Smart Materials

Research Progress on Preparation and Application of Conductive Fabrics Article

MA Feixiang,DING Chen,LING Zhongwen,YUAN Wei,Meng Xiuqing,SU Wenming,CUI Zheng

Materials Reports 2020,34(1 ):1114 -1125. DOI:10.11896/cldb.19110040

Abstract （1601）

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Recent Progress in Artificial Muscles Fibers Article

WANG Yulian, DI Jiangtao, LI Qingwen

Materials Reports 2021,35(1 ):1183 -1195. DOI:10.11896/cldb.20030153

Abstract （1723）

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Save Artificial muscle research is a highly interdisciplinary field that has been developing rapidly in the past three decades. Artificial muscle refers to a kind of material that will undergo structural change and will consequently be deformed when exposed to external stimuli such as voltage, current, temperature, pressure, light, and humidity. It plays an important role in various applications such as soft robots, artificial limbs, exoske-letons, and temperature-regulating clothing. According to their macroscopic appearance, artificial muscles can be classified into membranous muscles and fibrous muscles, in which the former, through their coiled structure, can convert the external-stimuli-induced volume expansion into radial rotation and axial contraction, and thus can achieve rotational actuation and contractile actuation, respectively, exhibiting obvious superiority to some existing membranous actuators in energy conversion efficiency, power density, and working performance. In addition, artificial muscles yarns can be knitted and woven into sophisticated structures which are capable of performing desired movements far more complicated than contraction and rotation, and which have excellent mechanical properties, good flexibility and similarity to natural biological muscles. Moreover, artificial muscles fibers can be actuated by various approaches such as thermal expansion, solvent/gas adsorption or infiltration, electrochemical double-layer charge injection, or even compressed air (pneumatic actuating).
In recent years, there has been tremendous success in the study of artificial muscles produced from flexible fibrous materials. Artificial polymer fibers, artificial inorganic fibers, and natural fibers, owing to their inherent flexibility, are the main raw materials.
In this review, we highlight the state-of-the-art researches on fibrous artificial muscles from the perspectives of constituent materials, working mechanisms, actuating modes, evaluative parameters, and relevant intelligent fabrics which can be obtained. We also discuss critically but briefly some key obstructive issues in this field.

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Recent Advances in Flexible Artificial Synapses Towards Intelligent Human-Machine Interface and Neuromorphic Computation Systems Article

LU Qifeng,SUN Fuqin,WANG Zihao,ZHANG Ting

Materials Reports 2020,34(1 ):1022 -1049. DOI:10.11896/cldb.19100063

Abstract （1856）

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Save Benefiting from the fast progress of artificial intelligence, a number of evolutions in the areas of human-machine interface, bio-inspired sensing systems, robots and prosthetics have been achieved. However,because of data explosion and the requirement for intelligent human-machine interaction, novel technology should be developed to overcome current bottlenecks. Different from existing extensive-energy-consumption neural networks implemented at the software level based on the conventional von Neumann architecture, the human brain only has a power consumption of about 20 W. Therefore, it is of a great importance to design a new neuromorphic computing system that is executed by parallel operation with high speed and low power consumption resemble to the human brain. Artificial synapses, either based on transistor or memristor structure, can be used as basic building blocks to achieve large-scale neural network parallelism. In addition, the spike based information processing in biological systems can also be mimicked with the employment of thue artificial synapses, which is beneficial to the construction of intelligent human-machine interface. Therefore, much efforts have been made to optimize the performance of the synaptic devices in terms of materials, fabrication process and structures. Consequently, a series of biorealistic synaptic behaviors, such as visual information reprocessing, movement control and learning-forgetting process, have been emulated using flexible artificial synapses.
Despite the great achievement in the study of artificial synapses, several underlying mechanisms have not been uncovered. First, the modulation of the post-synaptic signals varies from each individual, which requires specific analysis in order to make it to be compatible with the neural signal. In addition, dendrites in biological systems can collect, integrate, and modulate thousands of pre-synaptic input signals, and transmit these signals to post-synaptic neurons. That is to say, spatiotemporal information can be modulated. Therefore, exploration of the underlying mechanism and optimization of the device structure mimicking the biological dendrite can contribute to the simulation of dynamic logic induced by spatiotemporal synaptic stimulation. Besides, most of the reported researches were performed on the rigid substrates, which are not compatible with the biological systems. Therefore, fabrication of the devices on flexible substrates and investigation of the relationship between the electrical properties and interface quality are critical.
Herein, an overview of the recent progress of the artificial synapses is presented in terms of device structure, material selection, and working mechanism. Future challenges, research directions, and possible applications are also discussed. This review is hoped to provide a guidance for the design and fabrication of the flexible artificial synapses towards neuromorphic computing and intelligent human-machine interface.

