Synthesis and applications of stimuli-responsive hyperbranched polymers

Benefiting from their responsiveness and adaptability, the stimuli-responsive polymers have been widely investigated and exploited in the various fields, such as environmental monitoring, electronics, photonics, controlled drug delivery, medical imaging and diagnostics. These potential applications have greatly promoted the development of advanced functional materials, and meanwhile set higher requirements for the smart materials in the aspects of the spatial structures, diverse linkages and variable functions. However, the linear functional polymers can not satisfy all the requirements of the multi-dimensional molecular design and acute sensitiveness due to the architectural limitation. Accordingly, stimuli-responsive hyperbranched polymers (HBPs) have been drawing more and more attention in recent years owing to their unique globular void-containing topological structure featured with a large number of terminal functional groups and branches, lower solution or melt viscosity, and better solubility. Therefore, design and synthesis of stimuli-responsive HBPs provide a robust tool for controlling the structure transition and creating the hierarchical sensitivity driven by different triggers. In this review, the developments and recent advances of preparation procedures, performance control and promising applications of various stimuli-responsive HBPs have been comprehensively summarized. Besides, the developing trend of stimuli-responsive HBPs is also discussed. It can be found that stimuli-responsive HBPs with different synthetic strategies and diverse performances have manifested more and more versatile applications.     

Responsive nanostructures from aqueous assembly of rigid-flexible block molecules

During the past decade, supramolecular nanostructures produced via self-assembly processes have received considerable attention because these structures can lead to dynamic materials. Among these diverse self-assembly systems, the aqueous assemblies that result from the sophisticated design of molecular building blocks offer many potential applications for producing biocompatible materials that can be used for tissue regeneration, drug delivery, and ion channel regulation. Along this line, researchers have synthesized self-assembling molecules based on ethylene oxide chains and peptide building blocks to exploit water-soluble supramolecular structures. Another important issue in the development of systems that self-assemble is the introduction of stimuli-responsive functions into the nanostructures. Recently, major efforts have been undertaken to develop responsive nanostructures that respond to applied stimuli and dynamically undergo defined changes, thereby producing switchable properties. As a result, this introduction of stimuli-responsive functions into aqueous self-assembly provides an attractive approach for the creation of novel nanomaterials that are capable of responding to environmental changes. This Account describes recent work in our group to develop responsive nanostructures via the self-assembly of small block molecules based on rigid-flexible building blocks in aqueous solution. Because the rigid-flexible molecules self-assemble into nanoscale aggregates through subtle anisometric interactions, the small variations in local environments trigger rapid transformation of the equilibrium features. First, we briefly describe the general self-assembly of the rod amphiphiles based on a rigid-flexible molecular architecture in aqueous solution. We then highlight the structural changes and the optical/macroscopic switching that occurs in the aqueous assemblies in response to the external signals. For example, the aqueous nanofibers formed through the self-assembly of the rod amphiphiles respond to external triggers by changing their shape into nanostructures such as hollow capsules, planar sheets, helical coils, and 3D networks. When an external trigger is applied, supramolecular rings laterally associate and merge to form 2D networks and porous capsules with gated lateral pores. We expect that the combination of self-assembly principles and responsive properties will lead to a new class of responsive nanomaterials with many applications.     

Towards hierarchically ordered functional porous polymeric surfaces prepared by the breath figures approach

This article reviews the approaches developed to prepare and characterize porous structured materials by using the breath figures (BF) methodology. In particular, we have analyzed the topographical modifications of the surface that can be tuned with this approach, such as the control of the pore characteristics, changes in the pore morphology or use of non-planar substrates to create the porous materials among others. We have also given special attention to the functionality inside of the pores and how this can be created by using different kinds of polymers, from homopolymers to hybrid materials, as well as by changing the pore functionally after chemical modification. The approaches followed to obtain hierarchical structures, for example, by combination of the BF approach and nanostructure formation within the pores or by using soft-lithography have also been examined. In addition, we discuss the feasibility of obtaining stimuli-responsive honeycomb structured surfaces. The potential applications in different areas such as biomedicine, optics and so on, are also pointed out. Finally, we comment on some future perspectives of breath figures approach.     

Programmed morphing of liquid crystal networks

A promising candidate for the development of stimuli-responsive morphing materials are based on liquid crystal polymer networks. These anisotropic materials will contract along the alignment director and expand perpendicular to it when subjected to an anisotropy-reducing stimulus, such as heat. As the liquid crystals can be aligned prior to polymerization using various alignment techniques, it is possible to create networks with programmed, complex director profiles in three dimensions. This review shows the various designs that can be implemented and the complex morphing behavior that can be achieved in liquid crystal polymer networks.     

