体识别作用，而顺式偶氮苯由于尺寸不匹配无法发生主客体识别 [21] 光响应液晶高分子材料 [17] 。基于相似原理，人们将偶氮苯分子用作桥连单元，把亲水、疏水片段连接起来形 成具有组装能力的两亲性凝胶剂分子(gelator)，从而实现凝胶-溶胶之间的光致可逆转变，并被用做光致可控 药物释放体系。例如，Zhang课题组 [22] 报道了一种由偶氮苯桥连的二价吡啶阳离子化合物，当偶氮苯处于反 式结构时可组装形成凝胶，紫外光照射后变成溶胶状态(图2(a))。这种光控偶氮苯异构化实现凝胶-溶胶转 变的策略被拓展到多种分子体系，分别实现了包括寡糖 [23,24] 、多肽 [25] 和DNA等凝胶剂分子的构筑 [26,27] ，其 中图2(b)展示了Pianowski课题组 [28] 发展的光敏自修复超分子水凝胶，应用于光诱导DNA和阿霉素释放。 此外，平面型的反式偶氮苯分子可通过与核酸碱基形成π-π堆积，从而稳定插入到DNA双螺旋结构，而 顺式异构体由于结构卷曲和空间位阻效应，会严重破坏DNA碱基互补配对，这一特性被Tan课题组 [29] 用来 调控DNA水凝胶网络的光致动态交联和解交联(图2(c))，实现了水凝胶体积的光致收缩和溶胀。值得注意 的是，偶氮苯分子也被Anseth课题组 [30] ...
... 图 2 含偶氮苯凝胶剂的光致凝胶-溶胶转变(a) [22] ；含偶氮苯超分子水凝胶的DNA释放(b) [28] ；含偶氮苯DNA水凝胶的溶胀-收缩(c) [29] ；交联型偶氮苯异构化调节水凝胶力学强度(d) [30] Fig. 2 Sol-gel transition of azobenzene-containing hydrogelators triggered by light (a) [22] ; DNA release by azobenzene-containing supramolecular hydrogels (b) [28] ; Volume expansion-contraction of azobenzene-containing DNA hydrogels (c) [29] ; Tunable mechanical strength of hydrogels induced by azobenzene isomerization (d) [30] 第 [36] ；基于环糊精-偶氮苯聚轮烷的人工肌肉(c) [38] Photoinduced expansion-contraction of azobenzene-and α-CD-containing hydrogels (b) [36] ; Artificial muscles formed by azobenzenebased polyrotaxanes (c) [38] 偶氮苯和环糊精合成到聚轮烷结构中，通过光照调控主客体之间的结合和解离进而带动聚轮烷的正向或反 向滑动，最终调控整个交联网络的舒张和收缩(图3(c))。具体来说，环糊精-反式偶氮苯发生主客体识别后 使聚轮烷呈舒张状态进而带动交联网络膨胀，反之，紫外光照射促使主客体识别作用发生解离，进而使交联 结构发生收缩。因此，基于聚轮烷的人工肌肉材料在紫外光的照射下表现出向光弯曲行为，这与之前依靠主 客体识别作用作为额外交联点的体系在紫外光下的背光弯曲行为恰好相反。 2 含二芳基乙烯光响应水凝胶 二芳基乙烯类化合物在不同吸收波长光的照射下，能够发生开环体与闭环体之间的可逆转化，具有良好 的热稳定性和抗疲劳性，在光致变色、光电信息存储等领域有着重要应用 [39][40][41] 。Zhang课题组 [42] 利用开环和 闭环二噻吩乙烯在分子构型、刚性以及与凝胶剂L-苯丙氨酸共组装等方面的显著差异，设计合成了一类光致 凝胶-溶胶转变的超分子体系，实现了可见光驱动的移液器内无电位、无创的单细胞注射和药物递送(图4(a))。 图 4 基于二芳基乙烯的光致凝胶-溶胶转变(a) [42] ；联吡啶-二芳基乙烯介导的水凝胶形状记忆(b) [44] ；二芳基乙烯介导的金属-有机笼高分子网络拓扑结构改变(c) [45] Fig. 4 Photoinduced sol-gel transition based on diarylethylene (a) [42] ; Shape memory effect of bipyridine-diarylethylene containing hydrogel (b) [44] ; Diarylethylene-mediated topology change of metal-organic cage containing polymer network (c) [45] 第 3 期 廖 聪，等：光响应性水凝胶的分子设计和仿生驱动 Liu等通过静电相互作用将二芳基乙烯桥联的双吡啶盐引入到无机纳米黏土水凝胶中，利用无机纳米框架限 制分子转子的自由旋转，从而得到了具有荧光发光性质的水凝胶 [43] 。Willner等 [44] 利用联吡啶双二烯基乙烯 图 5 紫外光驱动的分子马达微观转动导致凝胶宏观收缩(a) [49] ；整合分子马达和调制器的紫外-可见光可逆响应凝胶(b) [50] ；分 子马达自组装形成光敏超分子水凝胶人工肌肉(c) [51] ；分子马达自组装形成光敏水凝胶用于干细胞培养(d) [53] Fig. 5 Macroscopic contraction of the gel induced by ultraviolet light triggered microscopic rotation of the molecular motor (a) [49] ; Reversible contraction-expansion of the gel integrating molecular motors and modulators upon irradiation by UV and visible light (b) [50] ; ...
... 图 2 含偶氮苯凝胶剂的光致凝胶-溶胶转变(a) [22] ；含偶氮苯超分子水凝胶的DNA释放(b) [28] ；含偶氮苯DNA水凝胶的溶胀-收缩(c) [29] ；交联型偶氮苯异构化调节水凝胶力学强度(d) [30] Fig. 2 Sol-gel transition of azobenzene-containing hydrogelators triggered by light (a) [22] ; DNA release by azobenzene-containing supramolecular hydrogels (b) [28] ; Volume expansion-contraction of azobenzene-containing DNA hydrogels (c) [29] ; Tunable mechanical strength of hydrogels induced by azobenzene isomerization (d) [30] 第 [36] ；基于环糊精-偶氮苯聚轮烷的人工肌肉(c) [38] Photoinduced expansion-contraction of azobenzene-and α-CD-containing hydrogels (b) [36] ; Artificial muscles formed by azobenzenebased polyrotaxanes (c) [38] 偶氮苯和环糊精合成到聚轮烷结构中，通过光照调控主客体之间的结合和解离进而带动聚轮烷的正向或反 向滑动，最终调控整个交联网络的舒张和收缩(图3(c))。具体来说，环糊精-反式偶氮苯发生主客体识别后 使聚轮烷呈舒张状态进而带动交联网络膨胀，反之，紫外光照射促使主客体识别作用发生解离，进而使交联 结构发生收缩。因此，基于聚轮烷的人工肌肉材料在紫外光的照射下表现出向光弯曲行为，这与之前依靠主 客体识别作用作为额外交联点的体系在紫外光下的背光弯曲行为恰好相反。 2 含二芳基乙烯光响应水凝胶 二芳基乙烯类化合物在不同吸收波长光的照射下，能够发生开环体与闭环体之间的可逆转化，具有良好 的热稳定性和抗疲劳性，在光致变色、光电信息存储等领域有着重要应用 [39][40][41] 。Zhang课题组 [42] 利用开环和 闭环二噻吩乙烯在分子构型、刚性以及与凝胶剂L-苯丙氨酸共组装等方面的显著差异，设计合成了一类光致 凝胶-溶胶转变的超分子体系，实现了可见光驱动的移液器内无电位、无创的单细胞注射和药物递送(图4(a))。 图 4 基于二芳基乙烯的光致凝胶-溶胶转变(a) [42] ；联吡啶-二芳基乙烯介导的水凝胶形状记忆(b) [44] ；二芳基乙烯介导的金属-有机笼高分子网络拓扑结构改变(c) [45] Fig. 4 Photoinduced sol-gel transition based on diarylethylene (a) [42] ; Shape memory effect of bipyridine-diarylethylene containing hydrogel (b) [44] ; Diarylethylene-mediated topology change of metal-organic cage containing polymer network (c) [45] 第 3 期 廖 聪，等：光响应性水凝胶的分子设计和仿生驱动 Liu等通过静电相互作用将二芳基乙烯桥联的双吡啶盐引入到无机纳米黏土水凝胶中，利用无机纳米框架限 制分子转子的自由旋转，从而得到了具有荧光发光性质的水凝胶 [43] 。Willner等 [44] 利用联吡啶双二烯基乙烯 图 5 紫外光驱动的分子马达微观转动导致凝胶宏观收缩(a) [49] ；整合分子马达和调制器的紫外-可见光可逆响应凝胶(b) [50] ；分 子马达自组装形成光敏超分子水凝胶人工肌肉(c) [51] ；分子马达自组装形成光敏水凝胶用于干细胞培养(d) [53] Fig. 5 Macroscopic contraction of the gel induced by ultraviolet light triggered microscopic rotation of the molecular motor (a) [49] ; Reversible contraction-expansion of the gel integrating molecular motors and modulators upon irradiation by UV and visible light (b) [50] ; ...
... The hydrogel exhibits three-dimensional (3D) nanofibrous networks with the ability to assemble and disassemble due to light resulting from the photoisomerization of azobenzene motifs. [48] This is an interesting phenomenon to observe in the hydrogel in their two states of sol-gel and gel-sol switching depending upon the wavelength of light to switch the cis and trans isomers of the azobenzene motif in the polymer as shown in Figure 8. [49] Many research areas in chemistry are connected with each other, for example, host-guest systems are also used in surface chemistry to modify the surfaces or make them functional for the different perspectives of applications. For example, Roling et al. reported the surface immobilization of azobenzenecontaining polymers on a glass surface with β-cyclodextrin polymers through surface-initiated atom transfer radical polymerization (ATRP) and resultantly two surfaces glued together [50] (Figure 9). ...
... Schematic illustration of azobenzene-containing polymers as guest and CD polymer as host, formation of hydrogel and association between two components, and disassembly of hydrogel and dissociation of two components. Reproduced from ref.[49] Copyright (2010), with permission from Wiley-VCH. ...