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Novel Flexible Resistive Sensors in the Age of Intelligence Article

LUO Zewei,TIAN Xiyue,FAN Jichen,YANG Xin,FAN Tianyi,WANG Chaolun,WU Xing,CHU Junhao

Materials Reports 2020,34(1 ):1069 -1079. DOI:10.11896/cldb.19100149

Abstract （1019）

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Save Sensor is an important device to convert external physical excitation into electrical signals. With the development of Internet of Things, biomedical, artificial intelligence, the requirements of sensor properties are getting stringent. Researchers are constantly developing novel sensors to meet the growing demand. Recently, researchers have actively carried out relevant work on flexible sensors with new materials, new structures and high performance. The technologies such as material selection, structure control and preparation process are continuously deve-loped. The sensing principle of the flexible resistive sensor is to convert the applied pressure signals into electrical signals. The flexible resistive sensor with excellent performance has high sensitivity, high linearity, large working range, fast response and repeatability.
The microstructure of the sensor is the main regulator of the property. The traditional sensor characterization method can only measure the structure of the device statically, but it cannot dynamically monitor the change of material structure and chemical composition which influence the electronic property under the working condition in real time. The emergence of in situ characterization technology can solve the problems above and provide intuitive experimental support for improving sensor property. At the same time, a simple sensor cannot meet the technical needs in the age of information. It is no doubt that intelligent integrated and arrayed system is the trend of future sensor technology development. The intelligent sensing system possesses the function of collecting signals by the flexible resistive sensor and connecting the sensor with the designed integrated circuit. After transmitting and processing, the data is processed by artificial intelligence neural network algorithm. The results are transmitted to the intelligent display terminals where users can check the information and data analysis result.
In this review, we place particular emphasis on the progress of intelligent flexible resistive sensors. The microstructure and property research in sensors using the in situ characterization technique is clarified. Additionally, how to construct the intelligent sensing system based on flexible resistive sensor is also illustrated. Finally, we summarize recent development trends and application forecasts, especially the challenges in combination with intelligent system.

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Research Progress and Development Bottleneck of the Smart Imprinted Polymer Article

ZHANG Xiaoyan, SUN Yuan, LI Hui, CHEN Zhenbin

Materials Reports 2020,34(15 ):15163 -15173. DOI:10.11896/cldb.19070026

Abstract （923）

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Save Some intrinsic advantages, such as structural predetermination, long-term stability, wide applicability, specific recognition, added to the superiority of cost and preparation technology, make imprinted polymers (IPs) displaying potential application prospect in separation science, solid phase extraction, chromatographic separation, drug controlled release, chemical sensing, environmental detection, electrochemistry, membrane separation and many other fields, which, in fact, provide a foundation material basis and technical support for the accurate separation of templates. Nowadays, with the concept of sustainable development and circular economy accepted increasingly. IPs will be focused more as a research hotspot in the field of high performance functional materials inevitably.
However, IPs prepared by the traditional method is a highly cross-linked polymer, and the high cross-linking degree endowing IPs advantages of stable structure and strong recognition. However, owing to the simple and mechanical molecular recognition mechanism resulted from high cross-linking degree, IPs prepared by traditional method lacked the necessary "flexibility" and sufficient sensitivity to external stimulation conditions, which resulted in the difficulty to balance the desorption rate, selectivity and reusability during the separation and purification process, and further limited them application in practical industrial separation. In recent years, researchers' interest has gradually shifted to smart imprinted polymers that can improve the “flexibility” of traditional IPs.
A new type of functional material, namely smart imprinted polymers (S-IPs), was prepared by combining smart polymers (SPs) with imprinted polymers (IPs). It not only has the specific selectivity of common imprinted polymers, but also has the characteristics of responsiveness to external stimuli and reversibility of deformation, which makes them more excellent in adsorption and desorption. Research on S-IPs had achieved series of exciting results. Studies had successfully prepared temperature-sensitive IPs (T-IPs), magnetically responsive IPs (M-IPs), pH-sensitive IPs (pH-IPs), photoresponsive IPs (P-IPs) and dual-sensitive IPs (pH-M IPs, pH-T IPs, TM IPs, PM IPs, etc.) and multiple-sensitivity S-IPs, and all above had presented strong prospects in areas such as drug delivery, biotechnology, separation science and sensor etc.
This paper mainly reviews the research progress of S-IPs in intelligent mechanism and preparation method. Finally, key bottlenecks that hold back the development of S-IPs are summarizes, and the potential development prospect is concerned.