Combining Chemistry,Materials Science,Inspiration from Nature,and Serendipity to Develop Stimuli-Responsive Polymeric Materials

Neither of us can remember people talking about stimuli-responsive polymers when we were students. Even though this was still in the last century, it was almost 70 years after Staudinger's seminal paper “Über Polymerisation”!^[1] By the time we entered graduate school in the early 1990 s, the first papers on polymer light emitting diodes appeared, while research on electrically conducting, nonlinear optical, and other “functional” polymers was already in full swing. Looking back, there were some stimuli-responsive materials that were around at the time,^[2–6] but it took the better part of the last 30 years until the field had developed into what we think is one of the most vibrant areas of polymer science.^[8–12] Before the potential usefulness of this class of materials was recognized, researchers were focused on developing polymeric materials that would not respond to external influences, and in fact maintain (in particular) their mechanical properties in a wide range of environments. This has led to the development of many environmentally robust polymers, which have come to impact basically every aspect of our daily life. Ironically, this long-sought stability now comes back to haunt us in the form of plastic pollution, but this is another story. The concept of materials that adapt their properties in response to changing environmental conditions might appear like a complete reversal with respect to the original goals of creating stable materials. However, eventually a) it was recognized that materials that respond to a specific stimulus in a predictable and useful manner would significantly broaden the potential usefulness of polymers, and b) the field of polymer science had developed to the point where the rational design, preparation, and characterization of such materials became possible. The expression ‘stimuli-responsive polymer’ had been first used in the 1980’s, however its use really only gained popularity a few decades later. In the early days, terms such as environmentally-sensitive or environmentally-responsive polymers, stimuli-reversible or stimuli-sensitive polymers, or polymers with phase transitions have also been used.     

Review on Technological Significance of Photoactive,Electroactive, pH-sensitive,Water-active,and Thermoresponsive Polyurethane Materials

This feature article presents a state-of-the-art review on versatile shape memory polymer, i.e., polyurethane. It forms an important class of shape memory polymers. Several successful stimuli-responsive effects have been achieved in polyurethane such as electroactive, water-active, pH-sensitive, thermoresponsive, and photoactive effect. Various categories of stimuli-responsive polyurethanes are discussed here. Due to characteristic attributes, such as light weight, low cost, high strength, heat stability, fine shape deformability, and shape memory, polyurethane have found application in aerospace, textile industry, sensors, drug delivery systems, and other biomedical relevance. Future advancement is still needed in this field due to structural and industrial preferences.     

Supplementary cementing materials in concrete: Part II: A fundamental estimation of the efficiency factor

For comparing the relative performance of various supplementary cementing materials (SCMs: silica fume, fly ash, slag, natural pozzolans, etc.) as regards Portland cement, the practical concept of an efficiency factor may be applied. The efficiency factor (or k value) is defined as the part of the SCM in an SCM-concrete that can be considered as equivalent to Portland cement. In the present work, an alternative procedure for experimental determination of the k value is proposed, using the concept of the pozzolanic activity index. For the first time, also, the k value for equivalent strength was correlated with the active silica content of the SCM through analytical expressions. Artificial pozzolanic materials of various compositions and some natural pozzolans were studied. It was found and verified by experimental comparison that these expressions are valid only for artificial SCMs (fly ash, slag), whereas in the case of natural SCMs the k value is overestimated. Thus, knowing primarily the active silica content of the SCM, a first approximation of the k value can be obtained and, further, the strength of a concrete incorporating artificial SCM can be predicted.     

刺激响应性聚合物的设计、合成及其应用研究新进展

介绍了研究刺激响应性聚合物的意义,针对水体系中的刺激响应性聚合物,介绍了近年来刺激响应性聚合物的设计与合成中的应用研究新进展,主要从3个方面进行阐述:①单一刺激响应性聚合物,包括温度、pH值、光、其他刺激响应性聚合物;②双重刺激响应性聚合物,包括温度-pH值、温度-光、温度-氧化还原刺激响应聚合物、pH值-氧化还原刺激响应聚合物;③多重刺激响应性聚合物,包括温度-光-pH值、温度-光-氧化还原、温度-pH值-CO₂刺激响应聚合物。着重评述了水体系中双重和多重刺激响应性聚合物的合成研究及应用。最后总结了多重刺激响应性聚合物应用研究的现状及问题,指出开发刺激响应性高度可控、灵敏度高、可逆性好的新型多重刺激响应性聚合物是未来的研究方向。     