Azobenzene-containing small molecules and polymers are functional photoswitchable molecules to form supramolecular nanomaterials for various applications. Recently, supramolecular nanomaterials have received enormous attention in material science because of their simple bottom-up synthesis approach, understandable mechanisms and structural features, and batch-to-batch reproducibility. Azobenzene is a light-responsive functional moiety in the molecular design of small molecules and polymers and is used to switch the photophysical properties of supramolecular nanomaterials. Herein, we review the latest literature on supramolecular nano- and micro-materials formed from azobenzene-containing small molecules and polymers through the combinatorial effect of weak molecular interactions. Different classes including complex coacervates, host-guest systems, co-assembled, and self-assembled supramolecular materials, where azobenzene is an essential moiety in small molecules, and photophysical properties are discussed. Afterward, azobenzene-containing polymers-based supramolecular photoresponsive materials formed through the host-guest approach, polymerization-induced self-assembly, and post-polymerization assembly techniques are highlighted. In addition to this, the applications of photoswitchable supramolecular materials in pH sensing, and CO2 capture are presented. In the end, the conclusion and future perspective of azobenzene-based supramolecular materials for molecular assembly design, and applications are given.
... The proposed model also accounts for the cis-to-trans isomerization under visible light or due to the thermal relaxation and corresponding formation of the host-guest supramolecular complexes between the trans-azobenzene moieties and a-CD units. [57][58][59] The models capturing the isomerization of azobenzene moieties typically consider three processes: UV-driven trans-to-cis photoisomerization, the visible light-driven cis-to-trans photoisomerization, and the spontaneous trans-to-cis thermal relaxation as following 19,60-63 : trans-Azo ...
... 25 Since the absorption spectra of trans and cis isomers of azobenzene moieties overlap substantially, a single wavelength of light can activate both forward and reverse photoisomerzation and results in a mixed photostationary state: maximum of approximately 80% cis-Azo upon UV light or 95% trans-Azo upon visible light. 18,58,72 We select the reference values of rate constants as listed in Table 1. These values are chosen within the range for the photoisomerization and thermal relaxation of azobenzene derivatives incorporated into the polymers, specifically within the range of 10 À 4 $ 10 À 2 s À 1 for k tc and k ct (Ref. ...
Patterns formed under external stresses are often critical for ensuring functionality of soft materials. We focus on dynamic control of pattern formation and restructuring in hydrogels with host-guest interactions. We extend three-dimensional gel Lattice Spring Model to capture the dynamics of photo-responsive hydrogels with pendant azobenzene moieties immersed in the α-cyclodextrin (α-CD) solution. While trans-azobenzene moieties are accommodated by the α-CD cavities forming inclusion complexes resulting in hydrogel swelling, an exposure to UV irradiation induces trans-to-cis photoisomerization leading to decomplexation and matrix deswelling. We demonstrate swelling-induced patterns in confined samples upon adding the α-CD solution in the dark. Further, we show that spatiotemporal variations in UV irradiation effectively control patterns formed and hysteresis loops. We introduce soft confinements via illuminating specific regions of unconstrained samples with UV light. Our results indicate that features of patterns and hysteresis in systems’ response to external conditions can be regulated via well-defined illumination patterns.
... Due to their usefulness, various stimuli-responsive materials have been enthusiastically studied and reported. For example, photo-responsive gel materials can be formed by using polymers having the side chains interacting via host-guest interactions [30]. The gel composed of a polymer having cyclodextrins and a polymer having azobenzene moieties as side chains shows photo-responsive sol-gel transitions, adhesion, and actuating motion. ...
A self-healing gel with self-healing kinetics that can be regulated by heat is developed. The gel is composed of a polymer having benzophenone (BP) substituents, which are cross-linked with a main alkyl chain via ester bonds, titanium chloride, and zinc. This gel material shows a self-healing property at room temperature. Also, its self-healing behavior can be accelerated by heating the gel. This gel having self-healing kinetics that can be regulated by heat is favorable for practical use. When we want to use a self-healing property as a stop-gap measure, a rapid self-healing property is demanded. On the other hand, when we want materials repaired beautifully or decomposed surfaces need to be attached beautifully, a slow self-healing property is favorable. These opposite demands can be answered by the gel with self-healing kinetics that can be regulated by heat.
... Propriétés biologiquesCertains travaux scientifiques se sont intéressés à la synthèse de polyrotaxanes hydrogels photosensibles pour le relargage contrôlé de molécules biologiques. Une diversité de systèmes photocontrolés de cette nature formés par inclusion de polymères d'azobenzène dans la cavité hydrophobe de cyclodextrines a été étudiée141,142 . En 2015, l'équipe de Wu développe un polyrotaxane hydrogels capable de s'assembler en présence d'un dérivé polymérique d'azobenzène trans s'incluant au sein de β-cyclodextrines143 . ...
... Therefore, the dye and cyclodextrin form crosslinks that are reversible under irradiation with light of suitable wavelength. As a consequence, it is possible to switch between the sol-and the gel-state [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. ...
The unique photomotion of azo materials under irradiation has been in the focus of research for decades and has been expanded to different classes of solids such as polymeric glasses, liquid crystalline materials, and elastomers. In this communication, azo dye-containing gels are obtained by photocrosslinking of non-thermoresponsive and lower critical solution temperature type thermoresponsive copolymers. These are analysed with light microscopy regarding their actuation behaviour under laser irradiation. The influences of the cloud-point temperature and of the laser power are investigated in a series of comparative experiments. The thermoresponsive hydrogels show more intense photoactuation when the cloud-point temperature of the non-crosslinked polymer is above, but closer to, room temperature, while higher laser powers lead to stronger motion, indicating a photothermal mechanism. In non-thermoresponsive gels, considerably weaker photoactuation occurs, signifying a secondary mechanism that is a direct consequence of the optical field-azo dye interaction.
... Nowadays, a new frontier is achievable in combining well-known photochromic units with different supramolecular hosts and, on this regard, one of the most promising and thoroughly investigated combination is the association between the E and Z forms of the azobenzene unit [9] with cyclodextrins [10]. Among the different achievements obtained by these systems, developments in the fields of photoswitchable supramolecular hydrogels [11], UV responsive supramolecular nanofibers [12] and photoswitchable catalysts [13] clearly state the advances reached in the comprehension and design of such approach. ...
The supramolecular interactions in water between β-cyclodextrin and the open and closed photochromic forms of two bis-cationic dithienylethenes, characterized by different electronic properties, were investigated aiming at underlying the key aspects of the recognition process. The dithienylethene equipped with the cyclopentenyl unit showed a difference in binding free energies to the β-cyclodextrin between the open and closed photochromic forms of about 1 kJ/mol. Conversely, the dithienylethene equipped with the perfluorinated cyclopentenyl unit not only was a better guest but showed a three times higher difference in the binding of free energies between the open and closed isomers.
This review introduces the response mechanism of photoresponsive lanthanide luminescent materials. In particular, various applications in luminescent actuators, photoswitches, intelligent anticounterfeiting, and theranostics are highlighted.
A series of tetra-coordinate boron-peptide conjugates has been reported. The incorporation of a photochromic organoboron unit into the gelator endows photoactivity to the supramolecular gels. While the structural transformation of...
Azobenzene-based probes have been widely utilized in biosensing, bioimaging and nanomedicine, while the water solubility was not good enough, especially for the processes which go through a long term. To...
Light‐driven actuators are widely used for smart devices such as soft robots. One of the main challenges for actuators is achieving rapid responsiveness, in addition to ensuring favorable mechanical properties. Herein, we focused on photoresponsive polyurethane (CD‐Azo‐PU) based on controlling the crystallization of the hard segments in polyurethane (PU) by complexation between azobenzene (Azo) and cyclodextrins (CDs). CD‐Azo‐PU incorporated polyurethane as the main chain and a 1:2 inclusion complex between Azo and γCD as a movable crosslink point. Upon ultraviolet light (UV, λ = 365 nm) irradiation, the photoresponsiveness of CD‐Azo‐PU bent toward the light source (defined as positive), while that of the linear Azo polyurethane (Azo‐LPU) without peracetylated γ‐cyclodextrin diol (TAcγCD‐diOH) as a movable crosslinker bent in the direction opposite the light source. The bending rates were determined to be 0.25°/s for CD‐Azo‐PU and 0.083°/s for Azo‐LPU, indicating that the bending rate for CD‐Azo‐PU was faster than that for Azo‐LPU. By incorporating movable crosslinks into CD‐Azo‐PU, we successfully achieved specific photoresponsive actuation with an enhanced rate.
Multicellular organisms demonstrate a hierarchical organization where multiple cells collectively form tissues, thereby enabling higher‐order cooperative functionalities beyond the capabilities of individual cells. Drawing inspiration from this biological organization, assemblies of multiple protocells are developed to create novel functional materials with emergent higher‐order cooperative functionalities. This paper presents new artificial tissues derived from multiple vesicles, which serve as protocellular models. These tissues are formed and manipulated through non‐covalent interactions triggered by a salt bridge. Exhibiting pH‐sensitive reversible formation and destruction under neutral conditions, these artificial vesicle tissues demonstrate three distinct higher‐order cooperative functionalities: transportation of large cargoes, photo‐induced contractions, and enhanced survivability against external threats. The rapid assembly and disassembly of these artificial tissues in response to pH variations enable controlled mechanical task performance. Additionally, the self‐healing property of these artificial tissues indicates robustness against external mechanical damage. The research suggests that these vesicles can detect specific pH environments and spontaneously assemble into artificial tissues with advanced functionalities. This leads to the possibility of developing intelligent materials with high environmental specificity, particularly for applications in soft robotics.