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Research Progress of Titanium-based High-temperature Shape Memory Alloy Article

LI Qiquan,LI Yan,MA Yuehui

Materials Reports 2020,34(3 ):3142 -3147. DOI:10.11896/cldb.19030262

Abstract （1612）

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Save Shape memory alloys have become important smart materials due to their unique shape memory effect and superelastic properties, showing great promising in aviation, aerospace, electronics, automotive and medical applications. The binary near-equiatomic nickel-titanium alloy is one of the most well-developed shape memory materials, but it is very difficult to be used at very high temperature (>100 ℃, 373 K). The high-temperature service environment represented by aviation, aerospace, nuclear reactors, etc. urgently requires shape memory alloy materials with high phase transformation temperature and good combined properties. Therefore, the development of high-temperature shape memory alloy has become a research focus and difficulty in this field. In recent years, researchers have used the new titanium-based alloys as research objects to obtain shape memory materials with high martensitic transformation temperature through the design of alloying elements, and developed new high-temperature shape memory alloy systems such as Ti-Ta based, Ti-Zr based, Ti-Nb based and Ti-Mo based alloys. On the basis of satisfying the high temperature phase transformation characteristics, these alloy systems exhibit different performance characteristics. For example, Ti-Ta based alloys can effectively inhibit the precipitation of ω phase by Ta element and improve the plasticity. Ti-Nb based alloys have good processing ability. In addition, the alloying elements such as Pd, Pt and Au can be used in alloys to further increase the phase transition temperature. The addition of elements such as Sn, Al, and Ga can appropriately lower the alloy transformation temperature and improve its mechanical properties and functional properties.
In this paper, the research progresses of several high-temperature shape memory alloy systems such as Ti-Ta based, Ti-Zr based, Ti-Nb based and Ti-Mo basedalloys are reviewed. The effects of alloying elements on phase transformation temperature, shape memory effect and mechanical properties of alloys are analyzed. This paper gives comprehensive summary of the performance advantages and defects of various alloys, and proposes the development direction of new high temperature shape memory alloy materials in the future.

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Effect of Annealing Temperature on Memory Behaviors and Mechanical Properties of Ti-50.8Ni-0.1Zr Shape Memory Alloy Wire Article

YE Junjie, HE Zhirong, ZHANG Kungang, FENG Hui

Materials Reports 2021,35(4 ):4118 -4123. DOI:10.11896/cldb.19100010

Abstract （771）

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A Survey on the Study of Biomass-based Thermosensitive Smart Materials Article