Mechanical Assembly of Thermo‐Responsive Polymer‐Based Untethered Shape‐Morphing Structures

Shape‐morphing robotic structures can provide innovative approaches for various applications ranging from soft robotics to flexible electronics. However, the programmed deformation of direct‐3D printed polymer‐based structures cannot be separated from their subsequent conventional shape‐programming process. This work aims to simplify the fabrication process and demonstrates a rapid and adaptable approach for building stimulus‐responsive polymer‐based shape‐morphing structures of any shape. This is accomplished through mechanically assembling a set of identical self‐bending units in different patterns to form morphing structures using auxiliary hard connectors. A self‐bending unit fabricated by a 3D printing method can be actuated upon heating without the need for tethered power sources and is able to transform from a flat shape to a bending shape. This enables the assembled morphing‐structure to achieve the programmed integral shape without the need for a shape‐programming process. Differently assembled morphing structures used as independent robotic mechanisms are sequentially demonstrated with applications in biomimetic morphing structures, grasping mechanisms, and responsive electrical devices. This proposed approach based on a mechanical assembling method paves the way for rapid and simple prototyping of stimulus‐responsive polymer‐based shape‐morphing structures with arbitrary architectures for a variety of applications in deployable structures, bionic mechanisms, robotics, and flexible electronics.     

Active Polymer Gel Actuators

Many kinds of stimuli-responsive polymer and gels have been developed and applied to biomimetic actuators or artificial muscles. Electroactive polymers that change shape when stimulated electrically seem to be particularly promising. In all cases, however, the mechanical motion is driven by external stimuli, for example, reversing the direction of electric field. On the other hand, many living organisms can generate an autonomous motion without external driving stimuli like self-beating of heart muscles. Here we show a novel biomimetic gel actuator that can walk spontaneously with a worm-like motion without switching of external stimuli. The self-oscillating motion is produced by dissipating chemical energy of oscillating reaction. Although the gel is completely composed of synthetic polymer, it shows autonomous motion as if it were alive.     

Photolithographically patterned smart hydrogel based bilayer actuators

We describe the fabrication of photopatterned actuators, composed of stimuli-responsive hydrogel bilayers made from N-isopropyl-acrylamide (NIPAm), acrylic acid (AAc), and poly-ethylene oxide diacrylate (PEODA). The hydrogels were deposited by spin coating and casting and were patterned by non-contact photolithography. We investigated the swelling behavior of the individual photopatterned hydrogels in aqueous solutions of varying pH and ionic strength (IS). By combining materials with optimal swelling responses, bilayer structures were triggered via changes in pH and IS to actuate into three dimensional (3D) structures. We also used these hydrogel bilayers as hinges to actuate integrated structures composed of rigid polymeric SU-8 panels, patterned to resemble the shape of a Venus Flytrap. This system provides a straightforward way to design and fabricate actuator hinges composed entirely of polymers.     

Recent Advances of DNA Tetrahedra for Therapeutic Delivery and Biosensing

The chemical and self-assembly properties of nucleic acids make them ideal for the construction of discrete structures and stimuli-responsive devices for a diverse array of applications. Amongst the various three-dimensional assemblies, DNA tetrahedra are of particular interest, as these structures have been shown to be readily taken up by the cell, by the process of caveolin-mediated endocytosis, without the need for transfection agents. Moreover, these structures can be readily modified with a diverse range of pendant groups to confer greater functionality. This minireview highlights recent advances related to applications of this interesting DNA structure including the delivery of therapeutic agents ranging from small molecules to oligonucleotides in addition to its use for sensing and imaging various species within the cell.     

双重刺激响应型pickering乳液研究进展

Pickering乳液因其极强的稳定性、良好的生物相容性和对环境友好等特点在众多领域有着广泛应用.虽然乳液必须具有良好的稳定性,但实际应用中通过适当的触发机制使其能够实现快速破乳也是非常重要的.响应型Pickering乳液由于在特定因素刺激下可以轻易实现可逆乳化-破乳成为近些年研究的热点.早期研究学者主要研究单一刺激因...     