Effective wound management is important, as millions of people suffer traumatic injuries and surgical operations annually. Proper wound closure is essential for the structural and functional restoration of damaged tissues. In addition to conventional sutures, various advanced surgical materials with multiple functions have been developed for more reliable and improved wound healing performance in the past few years. Here, polymeric surgical materials for soft tissue wound closure are comprehensively reviewed, including both commercially available materials and newly developed materials. These materials, based on natural, synthetic or composite polymers, are classified and discussed as invasive and non-invasive surgical materials. Their properties (antibacterial, hemostatic, stimuli-responsive, drug delivery, or a combination thereof) are critically analysed in the context of improving wound healing. Moreover, how to tune these properties (e.g., chemical grafting of antibacterial moieties, nano-enabled regulation of hemostasis, dual stimuli-responsive design, etc.) are clearly discussed. Finally, challenges in the field and potential solutions to tackle them are also proposed. This review should inspire more research efforts to develop the next generation of promising surgical polymeric materials for clinical applications.
In this work, a hydrophobic guest monomer containing adamant end‐group was synthesized and introduced into the acrylamide hydrogel system to prepare macroscopic guest hydrogel. The swelling, transparency, and mechanical properties of the guest hydrogels can be significantly changed by soaking the guest hydrogel into hydrophilic cyclodextrin solution because the hydrophobic guest groups were recognized and covered by the hydrophilic host molecules. In addition, the surface lubrication property could be adjusted by changing the proportion of acrylamide and adamantane monomers in the hydrogel system. More importantly, cyclodextrin can bind with adamantane through host‐guest interactions, enabling the adjustment of the hydrophilicity/hydrophobicity properties of the hydrogel system. By controlling the assembly time, the hydrogel with different lubrication behaviors can be obtained. The controllable surface friction that this specific binding of host‐guest interaction has broad application prospects in intelligent device, bionic lubrication and other fields.
Lanthanide-derived flexible luminescent hydrogels have attracted attention due to their unique physical, chemical, and biological properties, which enable the construction of functional and architecturally designed materials inspired by nature. This comprehensive review provides insight into the design principles and fabrication strategies for the coordination self-assembly of lanthanide-derived supramolecular hydrogels, outlines the fundamental properties and the importance required in optical and biological fields, summaries recent advances of these hydrogels for multifunctional flexible material construction, and discusses their applications in environmental and medical fields including stimuli responsiveness, chemo-biosensing, luminescence anisotropy, 3D printing, self-healing, and anti-counterfeiting. The objective of this review is to provide useful insights that can advance the development of next-generation bioelectronics and facilitate the connection between luminescent hydrogels as fundamental and multi-functional optical materials for various applied targets. Ultimately, this review aims to accelerate new material design by highlighting recent advances in lanthanide-derived supramolecular hydrogels.
Conductive gels have gained attention from researchers due to potential applications in flexible displays, implantable medical devices, touch panels, wearable electronic skin, sensors, soft robotics, etc. A photo-responsive conductance switching...
In nature, plants and animals undergo remodeling to adapt to changes in their surroundings. Stimuli-responsive hydrogels, with their abundant water content and inherent responsiveness to environmental stimuli, serve as ideal...
This review focuses on solvent‐free molecular liquid materials that exhibit changes in response to stimuli. Along with the recent development of soft functional materials, research on functional liquids possessing free deformability and ease of molding is becoming a new trend. A typical method for designing functional molecular liquids (FMLs) introduces flexible alkyl side‐chains around a π‐conjugation unit at the center of the molecule. As a result, the aggregation between π‐conjugated units is inhibited, and an entropy‐rich room temperature liquid is obtained. FMLs designed in this way can exhibit unique and exciting stimulus responses due to the high density of functional units and fluidity. Such notable features include electrochromism, phase transitions, and dynamic changes in the nanostructure. In addition, some stimulus responses are reversible and thanks to the fluidity, return to their initial state under relatively mild conditions, such as room temperature or slight heating. To elicit such effective stimulus responses, selecting an optimal π‐core, and modifying it with the appropriate alkyl side‐chains (length, branching, and substitution position) is essential. A deep understanding of the alkyl–π molecular design will enable the creation of more attractive stimuli‐responsive FMLs, which are of high value in advanced fields such as healthcare, security, sensors, soft electronics, and robotics.
Supramolecular gels are promising as chemosensors, drug delivery systems and oil gelators. The present paper deals with photoluminescent supramolecular gels derived from phenylenediamine hydrochlorides. N-(3,5-Diaminobenzoyl)-L-alanine dodecyl ester dihydrochlorides (1L) underwent gelation in tetrahydrofuran (THF) and CHCl3, but not in C1-C4 alcohols, dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF). Compound 1L emitted blue fluorescence in the sol state and green fluorescence in the gel state. A THF solution of 1L exhibited absorption and emission maxima at wavelengths 94-104 nm and 92-110 nm longer than those in other solvents, such as methanol and ethanol, that cause no gelation of 1L. Particles with hydrodynamic diameters around 13 nm were detected in a THF solution (c = 1.0 mM) of 1L. The gelation of 1L in THF and CHCl3, and the lack of gelation in MeOH were supported by molecular dynamics simulations and dynamic light scattering measurements. N-(3,5-Diaminobenzoyl)-L-alanine dodecyl ester (1L'), an HCl-free analogous compound of 1L, underwent no gelation in THF and CHCl3, indicating the necessity of the ammonium salt structure for gelation. The UV-vis absorption and photoluminescence spectroscopic peaks of 1L red-shifted upon aggregation, which was supported by TD-DFT calculations of monomeric and dimeric models of 1L.
Adhesive gel systems are attracting increasing interest from researchers to use gel materials for artificial biomaterials and engineering materials. Humans, among other living beings, eat foods, get nutrients from them, and use these nutrients to grow up day by day. The shapes and characteristics of their bodies change depending on the nutrients they get. This research develops an adhesive gel system that the chemical structure of the adhesive joint and their properties can be changed and regulated after adhesion, like the growth of living beings. The adhesive joint, which is constructed using a linear polymer comprising a cyclic trithiocarbonate monomer and acrylamide, developed in this research reacts with amines and forms chemical structures depending on amines. The differences in chemical structures endow the adhesive joint with the characteristics and properties that depend on the reaction of amines with the adhesive joint.
The field of tissue engineering and regenerative medicine has been evolving at a rapid pace with numerous novel and interesting biomaterials being reported. Hydrogels have come a long way in this regard and have been proven to be an excellent choice for tissue regeneration. This could be due to their innate properties such as water retention, and ability to carry and deliver a multitude of therapeutic and regenerative elements to aid in better outcomes. Over the past few decades, hydrogels have been developed into an active and attractive system that can respond to various stimuli, thereby presenting a wider control over the delivery of the therapeutic agents to the intended site in a spatiotemporal manner. Researchers have developed hydrogels that respond dynamically to a multitude of external as well as internal stimuli such as mechanics, thermal energy, light, electric field, ultrasonics, tissue pH, and enzyme levels, to name a few. This review gives a brief overview of the recent developments in such hydrogel systems which respond dynamically to various stimuli, some of the interesting fabrication strategies, and their application in cardiac, bone, and neural tissue engineering.
Hydrogels are highly hydrated three dimensional networks with the ability to mimic the extracellular matrix of bodily tissues and have thus found application in a wide range of biomedical applications. Unique physiochemical properties such as biocompatibility, water permeability, stimuli responsiveness and self-healing characteristics make them especially useful for use as scaffolds and matrices drug delivery, tissue engineering/regeneration and sensing. Their weak and brittle nature, however, often limits their widespread application where improved mechanical strength is required.
To resolve this problem, there has been a significant amount of research into the improvement of their mechanical properties. Among these efforts, versatile multicomponent hydrogels have received much attention as their physiochemical properties can be structurally engineered to provide a wide range of desired properties. These multicomponent formulations also allow for the combination of natural and synthetic polymers, which offers the scope to exploit the advantages of each component, with the synergistic effects resulting from mutual interactions.
This book critically discusses the fundamental chemistry, synthesis, characterisation, physiochemical and biological properties of various types of multicomponent hydrogels. It reviews the different strategies employed in designing and synthesizing cutting-edge multicomponent hydrogels and their key applications in biomedical fields.
The work is suitable for researchers working in the specific area of multicomponent hydrogels, and also more generally for those working in materials science, biomedical engineering, biomaterials science and tissue engineering.
Stimuli‐responsive or smart materials have recently shown a significant impact on the frontier of material science and engineering. The exponential development of synthetic host molecules (SHMs) over the last decades and their corresponding host–guest chemistry, have empowered researchers with new opportunities to design and construct tailored or guest‐specific smart materials. In this Minireview, we present the recent advancements in synthetic host based smart materials, ranging from the fabrication strategies to the state‐of‐art applications including adsorption, separation, luminescence, self‐healing and actuation. The role that the host–guest chemistry plays in these systems is highlighted throughout to give a better prospective of the available possibilities for emerging materials of future economies.
Stimuli‐responsive or smart materials have recently shown a significant impact on the frontier of material science and engineering. The exponential development of synthetic host molecules (SHMs) over the last decades and their corresponding host–guest chemistry, have empowered researchers with new opportunities to design and construct tailored or guest‐specific smart materials. In this Minireview, we present the recent advancements in synthetic host based smart materials, ranging from the fabrication strategies to the state‐of‐art applications including adsorption, separation, luminescence, self‐healing and actuation. The role that the host–guest chemistry plays in these systems is highlighted throughout to give a better prospective of the available possibilities for emerging materials of future economies.
Glaucoma is the leading cause of irreversible blindness, and its treatment is attracting widespread attention. Drug-loaded lacrimal suppositories can effectively treat xerophthalmia, but there is little research on the treatment of glaucoma with drug-loaded lacrimal suppositories. This article explored and expanded the non-pharmacological model of lacrimal suppository therapy for glaucoma by using a combination of lacrimal suppository and medication. The drug-loaded lacrimal suppository was rationally designed through the conjugation of gelatin with polyamide (PAM) via the formation of amide linkages, followed by Schiff base reaction grafting with latanoprost. In vitro drug release studies showed that latanoprost released from drug-loaded lacrimal embolus had sustained-release properties with a release time of 33 days and a drug release volume of 82.6%. The biological evaluation of drug-loaded lacrimal thrombus was carried out by IOP test, retinal potential test, and retinal H&E staining. The results showed that the IOP decreased to 27.125 ± 1.1254 mmHg, and the a and b waves of retinal potential increased to 4.39 ± 0.16 μV and 67.9 ± 2.17 μV, respectively. It indicated that latanoprost lacrimal suppository has a good therapeutic effect on glaucoma.