LIU Dexiang, LIU Wu, YE Zhihui, WU Zhiping

Materials Reports 2019,33(19 ):3336 -3346. DOI:10.11896/cldb.18070135

Abstract （1175）

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Save Thermosensitive materials are recognized as one of the most significant smart materials at present. Thermosensitive homopolymers show superior environmental sensitivity, nevertheless they suffer from poor mechanical properties, which cannot meet the applied requirements. Furthermore, it is difficult to alter the lower critical solution temperature (LCST) of some thermosensitive polymers, which blocks their widespread application. The combination or graft copolymerization of the thermosensitive materials with other substrates will greatly contribute to the properties of thermosensitive polymer. Meanwhile, the critical temperature of some thermosensitive materials can be adjusted by changing the material composition or ratio, thus their application field can be expanded.
The majority of the raw materials for preparing the thermosensitive materials are derived from non-renewable petroleum resources. The growing deficits of petroleum resources has given impetus to seek other alternative resources. Biomass, as a renewable resource, is widely distributed in nature, showing the advantages of abundant reserves and sustainable utilization. Especially, their active functional groups, including hydroxyl, amine, ether and carboxyl groups, can provide a variety of active sites, which is an ideal substrate for preparing thermosensitive materials by graft copolymerization with thermosensitive monomers. Biomass materials that have been successfully applied in biomass thermo-sensitive smart materials include cellulose, cellulose ether, hemicellulose, lignin, chitosan, etc. However, the graft copolymerization method for preparing biomass-based temperature-sensitive smart materials is short of diversity. The temperature-sensitive materials prepared by conventional free radical copolymerization bear the narrow temperature response range, large generation of homopolymers difficult to separate, and single morphology of mate-rial. The approach of graft copolymerization of biomass thermosensitive materials has developed from common free radical polymerization by initiators to highly controllable free radical polymerization for photoinitiated free radical polymerization, atom transfer radical polymerization(ATRP), single electron transfer mediated living radical polymerization (SET-LRP), reversible addition-fragmentation chain transfer (RAFT). A variety of thermosensitive monomers can be selected, among them, N-isopropylacrylamide (NIPAM) received most research attentions. It possesses a clear critical solution temperature, a close LCST with human body temperature. The thermosensitive membranes, thermo-sensitive hydrogels and thermo-sensitive microspheres prepared by NIPAM together with biomaterials exhibit extensive application in drug release, tissue engineering, industrial and agricultural, etc.
In this article, we present a detailed overview of the approaches for preparing temperature sensitive materials by biomass macromolecules, summarize the character of the grafting copolymerization, and introduce the temperature-sensitive substances involved in the preparation of thermo-sensitive materials, mechanism of temperature response and the application of biomass thermosensitive materials. Finally, we point out the difficulties existing in the preparation and application of biomass thermosensitive smart materials, and the future development of technology.

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Progress on Stimulus Responsive Smart Hydrogels Based on Natural Polymers Article

FAN Zhiping, CHENG Ping, ZHANG Demeng, WANG Wenli, HAN Jun1,

Materials Reports 2020,34(21 ):21012 -21025. DOI:10.11896/cldb.19080216

Abstract （1966）

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Save atural polymer based hydrogels have been extensively studied in the field of biomedicine due to their excellent biocompatibility, biodegra-dability and biological characteristics. The rapid development of advanced industries, such as flexible devices and biomimetic materials, has further expanded their application fields. Stimulus responsive hydrogel is a kind of intelligent materials, whose network structure can undergo deformation and phase transformation in response to external environmental triggers, resulting in a swelling-shrinking or gel-sol transition behavior. The combination of specific responsive functional groups and materials with natural polymers is usually the main method to give hydrogel stimuli responsiveness.
Although traditional hydrogel materials are available, some products still have the following problems: ⅰ. It contains a large number of synthetic polymers, and the synthesis process is complex, high energy consumption and cost; ⅱ.The biocompatibility and degradability of hydrogels are not good, which are not suitable for a series of high-end medical fields, such as implants. ⅲ. After hydrogel forming, the performance is single and immutable, unable to achieve “intelligent” response to external stimuli, and the field of application is severely limited.
Compared with traditional hydrogels, stimulus responsive hydrogels have attracted much attention due to their spatial, temporal sensitivity. Re-levant products with multiple, variable and controllable performances have greatly broadened their application fields. In recent years, the vigorous development of natural polymers has provided new opportunities for stimulus responsive hydrogels. At present, the research on natural polymer based stimulus responsive hydrogels mainly focuses on the following aspects: ⅰ. Development of high-end biomedical hydrogels with excellent basic properties and good biocompatibility, biodegradability. ⅱ. Focusing on natural polymer structural modification, giving multiple stimuli responsive properties of materials and preparing multifunctional, multifunctional hydrogels. ⅲ. Development and application of novel non-contact stimulator. ⅳ.Clinical transformation of products with definite efficacy.
This review mainly focuses on the design methods, behavior mechanisms and recent application progress of natural polymer based hydrogels with temperature, light, pressure, electrical, magnetic, pH, redox, ionic, sugar and enzymatic responses. Finally, a perspective on the future research directions of natural polymer based hydrogels is briefly discussed.