Conversion of wooden structures into porous SiC with shape memory synthesis

Synthesis of structured silicon carbide materials can be accomplished using wooden materials as the carbon source, with various silicon impregnation techniques. We have explored the low cost synthesis of SiC by impregnation of carbon from wood with SiO gas at high temperatures, which largely retains the structure of the starting wood (shape memory synthesis). Suitably structured, porous SiC could prove to be an important type of catalyst support material. Shape memory synthesis (SMS) has earlier been tried on high surface area carbon materials. Here we have made an extensive study of SMS on carbon structures obtained from different types of wood.     

水泥熟料与辅助性胶凝材料优化匹配的基础研究进展(Ⅱ)——化学效应

在分析水泥熟料与辅助性胶凝材料水化程度、填充能力和强度贡献率的基础上,提出了水泥熟料与辅助性胶凝材料优化匹配原则。利用该原则,可在降低水泥熟料用量、提高辅助性胶凝材料(特别是低活性辅助性胶凝材料)掺量的同时,显著改善复合水泥的强度、体积稳定性等性能,实现水泥熟料、矿渣等胶凝材料的高效利用。     

Elastin-Like Peptides (ELPs) – Building Blocks for Stimuli-Responsive Self-Assembled Materials

Elastin-like polypeptides (ELPs) are biopolymers composed of short repeating peptide motifs inspired by the native elastin hydrophobic domains, mostly the pentapeptide VPGXG, where X is a guest residue, which can be any amino acid except proline. The ability to control the hydrophobicity of ELPs, simply by changing the guest residue, and moreover, to transform an ELP from a soluble molecule to an insoluble one upon heating, makes them promising building blocks for novel stimuli-responsive self-assembled materials. Over the past decade, ELPs have been designed to self-assemble into spherical and cylindrical micelles, fibres, vesicles, and coacervates. In this short review, we summarize the recent literature, describing the molecules and conditions employed to attain these desired structures.     

Understanding electrocaloric cooling of ferroelectrics guided by phase-field modeling

With the urgent need to explore low-cost, high-efficiency solid-state refrigeration technology, the electrocaloric effects of ferroelectric materials have attracted much attention in the past decades. With the development of modern computing technology, the phase-field method is widely used to simulate the evolution of microstructure at mesoscale and predict the properties of different types of ferroelectric materials. In this article, we review the recent progress of electrocaloric effects from phenomenological Landau thermodynamics theory to phase-field simulation by discussing the microcosmic composition, mesoscopic domain structures, macroscopic size/shape, and external stimulus of strain/stress. More importantly, in searching for new ferroelectric electrocaloric cooling materials, it is possible to find materials whose free energy barrier height changes rapidly with temperature, such materials have a faster change rate with polarization temperature in terms of ferroelectric macroscopic properties, from them could get superior electrocaloric effects. We compile a relatively comprehensive computational design on the high performance of electrocaloric effects in different types of ferroelectrics and offer a perspective on the computational design of electrocaloric refrigeration materials at the mesoscale microstructure level.     

Stimuli-Responsive Polymeric Nanomaterials for the Delivery of Immunotherapy Moieties: Antigens,Adjuvants and Agonists

Immunotherapy has been investigated for decades, and it has provided promising results in preclinical studies. The most important issue that hinders researchers from advancing to clinical studies is the delivery system for immunotherapy agents, such as antigens, adjuvants and agonists, and the activation of these agents at the tumour site. Polymers are among the most versatile materials for a variety of treatments and diagnostics, and some polymers are reactive to either endogenous or exogenous stimuli. Utilizing this advantage, researchers have been developing novel and effective polymeric nanomaterials that can deliver immunotherapeutic moieties. In this review, we summarized recent works on stimuli-responsive polymeric nanomaterials that deliver antigens, adjuvants and agonists to tumours for immunotherapy purposes.     

Comparison of the Influence of Silica‐rich Supplementary Cementitious Materials on Cement Mortar Composites: Mechanical and Microstructural Assessment

Silicon - The silica-rich supplementary cementitious materials (SCMs) are the key components of mechanical and microstructural properties. The use of SCMs results in improving the mechanical and...     

Design and function of smart polymer gels based on ion recognition

Stimuli-responsive polymer gels can drastically change their volume in response to various external physical and chemical stimuli. The smart polymer gels for specific chemical substances have been extensively studied as applications for molecular recognition or supramolecular chemistry in the material sciences toward intelligent materials. This review article highlights recent advances in the molecular design of stimuli-responsive polymer gels triggered by molecular recognition, especially by the recognition of ionic species.