Our aim in this thesis is to build dissipative life-like materials using photoredox of perylene bisimide (PBI) under ambient conditions. The main challenge in PBI photoreduction is that only one-electron transfer allows to be photoinduced under vacuum conditions. To drive the aggregated PBI away from equilibrium, our research is divided into four parts. First, we built the electron donor-acceptor system in which the photoinduced two-electron transfers in aggregated PBI, whereas one-electron transfers in monomer under vacuum conditions. Secondly, we significantly accelerated PBI photoreduction by introducing a UV-activated chemical fuel under ambient conditions, which opens possibilities to achieve different non-equilibrium steady states. Thirdly, we developed a dual-functional fuel DTT being an electron both in PBI chemical and photoreduction, which allows us to construct PBI transient aggregates, and observe emergent properties, such as oscillation. Lastly, we developed the PBI photoreduction from its solution to gels that can be selectively photoinduced one or two-electron transfer. These chemical fuels provide PBI a leading role in developing light-driven out-of-equilibrium materials.
We report a new strategy that allows reversible tuning of the stiffness and stress-relaxation of viscoelastic hydrogels cross-linked via hydrazone bonds by incorporating a small-molecule competitor. The competitor molecule competes for the formation of reversible hydrazone bonds and temporarily reduces the cross-linking density in the hydrogel, thus softening the hydrogel and accelerating its stress-relaxation. By rapidly diffusing the competitor in and out of the hydrogel, the mechanical properties of hydrogels can be reversibly altered over many cycles. We further examined the biocompatibility of the competitor and explored its application in cell delivery via injection by temporarily adjusting the hydrogel mechanical properties to improve cell viability during the injection.
Nowadays, supramolecular hydrogels have gained special importance and development of versatile approaches for their preparation as well as their new facile characterization strategies has elicited tremendous scientific interest. Herein, we demonstrate that modified cellulose nanowhisker with gallic acid pendant groups (CNW-GA) could effectively bind with CNW grafted with β-Cyclodextrin (CNW-g-β-CD) through HG interaction to form fully biocompatible and low-cost supramolecular hydrogel. Also, we reported an easy and efficient colorimetric characterization method for confirming HG complexation using naked eye. The possibility of this characterization strategy evaluated both experimentally and theoretically using DFT method. Also, phenolphthalein (PP) was used for visual detection of HG complexation. Interestingly, PP undergoes a rearrangement in its structure in presence of CNW-g-β-CD because of HG complexation that turns the purple molecule into a colorless compound in alkaline condition. Addition of CNW-GA to the resulting colorless solution turned the color to purple again which easily confirmed HG formation.
A water-soluble coumarin monomer comprising quaternary ammonium ionic moiety can bind with a γ-cyclodextrin (γ-CD) macrocyclic host in a 2:1 ratio to form a homoternary complex in water. The coumarin...
The nature of mechanically interlocked molecules (MIMs) has continued to encourage researchers to design and construct a variety of high-performance materials. Introducing mechanically interlocked structures into polymers has led to novel polymeric materials, called mechanically interlocked polymers (MIPs). Rotaxane-based MIPs are an important class, where the mechanically interlocked characteristic retains a high degree of structural freedom and mobility of their components, such as the rotation and sliding motions of rotaxane units. Therefore, these MIP materials are known to possess a unique set of properties, including mechanical robustness, adaptability and responsiveness, which endow them with potential applications in many emerging fields, such as protective materials, intelligent actuators, and mechanisorption. In this review, we outline the synthetic strategies, structure-property relationships, and application explorations of various polyrotaxanes, including linear polyrotaxanes, polyrotaxane networks, and rotaxane dendrimers.
In this work, we demonstrate that liposome gels in which liposomes are connected by polyethylene glycol terminated by cholesterol groups at both ends can store hydrophilic and hydrophobic drugs in the gel interiors, inner aqueous phases, and lipid membranes. The addition of cyclodextrins (CDxs) as extrinsic stimuli led to the release of drug-entrapping liposomes due to the interactions between CDxs and cholesteryl groups and/or the alkyl chains of lipids. The addition of aqueous solutions of β-CDx, dimethyl-β-CDx, trimethyl-β-CDx, and γ-CDx (final concentration: 7.5 mM) induced the solation of liposome gels and the release of liposomes accompanying the solation. Furthermore, the addition of β-CDx led to the partial release of hydrophilic drugs encapsulated in the liposomes, although the drug release was scarcely observed in other CDxs. In particular, the addition of trimethyl-β-CDx, which has low cytotoxicity, accelerated solation, and cationic liposomes released from the gels were effectively taken up by murine colon cancer (Colon26) cells. Thus, we propose that liposomes released from liposome gels can function as drug carriers.
Les cellules dans l'organisme subissent des forces mécaniques, exercées par leur environnement, qui sont à l'origine de certains processus cellulaires. Ainsi, l'étude des relations étroites qui lient comportements cellulaires et contraintes mécaniques est aujourd'hui au cœur de la compréhension de nombreux phénomènes biologiques. Les travaux présentés dans ce manuscrit portent sur la conception et l'étude d'hydrogels photo-stimulables pouvant appliquer des contraintes sur des échantillons de tissus biologiques. Ces gels sont formés à partir de trois briques de construction, un polymère porteur d'un azobenzène tétrafluoré sensible à la lumière visible, un dérivé de ß-cyclodextrine et un polymère portant plusieurs fonctions mercapto. Ces briques sont liées par deux types de réseaux, un chimique et un physique. Le réseau chimique est formé par addition de Michael entre les thiols et les maléimides, portés par le polymère et le dérivé de cyclodextrine. Il permet au gel de posséder des propriétés mécaniques similaires à celles de l'environnement des cellules. Le réseau physique a pour rôle d'assurer le caractère photo-stimulable du matériau final par l'intermédiaire d'un complexe photo-sensible engageant l'azobenzène tétrafluoré et la ß-cyclodextrine. Le travail s'articule en trois parties. La première concerne le choix de l'azobenzène stimulable dans le visible et la caractérisation de ses propriétés et de sa complexation avec la ß-cyclodextrine, en fonction de son état d'isomérisation. La deuxième partie expose la synthèse des gels à partir des briques de construction et son optimisation, en faisant appel aux plans d'expériences. Les propriétés mécaniques de ces hydrogels et leur réponse à la lumière sont mesurées par microscopie à force atomique et par des essais de compression. La troisième partie décrit l'utilisation de ces gels en présence d'échantillons biologiques, mettant ainsi en lumière ses applications possibles en tant que support de culture cellulaire ou tissulaire. Ces travaux ont été réalisés dans le cadre du projet Gellight financé par l'Agence Nationale de la Recherche (ANR).
One of the features of syndiotactic polystyrene is its various crystalline structures according to the crystallization conditions and process. A mixture of acetylated cyclodextrin and syndiotactic polystyrene results in additional...
Self-healing materials can recover their mechanical properties after fracture. The self-healing materials can save environment and resources by expanding lifetime of the materials. Starting with the first reports on self-healing materials in the early 2000s, the era of self-healing materials has started. Supramolecular chemistry is an attractive approach to realize the self-healing properties because of its reversibility. In 2008, the first report on supramolecular self-healing materials based on hydrogen bond was reported. Up to date, numerous methodologies for supramolecular self-healing materials have been reported. This chapter mainly focuses on the self-healing supramolecular materials based on host-guest chemistry and hydrogen bonds.
Actuators, as used in materials science, can improve soft robotics. Diverse stimuli have been utilized for actuation. Among the various stimuli, light has advantages for remote and local control. Mechanical properties are important factors to consider when evaluating the practical application of such materials in soft robotics. However, simultaneous studies on mechanical and actuating properties have rarely been conducted. We focus on 6,6-Nylon and supramolecular chemistry, particularly the chemistry between γ-cyclodextrin and azobenzene, to address this issue. Movable cross-links formed by cyclodextrin and azobenzene increase the mechanical toughness of this nylon-based material. The supramolecular material exhibits reversible photoresponsiveness in terms of both mechanical and actuating properties with mechanoisomerization. With predeformation, the actuation speed and work efficiency of the supramolecular material are drastically increased upon UV irradiation. We expect that supramolecular chemistry will contribute to material innovation for soft robotics. Supramolecular nylon-based materials exhibited changes in their Young’s moduli and underwent bending upon irradiation with UV light as a result of isomerization in 1:2 complexes of γ-cyclodextrin and azobenzene. The photoisomerization of azobenzenes led to photoresponsive actuation of the supramolecular materials. The movable cross-links contributed to the mechanical toughness and photoresponsive actuation of these materials. Shape restoration of the nylon-based materials resulted in an extraordinarily high work efficiency.
The discovery of azo compounds goes back to the mid‐1800s, but recent findings show that they are switchable even in visible light. The present book chapter aims to summarize the synthetic approaches (including Mills reactions), the design concepts of different kinds of azo benzene photoswitches regarding their applications (especially in biological systems) as well as their physical properties. In the end, selected applications were given to show the overall potential of azo benzenes. Thereby, the cited literature and reviews serve as sources to be consulted for deeper understanding. Heteroaromatic azoarenes (six‐ or five‐membered ones) are compared with classical ones.
Arylhydrazones are a class of configurational photoswitches that exhibit extremely long thermal half‐lives, emission toggling, and solid‐state switching, among other properties. In this chapter, we will walk through the evolution of this novel family of photochromic compounds and highlight how their unique photoswitching properties enable new and unprecedented functions, such as the kinetic trapping of supramolecular self‐assemblies yielding multi‐state and persistent properties, and real‐time tracking of drug delivery enabled by switchable emission.
Multicharged cyclodextrin (CD) supramolecular assemblies, including those based on positively/negatively charged modified mono-6-deoxy-CDs, per-6-deoxy-CDs, and random 2,3,6-deoxy-CDs, as well as parent CDs binding positively/negatively charged guests, have been extensively applied in chemistry, materials science, medicine, biological science, catalysis, and other fields. In this review, we primarily focus on summarizing the recent advances in positively/negatively charged CDs and parent CDs encapsulating positively/negatively charged guests, especially the construction process of supramolecular assemblies and their applications. Compared with uncharged CDs, multicharged CDs display remarkably high antiviral and antibacterial activity as well as efficient protein fibrosis inhibition. Meanwhile, charged CDs can interact with oppositely charged dyes, drugs, polymers, and biomacromolecules to achieve effective encapsulation and aggregation. Consequently, multicharged CD supramolecular assemblies show great advantages in improving drug-delivery efficiency, the luminescence properties of materials, molecular recognition and imaging, and the toughness of supramolecular hydrogels, in addition to enabling the construction of multistimuli-responsive assemblies. These features are anticipated to not only promote the development of CD-based supramolecular chemistry but also contribute to the rapid exploitation of these assemblies in diverse interdisciplinary applications.
Supramolecular polymer gels (SPGs) are precisely designed gels brought together by noncovalent interactions to form three-dimensional network structures of polymers. SPGs combine the merits of supramolecular polymers and gels, such as stimuli-responsiveness, self-healing, and self-adaptation, which endows SPGs with potential application value in the fields of biomaterials, etc. Recently, much effort has been made to design new SPGs and related materials with high performance. Herein, we review the research endeavor and future directions of SPGs depending on the construction methods, topological structures, stimuli-responsiveness, and functionality. We hope that the review will provide reference values for the researchers working in supramolecular chemistry and gels.
The stimuli-responsiveness of injectable hydrogel has been drastically developed for the controlled release of drugs and achieved encouraging curative effects in a variety of diseases including wounds, cardiovascular diseases and tumors. The gelation, swelling and degradation of such hydrogels respond to endogenous biochemical factors (such as pH, reactive oxygen species, glutathione, enzymes, glucose) and/or to exogenous physical stimulations (like light, magnetism, electricity and ultrasound), thereby accurately releasing loaded drugs in response to specifically pathological status and as desired for treatment plan and thus improving therapeutic efficacy effectively. In this paper, we give a detailed introduction of recent progresses in responsive injectable hydrogels and focus on the design strategy of various stimuli-sensitivities and their resultant alteration of gel dissociation and drug liberation behaviour. Their application in disease treatment is also discussed. This article is protected by copyright. All rights reserved.
Supramolecular topological hydrogels are constructed by introducing different dynamic topological structures into polymeric networks and thus exhibit a wide variety of stimuli-responsive properties and versatile applications.
Hydrogels have been developed to respond to a wide variety of stimuli, but their use in macroscopic systems has been hindered by slow response times (diffusion being the rate-limiting factor governing the swelling process). However, there are many natural examples of chemically driven actuation that rely on short diffusion paths to produce a rapid response. It is therefore expected that scaling down hydrogel objects to the micrometre scale should greatly improve response times. At these scales, stimuli-responsive hydrogels could enhance the capabilities of microfluidic systems by allowing self-regulated flow control. Here we report the fabrication of active hydrogel components inside microchannels via direct photopatterning of a liquid phase. Our approach greatly simplifies system construction and assembly as the functional components are fabricated in situ, and the stimuli-responsive hydrogel components perform both sensing and actuation functions. We demonstrate significantly improved response times (less than 10 seconds) in hydrogel valves capable of autonomous control of local flow.
A novel coordination gelator exhibits reversible chromatic and sol-gel phase-transition phenomena triggered by thermal and chemical stimuli.
In recent years there has been immense interest in studying gels derived from low molecular mass gelators (supramolecular, or simply molecular gels). The motivation for this is not only to understand the fundamental aggregate structures in the gels at different length scales, but also to explore their potential for futuristic technological applications. Gels have been made sensitive to external stimuli like light and chemical entities by incorporating a spectroscopically active or a receptor unit as part of the gelator molecule. This makes them suitable for applications such as sensing and actuating. The diversity of gel structural architectures has allowed them to be utilized as templates to prepare novel inorganic superstructures for possible applications in catalysis and separation. Gels derived from liquid crystals (anisotropy gels) that can act as dynamically functional materials have been prepared, for example, for (re-writable) information recording. Supramolecular gels can be important in controlled release applications, in oil recovery, for gelling cryogenic fuels etc. They can also serve as media for a range of applications. This tutorial review highlights some of the instructive work done by various groups to develop smart and functional gels, and covers a wide spectrum of scientific interest ranging from medicine to materials science.
Strategies for spinal cord injury repair are limited, in part, by poor drug delivery techniques. A novel drug delivery system (DDS) is being developed in our laboratory that can provide localized release of growth factors from an injectable gel. The gel must be fast-gelling, non-cell adhesive, degradable, and biocompatible as an injectable intrathecal DDS. A gel that meets these design criteria is a blend of hyaluronan and methylcellulose (HAMC). Unlike other injectable gels, HAMC is already at the gelation point prior to injection. It is injectable due to its shear-thinning property, and its gel strength increases with temperature. In vivo rat studies show that HAMC is biocompatible within the intrathecal space for 1 month, and may provide therapeutic benefit, in terms of behavior, as measured by the Basso, Beattie and Bresnahan (BBB) locomotor scale, and inflammation. These data suggest that HAMC is a promising gel for localized delivery of therapeutic agents to the injured spinal cord.
Eine rechtsgängig‐helicale Silica‐Spirale (siehe Bild) entsteht in der Gelphase durch Sol‐Gel‐Polykondensation von Tetraethoxysilan, wobei ein Cholesterin‐Gelbildner mit einer Azakronenether‐Einheit verwendet wird. Dies ist eines der sehr seltenen Beispiele für die Bildung chiraler Strukturen in einem anorganischen Material durch die Templatmethode.
Recombinant DNA methods were used to create artificial proteins that undergo reversible gelation in response to changes in pH or temperature. The proteins consist of terminal leucine zipper domains flanking a central, flexible, water-soluble polyelectrolyte segment. Formation of coiled-coil aggregates of the terminal domains in near-neutral aqueous solutions triggers formation of a three-dimensional polymer network, with the polyelectrolyte segment retaining solvent and preventing precipitation of the chain. Dissociation of the coiled-coil aggregates through elevation of pH or temperature causes dissolution of the gel and a return to the viscous behavior that is characteristic of polymer solutions. The mild conditions under which gel formation can be controlled (near-neutral pH and near-ambient temperature) suggest that these materials have potential in bioengineering applications requiring encapsulation or controlled release of molecular and cellular species.
In this paper, we would like to present a novel system of host−guest hydrogels. By polymerizing adamantyl containing acrylamide monomers (12−15) with water soluble comonomers, we synthesized various copolymers bearing guest components. As host system we applied easily accessible β-cyclodextrin polymers with Mn values of about 30K−100K g mol−1. The viscosity of the resulting hydrogel could be influenced by the concentration of both substances, by the length of the carbon spacer chain of the guest monomer, by the pH value or by the conformation of the β-cyclodextrin polymers. Moreover, the hydrogels stayed stable in solutions of starch hydrolyzing enzyme taka-diastase from Aspergillus oryzae.
The interaction in water of α-cyclodextrin with α,Ω-dicarboxylic acids from C5 to C11 has been studied calorimetrically at 25°C in phosphate buffer at pH 11.3 and 1.3. When a complex forms, calorimetry enables the calculation of both enthalpy and association constant, from which the free energy and the entropy of the process can be obtained.At pH 11.3, 1:1 complexes are formed, the association occurring through the interaction of the charged carboxylate groups with the hydroxyl groups on the exterior of the dextrin. The alkyl chain should point toward the interior of the cavity. This ‘capping’ mechanism relies on the impossibility of the carboxylate group to reside within the cavity. At pH 1.3, the values of the association constants do not follow a regular trend with increasing alkyl chain length. Evidences are presented for a variation of the stoichiometry of association for longer chain substances. A 2:1 stoichiometry would be possible because of the ability of the uncharged carboxyl group to be included in the cavity.The forces involved in the association process are discussed in the light of the analysis of the signs and values of the thermodynamic parameters.
Alpha,omega-Alkanedicarboxylic acid anions with a long spacer methylene chain were observed to form dynamically and statically stable complexes with alpha-cyclodextrin (alpha-CD) at an NMR time scale in both neutral and basic media. The structures of these complexes were confirmed to be a ''through-ring'' type CD complex by measurements of the intermolecular NOESY and NOE difference spectra. From the thermodynamic data in basic media (pD 13), the dynamical stability of these type complexes were attributed not to the steric interaction, but to an electrostatic interaction between the dicarboxylate anion and ionized-CD.
An original associating system is presented in this paper. It involves the mixing of two polymers: hydrophobically modified polyethylene oxide (PEO) and β-cyclodextrin copolymer. Inclusion complexes between the hydrophobic moieties (naphthalene or adamantane) and β-cyclodextrin cavities are at the origin of the attraction between the two polymers. The strength of the attractive interactions has been tailored by using different architectures for the amphiphilic polymer: linear or multi-arm branched PEO have been used, leading to a variable number of hydrophobic end-groups per chain. Interactions between the host and guest polymer have been demonstrated through both microscopic and macroscopic analysis of the properties of the medium: complexation constants have been determined by fluorescence methods and dialysis, while polymolecular associations have been evidenced by viscoelastic properties. Phase diagram studies have shown that the strength of the interactions between the two polymers is strongly related to the number of hydrophobic moieties per chain: while unmodified PEO and β-cyclodextrin copolymer are phase segregating, associative phase separations are observed for a number of hydrophobes per chain higher than or equal to three.
Multiaddressable organogelators are 3,3-diphenyl-3H-naphtho[2,1-b]pyrans covalently linked to sodium N-acyl-11-aminoundecanoate. These molecules have been designed to respond to changes to their environment. They are shown to act as efficient gelators for polar organic fluids, and obviously they exhibit a thermosensitive answer as low molecular mass organogelators. In these fluids, the aggregative properties are totally suppressed upon conversion to neutral carboxylic species. The gels of these carboxylate sodium salts are shown to be markedly affected by light irradiation. Supramolecular gelating assemblies can be disrupted by the photoinduced ring opening of the chromene subunit, so that the macroscopic flowing property is recovered. Upon a further thermal treatment, the system is reversibly converted back to the supramolecular network. Controlled gelation could be achieved using temperature, light, or acidity as external stimuli.
We present a strategy to stabilize artificial protein hydrogels through covalent bond formation following physical association of terminal leucine zipper domains. Artificial proteins consisting of two terminal leucine zipper domains and a random coil central domain form transient networks above a certain concentration, but the networks dissolve when placed in excess buffer. Engineering of a cysteine residue into each leucine zipper domain allows formation of disulfide bonds templated by leucine zipper aggregation. Circular dichroism spectra show that the zipper domains remain helical after cysteine residues and disulfide bonds are introduced. Asymmetric placement of the cysteine residues in the leucine zipper domains suppresses intramolecular disulfide bonds and creates linked “multichains” composed of ca. 9 protein chains on average, as determined by multiangle light scattering measurements. These “multichains” act as the building units of the physical network formed by leucine zipper aggregation. The increased valency of the building units stabilizes the hydrogels in open solutions, while the physical nature of their association allows the reversibility of gelation to be retained. The gel networks dissolve at pH 12.2, where the helicity of the leucine zipper domains is reduced by ca. 90%, and re-form upon acidification. The hydrogels show anisotropic swelling when anchored on aminated surfaces and may find applications in tissue engineering, controlled release, and microarray technologies on the basis of their stability, reversibility, and swelling behavior.
The photocontrolled aggregation of a photosensitive azobenzene surfactant onto an oppositely charged, hydrophobically modified polyelectrolyte, that resulted in photoreversible gelation was analyzed. It was found that the aggregation concentration (cac) of the surfactant, which leds to physical cross-linking and gelation. It was observed that the visible light (trans) form of the surfactant had more hydrophobic than the UV light (ultra violet) formed. The results shows that the driving force for micellization at the cac is primarily an effect of hydrophobic interactions between surfactant tails, in contrast to electrostatic interactions between surfactant headgroup and the polymer.
Numerous two-directional cascade molecules (arborols) have been prepared via a simple two-step procedure. These cascade molecules have been abbreviated as [m]-n-[m] arborols, where m is the number of hydroxyl moieties on the cascade spherical surface and n is the number of methylenes connecting the cascade spheres. Several of the arborols in the [9]-n-[9] and [6]-n-[6] series form thermally reversible aqueous gels; properties of these gels are discussed. An aggregation model is proposed for the gel-forming molecules; preliminary molecular modeling calculations and electron micrograph data support this model.
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The construction of polymer networks through host−guest complexation between the β-cyclodextrin (βCD) substituents of 6A-(1-(2-aminoethyl)amino)-6A-deoxy-β-cyclodextrin 2, 3, and 6% randomly substituted poly(acrylate) (PAAβCDen) and the adamantyl (AD) substituents of 1-(2-aminoethyl)amidoadamantyl 2, 3, and 6% randomly substituted poly(acrylate) (PAAADen) is reported. A 2D 1H NOESY NMR spectroscopic study shows the formation of host−guest complexes by the βCD and AD substituents. This is characterized by a complexation constant, K1 = 3020 ± 60 mol−1 dm3, for 3% substituted PAAβCDen and PAAADen as shown by isothermal titration calorimetry. The viscosity of a 2 wt % equimolar mixture of 3% randomly substituted PAAβCDen and PAAADen reaches a maximum at [NaCl] = 0.1 mol dm−3, and the viscosity and the storage and loss moduli (G′ and G′′) increase with the increase in degree of substitution from 2 to 6%.
Dimeric azobenzene-appended cholesterol organogel 1 was synthesized and its gelation ability was evaluated in organic solvents. It can gelate 1-hexanol, 1-octanol, toluene, m-xylene, and p-xylene, under 5.0 wt %, indicating that 1 acts as a versatile gelator of various organic solvents. To obtain visual insights into the aggregation mode, we observed the xerogel structure of 1-octanol and m-xylene gels 1 by TEM and SEM. They revealed a typical helical fiber structure with 50−100 nm of outer diameters, suggesting that the organogel 1 grows into the bundled fiber structure in the absence of any additive. Also, we observed the CD spectrum of 1-octanol gel 1 to characterize the aggregation mode in the gel phase. In the CD spectrum, the λθ=0 value appeared at 365 nm, which is consistent with the absorption maximum at λmax = 365 nm. It is known that azobenzene-appended cholesterol gelators with natural (S) C-3 configuration tend to give a negative sign for the first Cotton effect, indicating that the dipole moments of azobenzene chromophores tend to orient in the anticlockwise direction. Sol−gel polymerization of tetraethoxysilane (TEOS) was carried out using the organogel 1 as a template. We observed the SEM pictures of the silica obtained from 1-octanol gel 1. The silica nanotube showed the fibrous structure with ca. 30-nm outer diameter and a few micrometers length. Very surprisingly, the TEM picture revealed the inner helical structure of a silica nanotube with ca. 7.5-nm inner diameter and long helical pitch, which is comparable with the width of one-dimensional molecular stacking 1 on the basis of the interdigitated van der Waals interaction between cholesterol moieties. These results indicate that the organogel 1 was successfully transcribed into the silica nanotube by the intermolecular hydrogen-bonding interaction between the amino group of the gelator and anionic silica particles.
A host polymer with pending beta-cyclodextrin side-groups and a guest polymer with pending hydrophobic 4-tert-butylanilide side groups were synthesized by polymer-analogous reactions starting from poly[(maleic anhydride)-alt-(isobutene)] ((M) over bar(w), = 60000). The inclusions of both polymers with complementary monomeric guests and hosts are proven by microcalorimetry. The interaction of the host polymer and the guest polymer in aqueous solution is accompanied by a tremendous increase in viscosity.
Eine äußerst wirksame Selbstorganisation kleiner organischer Gelbildner in verschiedenen Lösungsmitteln führt zu einem verflochtenen Netzwerk und verwandelt dabei die Flüssigkeit in ein Gel. Die neuere Entwicklung organischer Gelbildner führte u. a. zu maßgeschneiderten Gelbildnern für überkritisches CO2. Solche Stoffe kann man darüber hinaus auch als Template zum Aufbau neuartiger Materialien verwenden und als Gele, die auf einen externen Auslöser („Trigger”;) reagieren. Das Bild zeigt schematisch, wie die viskoelastischen Eigenschaften eines schaltbaren organischen Gels beeinflusst werden können.
Eine nichtkovalente Vernetzung Adamantylgruppen tragender Copolymere von N-Isopropylacrylamid gelingt mit Cyclodextrin-Dimeren (siehe Bild). Hierdurch kommt es zur Bildung thermosensitiver Hydrogele, deren Trübungspunkte niedriger als die der unvernetzten Copolymere liegen. Bei Zugabe von monomerem methyliertem Cyclodextrin zu Lösungen der reinen Copolymere steigen die Trübungspunkte; dies hat jedoch kaum Einfluss auf die Viskosität der Polymerlösungen.
Die Wissenschaft wird wie die Kunst und Architektur von den faszinierenden Formen und Mustern der Natur beeinflusst. Die Mechanismen, die zu organischen, anorganischen und bioorganischen Strukturen führen, wurden in der Physik und Biologie intensiv erforscht, aber auch die Chemie interessiert sich für die Konzepte, auf denen die Bildung regelmäßiger Formen beruht. Während in der Organischen und insbesondere der Supramolekularen Chemie die Synthese großer Überstrukturen bereits früh mit großem Erfolg umgesetzt wurde, gelang es innerhalb der Anorganischen Chemie erst in den letzten Jahren, Verfahren zur Steuerung der Struktur anorganischer Materialien auf mikroskopischer und nanoskopischer Ebene zu entwickeln. Einer der erfolgreichsten Ansätze zur Herstellung anorganischen Strukturen beruht dabei auf der Verwendung organischer und bioorganischer Template, einer Methode, deren Leistungsfähigkeit in diesem Aufsatz vorgestellt werden soll.
By IR and NMR spectroscopy methods, thermomechanical analysis, mechanical relaxation measurements, and computational simulation the effect of production conditions of acrylamide copolymer and N,N′-methylenebisacrylamide derived hydrogels with respect to their properties were studied. Four hydrogel samples, prepared under different production conditions (γ-radiation dose and autoclaving), were investigated. It was found that autoclaving and γ-radiation lead to a slight increase of the crosslinking degree in the polymeric network and formation of alkene structures in polymeric chains. Stress relaxation and creep processes under axial compression of gel cylindrical samples were studied in detail. To approximate stress relaxation and creep curves new memory functions were used, based on the analysis of entropy production in the system during the relaxation process. It was found that primary γ-radiation of initial gels induces an increase of quasi-equilibrium rubbery elasticity modulus, and quasi-equilibrium compliance is decreased. The opposite situation is observed during further autoclaving at 120°C. After autoclaving, required to sterilize the gels, their treatment by γ-radiation again induced a noticeable increase of the modulus and compliance decrease. The mechanism of relaxation processes was found to be associated with the limiting stage of physical interaction between relaxants, representing different micro-inhomogeneities in the material. The investigation results were compared with the data obtained by histology and morphology methods. A hydrogel obtained under additional γ-radiation treatment and autoclaving did not swell when implanted into a living organism, and the tissue reaction to implantation of such gel was minimal. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1043–1058, 2005
Original associating systems have been obtained by mixing hydrophobically end-capped polyethylene oxide and water soluble -cyclodextrin polymers in aqueous solutions. The hydrophobic ends of the PEO polymers, naphtyl and adamantyl groups, have been chosen in order to match the -cyclodextrin cavities. Inclusion complex formation between the PEO terminal groups and -cyclodextrin are at the origin of polymolecular associations. Complexation constants have been determined by fluorescence methods, using a fluorescent probe 1-8 ANS as a competitor for complexation against the adamantyl groups or directly checking the fluorescence of the naphtytl groups by fluorescence anisotropy measurements. The onsets of the polymolecular associations have been monitored by viscosimetry.
Long-term, localized delivery of growth factors may help regenerate lost structure and function in diseased or traumatized tissues. In previous reports, we have described techniques for releasing precisely controlled quantities of mouse nerve growth factor (NGF) from a poly (ethylene-co-vinyl acetate) matrix. To further study the dynamics and bioactivity of NGF released from a polymer matrix, we cultured PC 12 cells within hydrated gels of type I collagen and embedded a polymer matrix containing NGF in one end of the gel. Spatial variations in neurite outgrowth and NGF concentration were determined for 2 weeks. For comparison, the rate of NGF release from the polymer matrix into buffered saline was also determined. NGF released from a biocompatible polymer matrix induced neurite outgrowth in cells cultured within a three-dimensional gel of collagen. NGF was transported through the collagen gel by diffusion through the gel and convection due to fluid movement into the overlying, well-mixed fluid layer. The extent of neurite outgrowth from the cell clumps at any position in the gel depended on both the time following polymer insertion and distance from the polymer. Neurite outgrowth was most dense within the 15-mm region nearest the polymer, although biologically active NGF did penetrate as far as 38 mm. These techniques may be useful in evaluating the role of controlled release polymers in growth factor delivery to tissues. In addition, this experimental system can be used to quantify the response of tissue-derived cells to well-defined gradients of biologically active factors.
An original associating system is presented in this paper. It involves the mixing of two polymers: hydrophobically modified polyethylene oxide (PEO) and β-cyclodextrin copolymer. Inclusion complexes between the hydrophobic moieties (naphthalene or adamantane) and β-cyclodextrin cavities are at the origin of the attraction between the two polymers. The strength of the attractive interactions has been tailored by using different architectures for the amphiphilic polymer: linear or multi-arm branched PEO have been used, leading to a variable number of hydrophobic end-groups per chain. Interactions between the host and guest polymer have been demonstrated through both microscopic and macroscopic analysis of the properties of the medium: complexation constants have been determined by fluorescence methods and dialysis, while polymolecular associations have been evidenced by viscoelastic properties. Phase diagram studies have shown that the strength of the interactions between the two polymers is strongly related to the number of hydrophobic moieties per chain: while unmodified PEO and β-cyclodextrin copolymer are phase segregating, associative phase separations are observed for a number of hydrophobes per chain higher than or equal to three.
Surface-patterned 2-hydroxyethyl methacrylate hydrogels were produced by using a method similar to the silicon-rubber stamp fabrication for microcontact printing. Polymerization and network formation were carried out in contact with a micromachined silicon wafer. The polymeric patterns retained their shape during isotropic swelling/deswelling cycles. The use of microstructured hydrogels in tissue engineering can be envisaged.
A close correllation between molecular‐level interactions and macroscopic characteristics of polymer networks exists. The characteristics of the polymeric hydrogels assembled from β‐cyclodextrin (β‐CD) and adamantyl (AD) substituted poly(acrylate)s can be tailored through selective host–guest complexation between β‐CD and AD substituents and their tethers. Dominantly, steric effects and competitive intra‐ and intermolecular host–guest complexation are found to control poly(acrylate) isomeric inter‐strand linkage in polymer network formation. This understanding of the factors involved in polymeric hydrogel formation points the way towards the construction of increasingly sophisticated biocompatible materials.
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A novel self-assembling poly(ethylene glycol) hydrogel system based on inclusion complexes between β-cyclodextrin (β-CD) and cholesterol is described. Hydrogels are formed after hydration of a mixture of star-shaped 8-arm poly(ethylene glycol) (PEG) end-modified with β-CD groups and the same star-shaped PEG end-modified with cholesterol moieties. Rheological analysis as well as 2D-NMR spectroscopy demonstrated that the obtained gels are due to formation of β-CD/cholesterol inclusion complexes. As also observed by rheology, the hydrogels are fully thermoreversible upon repetitive heating and cooling steps. Hydrogel properties were dependent on polymer concentration, the β-CD/cholesterol stoichiometry, and the molecular weight of the star-shaped PEG. Because of their assumed biocompatibility and expected physiological clearance, hydrogels based on star-shaped PEG and β-CD/cholesterol inclusion complexes offer excellent opportunities as drug delivery matrices and for other pharmaceutical and biomedical applications.
A SYSTEM capable of converting chemical energy to mechanical energy could serve as an actuator or an 'artificial muscle' in several applications. Here we describe a chemomechanical system of this sort based on a synthetic polymer gel. The gel network is anionic, and positively charged surfactant molecules can therefore bind to its surface, inducing local shrinkage by decreasing the difference in osmotic pressure between the gel interior and the solution outside. By using an electric field to direct surfactant binding selectively to one side of the gel, we can induce contraction and curvature of a strip of gel. Reversing the direction of the field causes contraction of the opposite side, and when the gel is suspended in solution from a ratchet mechanism, it can thereby be made to move with a worm-like motion at a velocity of up to 25 cm min-1.
The last two decades have witnessed an upsurge of research activities in the area of supramolecular gelators, especially low molecular mass organic gelators (LMOGs), not only for academic interests but also for their potential applications in materials science. However, most of the gelators are serendipitously obtained; their rational design and synthesis is still a major challenge. Wide structural diversities of the molecules known to act as LMOGs and a dearth of molecular level understanding of gelation mechanisms make it difficult to pin-point a particular strategy to achieve rational design of gelators. Nevertheless, some efforts are being made to achieve this goal. Once a gelling agent is serendipitously obtained, new gelling agents with novel properties may be prepared by modifying the parent gelator molecule following a molecular engineering rationale; however, such approach is limited to the same class of gelling agent generated from the parent gelating scaffold. A crystal engineering approach wherein the single-crystal structure of a molecule is correlated with its gelling/nongelling behaviour (structure-property correlation) allows molecular level understandings of the self-assembly of the gelator and nongelator molecules and therefore, provides new insights into the design aspects of supramolecular gelling agents. This tutorial review aims at highlighting some of the developments covering both molecular and crystal engineering approaches in designing LMOGs.
A right-handed helical motif is shown by the spiral silica shown in the picture. It is formed by sol-gel polycondensation of tetraethoxysilane in the gel phase supported by an azacrown-appended cholesterol gelator. This is rare example of 'chirality' being created in the inorganic material by the template method.
Hydrogels are presently under investigation as matrices for the controlled release of bioactive molecules, in particular pharmaceutical proteins, and for the encapsulation of living cells. For these applications, it is often required that the gels degrade under physiological conditions. This means that the originally three-dimensional structure has to disintegrate preferably in harmless products to ensure a good biocompatibility of the hydrogel. In this overview, different chemical and physical crosslinking methods used for the design of biodegradable hydrogels are summarized and discussed. Chemical crosslinking is a highly versatile method to create hydrogels with good mechanical stability. However, the crosslinking agents used are often toxic compounds, which have been extracted from the gels before they can be applied. Moreover, crosslinking agents can give unwanted reactions with the bioactive substances present in the hydrogel matrix. Such adverse effects are avoided with the use of physically crosslinked gels.
Synthetic polymers offer a wealth of opportunities to design responsive materials triggered by external stimuli. Changing
the length, chemical composition, architecture, and topology of the chains allows response mechanisms and rates to be easily
manipulated; and devices based on the entropy of the chains, surface energies, and specific segmental interactions can readily
be made. Although numerous applications exist, intriguing possibilities are emerging that have tremendous potential to further
developments in surface-responsive materials.
We report the design of surfaces that exhibit dynamic changes in interfacial properties, such as wettability, in response to an electrical potential. The change in wetting behavior was caused by surface-confined, single-layered molecules undergoing conformational transitions between a hydrophilic and a moderately hydrophobic state. Reversible conformational transitions were confirmed at a molecular level with the use of sum-frequency generation spectroscopy and at a macroscopic level with the use of contact angle measurements. This type of surface design enables amplification of molecular-level conformational transitions to macroscopic changes in surface properties without altering the chemical identity of the surface. Such reversibly switching surfaces may open previously unknown opportunities in interfacial engineering.
Mankind's fascination with shapes and patterns, many examples of which come from nature, has greatly influenced areas such as art and architecture. Science too has long since been interested in the origin of shapes and structures found in nature. Whereas organic chemistry in general, and supramolecular chemistry especially, has been very successful in creating large superstructures of often stunning morphology, inorganic chemistry has lagged behind. Over the last decade, however, researchers in various fields of chemistry have been studying novel methods through which the shape of inorganic materials can be controlled at the micro- or even nanoscopic level. A method that has proven very successful is the formation of inorganic structures under the influence of (bio)organic templates, which has resulted in the generation of a large variety of structured inorganic structures that are currently unattainable through any other method.
Hydrogels composed of N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc) were prepared by redox polymerization with peptide cross-linkers to create an artificial extracellular matrix (ECM) amenable for testing hypotheses regarding cell proliferation and migration in three dimensions. Peptide degradable cross-linkers were synthesized by the acrylation of the amine groups of glutamine and lysine residues within peptide sequences potentially cleavable by matrix metalloproteinases synthesized by mammalian cells (e.g., osteoblasts). With the peptide cross-linker, loosely cross-linked poly(N-isopropylacrylamide-co-acrylic acid) [P(NIPAAm-co-AAc)] hydrogels were prepared, and their phase transition behavior, lower critical solution temperature (LCST), water content, and enzymatic degradation properties were investigated. The peptide-cross-linked P(NIPAAm-co-AAc) hydrogels were pliable and fluidlike at room temperature and could be injected through a small-diameter aperture. The LCST of peptide-cross-linked hydrogel was influenced by the monomer ratio of NIPAAm/AAc but not by cross-linking density within the polymer network. A peptide-cross-linked hydrogel with a 97/3 molar ratio of NIPAAm/AAc exhibited a LCST of approximately 34.5 degrees C. Swelling was influenced by NIPAAm/AAc monomer ratio, cross-linking density, and swelling media; however, all hydrogels maintained more than 90% water even at 37 degrees C. In enzymatic degradation studies, breakdown of the peptide-cross-linked P(NIPAAm-co-AAc) hydrogels was dependent on both the concentration of collagenase and the cross-linking density. These results suggest that peptide-cross-linked P(NIPAAm-co-AAc) hydrogels can be tailored to create environmentally-responsive artificial extracellular matrixes that are degraded by proteases.
We describe the development of an injectable, cell-containing hydrogel that supports cell proliferation and growth to permit in vivo engineering of new tissues. Two thiolated hyaluronan (HA) derivatives were coupled to four alpha,beta-unsaturated ester and amide derivatives of poly(ethylene glycol) (PEG) 3400. The relative chemical reactivity with cysteine decreased in the order PEG-diacrylate (PEGDA)>PEG-dimethacrylate>PEG-diacrylamide>PEG-dimethacrylamide. The 3-thiopropanoyl hydrazide derivative (HA-DTPH) was more reactive than the 4-thiobutanoyl hydrazide, HA-DTBH. The crosslinking of HA-DTPH with PEGDA in a molar ratio of 2:1 occurred in approximately 9 min, suitable for an in situ crosslinking applications. The in vitro cytocompatibility and in vivo biocompatibility were evaluated using T31 human tracheal scar fibroblasts, which were suspended in medium in HA-DTPH prior to addition of the PEGDA solution. The majority of cells survived crosslinking and the cell density increased tenfold during the 4-week culture period in vitro. Cell-loaded hydrogels were also implanted subcutaneously in the flanks of nude mice, and after immunohistochemistry showed that the encapsulated cells retained the fibroblast phenotype and secreted extracellular matrix in vivo. These results confirm the potential utility of the HA-DTPH-PEGDA hydrogel as an in situ crosslinkable, injectable material for tissue engineering.
We describe a method for repetitive and rapid formation of planar microarrays and gradients of proteins using patterned agarose stamps. It demonstrates: (i) micropatterning of agarose gels with feature sizes as small as 2 microm; (ii) inking of posts (diameter 50-1000 microm) on patterned agarose stamps with one or multiple (here, eight) proteins and repetitive stamping of patterns (>100 times in the case of one protein) and arrays (20 times in the case of eight proteins) without the need for intermediate re-inking; (iii) transferring spots of proteins with good homogeneity in surface coverage to glass slides; (iv) applying this technique to surface-based immunoassays; (v) stamping that requires only sub-nanomolar amounts of protein (typically approximately 3 microg in approximately 0.6 microL of solution); (vi) stamping without the need for drying of the proteins, as opposed to stamping with stamps made of poly(dimethylsiloxane); and (vii) patterning gradients of proteins by allowing two proteins to diffuse toward each other in an agarose stamp, followed by printing the protein gradients onto a surface.
Materials are said to show a shape-memory effect if they can be deformed and fixed into a temporary shape, and recover their original, permanent shape only on exposure to an external stimulus. Shape-memory polymers have received increasing attention because of their scientific and technological significance. In principle, a thermally induced shape-memory effect can be activated by an increase in temperature (also obtained by heating on exposure to an electrical current or light illumination). Several papers have described light-induced changes in the shape of polymers and gels, such as contraction, bending or volume changes. Here we report that polymers containing cinnamic groups can be deformed and fixed into pre-determined shapes--such as (but not exclusively) elongated films and tubes, arches or spirals--by ultraviolet light illumination. These new shapes are stable for long time periods, even when heated to 50 degrees C, and they can recover their original shape at ambient temperatures when exposed to ultraviolet light of a different wavelength. The ability of polymers to form different pre-determined temporary shapes and subsequently recover their original shape at ambient temperatures by remote light activation could lead to a variety of potential medical and other applications.
Graft survival and integration are major factors that limit the efficacy of cell therapies for the treatment of disease and injury in the central nervous system. Efforts to improve cell survival and integration have focused in part on the development of biocompatible scaffolds that support neural cell growth and function. Here we photoencapsulate neural cells within degradable hydrogels and use confocal microscopy to non-invasively monitor these key cell functions over time. By directly imaging fluorescently labeled cells we show that neural cells cultured within three-dimensional polymer networks create their own cellular microenvironment to survive, proliferate and differentiate and form neurons and glia that are electrophysiologically responsive to neurotransmitter. By changing the degradation rate of the polymer network, the time-scale over which neural cells extend processes throughout the hydrogel could be tuned on a time-scale that ranged from 1-3 weeks. These studies were carried out in the absence of serum and extracellular matrix molecules that can be immunogenic and identify degradable PEG hydrogels as suitable synthetic cell carriers for neural transplantation.
Polymer-polymer interactions were investigated for mixtures of a poly(acrylic acid) (pAA) carrying azobenzene (pC12Azo) and two kinds of pAA carrying alpha-cyclodextrin (CD), in which CDs are attached to the main chain through the 3- and 6-positions in CD (p3alphaCD and p6alphaCD, respectively), using several techniques, such as viscosity and NMR measurements. Viscosity data exhibited contrast changes upon UV irradiation: thinning (p3alphaCD/pC12Azo) and thickening (p6alphaCD/pC12Azo). NOESY spectra confirmed that the contrast viscosity changes were ascribable to differences in how CD moieties interact with pC12Azo after photoisomerization of azobenzene moieties from trans to cis: dissociation of inclusion complexes (p3alphaCD/pC12Azo) and formation of interlocked complexes (p6alphaCD/pC12Azo).
En route to intelligent hydrogels: Copolymers of N-isopropylacrylamide containing adamantyl groups can be cross-linked noncovalently with cyclodextrin dimers. This results in thermosensitive hydrogels with cloud points that are lower than those of the pure copolymers. Addition of monomeric methylated cyclodextrin results in an increase in the cloud points but has no significant influence on the viscosity of the copolymer solution. (Figure Presented)
Interactions in semidilute solutions of a hydrophobically modified alginate (HM-alginate) in the presence of hydroxypropyl-beta-cyclodextrin (HP-beta-CD) monomer or a beta-cyclodextrin polymer (poly(beta-CD)) have been characterized at different temperatures with the aid of rheology and small-angle neutron scattering (SANS). The viscosity results for the HM-alginate/HP-beta-CD system reveal progressive deactivation of the hydrophobic associations as the concentration of HP-beta-CD increases. For the HM-alginate/poly(beta-CD) system, on the other hand, addition of poly(beta-CD) sets up bridges between adjacent polymer chains and thereby strengthens the associative network. A novel shear-thickening effect is observed at fairly high shear rates for the HM-alginate/poly(beta-CD) system, and this feature is influenced by temperature. Elevated temperature induces higher chain mobility and the formation of weaker network associations. Analyses of the SANS data disclosed that the association strength in HM-alginate/poly(beta-CD) mixtures increases strongly with increasing cosolute concentration, whereas no effect or a moderate weakening of the strength can be traced in HM-alginate/HP-beta-CD solutions upon addition of HP-beta-CD. The value of the correlation length xi is virtually not affected by the addition of cosolute for the HM-alginate/poly(beta-CD) system, whereas the decoupling of hydrophobic moieties of the polymer upon addition of HP-beta-CD gives rise to a smaller value of xi, suggesting that the size of the heterogeneity patches is reduced. The SANS results suggest that compact association structures are formed in the HM-alginate/poly(beta-CD) solutions.
Einfache Komponenten sind die Bausteine des beschriebenen Seitenketten-Polyrotaxans, dessen Einschlussverhalten über die Photoisomerisierung einer Azobenzol-Einheit am Ende der Seitenkette gesteuert wird.
Photoresponsive C3-symmetrical trisurea self-assembling building blocks containing three azobenzene groups (LC10 and LC4) at the rim were designed and synthesized. By introducing a trisamide gelator (G18), which can self-aggregate through hydrogen bonds of acylamino moieties to form a fibrous network, the mixture of LC10 (or LC4) and G18 forms an organogel with coral-like supramolecular structure from 1,4-dioxane. The cooperation of hydrogen bonding and the hydrophobic diversity between these components are the main contributions to the specific superstructure. The two-component gel exhibits reversible photoisomerization from trans to cis transition without breakage of the gel state.
Sol-gel processing is well-known to be a powerful technique for designing materials for optical applications. Here, some recent applications of functionalized sol-gel coatings in optics are briefly reviewed. Lanthanide-doped oxide nanocrystals form a new promising class of nanophosphors allowing the easy sol-gel preparation of transparent and luminescent films for the development of light-emitting devices. Recent experiments on organized mesoporous films show their potential applications in optics, such as stable low-index layers in interferential antireflective devices or as silica binders in TiO 2-photocatalytic devices.
In aqueous solutions, beta-cyclodextrin (CD) and cyclodextrin-containing polymers (PolCD) associate with azobenzene-modified polyacrylate (AMP). Inclusion complexes in solution of CD (or PolCD) and AMP, and the viscosity of these mixtures, have been studied as a function of the composition of AMP and concentrations of samples. AMPs are random copolymers containing a low fraction of a light-responsive hydrophobic moieties (<10 mol % of 6-[4-alkylamido]phenylazobenzene acrylamide), and a charged hydrophilic unit, sodium acrylate. PolCDs are beta-cyclodextrin randomly conjugated with epichlorohydrin and fractionated to yield copolymers of average number of CD per chain equal to 50. In dilute solutions, the composition of complexes has been investigated by capillary electrophoresis and UV-vis spectrometry. Association between PolCD and AMP appears more complex than the conventional Benesi-Hildebrand scheme. We identified a tight (quantitative) binding regime followed by a gradual increase of the density of AMP-bound PolCD upon increasing the concentration of PolCD. At higher concentrations, the formation of large clusters has been characterized by the increase of viscosity by several decades. Light-triggered trans-conformation of the azobenzene moieties of AMPs leads to a marked photoswitch of viscosity. Reversible viscosity swings by up to 6-fold were achieved by alternative exposure to UV and visible lights. In contrast, the composition of PolCD/AMP complexes in dilute regime does not respond to light, though subtle modifications of the structures of complexes are reflected by variation of electrophoretic mobilities and UV spectra. The properties of interpolymer clusters and photoviscosity are accordingly the result of modification of the dynamics of association. In practice, the low concentration of photochrome makes it possible to obtain rapid responses in samples having a thickness of the order of cm. The data reported provide guidelines for the formulations of CD/polymer systems, specifically, viscosity enhancers, which should show promising developments in pharmaceuticals or cosmetics.