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The Systematic Project Involving Brazes Development and Intelligent Brazing Technology Innovation: a Materials Genome Perspective Article

HE Peng, LIN Panpan

Materials Reports 2019,33(1 ):156 -161. DOI:10.11896/cldb.201901018

Abstract （1087）

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Save In recent years, the conventional material research methodologies depending on scientific intuition and trial and error have been increasingly regarded as the bottleneck for development and technological advance of manufacturing industry. Then, the innovation on material research methodology has become the international new trend of materials research and development. Materials genome technology is considered as a giant leap of materials S&T and the accelerator of new material development. The complexity and randomicity of brazing process make the design and development of brazing materials more complicated and time-consuming than ordinary materials. Materials genome initiative, as a brand new concept for advanced materials development, should also be adopted to the performance optimization and development of new brazing materials. This is of great significance to promote the rapid development of welding technology, especially intelligent welding.
The three main facets of materials genome technology are high-throughput material computation, high-throughput material experimentation and material basic data. Large-scale high-throughput computation can provide abundant and systematic data. High-throughput material experimentation can quickly verify these data. Moreover, the establishment of the material database can realize (i) the effective integration of calculated data with experimental data, and (ii) their mutual complementation and mutual verification. These three elements work together and then contribute to a more close relationship between theoretical and experimental research in the process of material development. This can shorten the period of research, manufacturing and application, and reduces the development cost of new materials.
In addition to the performance of material itself, developing new brazing materials also need to consider (i) physical and chemical compatibility of brazing materials and base materials, (ii) interaction (diffusion and formation of new phase) between brazing materials and base materials during brazing process. The interaction between brazing materials and base materials is very complex, as it not only depends on the brazing process (temperature, holding time, pressure, atmosphere, etc.), but is directly related to the composition of brazes and base materials. Therefore, compared with ordinary materials, the design and development of brazing materials require a more complicated methodology and a more time-consuming course. And the initiation of brazing materials genome project is of great urgency. This relies to a considerable degree on the satisfactory achievement towards three essential engineering issues, i.e. development of high-throughput computing software, high-throughput experimental methodologies and data integration system.
The development of intelligent welding at present has focused mostly on fusion welding, e.g. arc welding, laser welding, etc., and has also acquired notable achievements. However, the full-intelligent control technology for brazing still lies at a fairly primitive level, and the current researches concentrate mainly on brazing equipment and brazing process control. The brazing materials play an important role in intelligent brazing. So the brazing materials genome project can facilitate the intelligentization of brazing technology. In return, the advancement of intelligent brazing will also advance the course of brazing materials genome project, as it will greatly simplify and accelerate the performance examination upon new designed brazes, and in addition, it will help to collect more real-time data for the numerous artificially created brazes.
This paper discusses the three basic elements of materials genome technology and the corresponding global research status. It also analyzes the influence factors and key common problems for the adoption of materials genome technology to brazing materials development, and states dialectically the mutually reinforcing relationship between brazes genome project and intelligent brazing technology.

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4D Printing: Technologies, Materials and Applications Article

ZHANG Yumeng, LI Jie, XIA Jinjun, ZHANG Yuxin

Materials Reports 2021,35(1 ):1212 -1223. DOI:10.11896/cldb.20030128

Abstract （1893）

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Save Since the 1980s, the idea of 3D printing has set off a research upsurge. Due to its advantages of material efficiency, excellent surface resolution and high efficiency in one-step production, 3D printing has been widely used in biomedical, electronics, self-healing technology, engineering applications and bionics fields. However, 3D printing technology also has some shortages, it cannot control the addition technology to produce complex structure or suppress the size change and anisotropy behavior of strain control. In order to overcome the complexity and inflexibility of printing size, people introduced the concept of 4D printing. 4D printing is an interdisciplinary research based on intelligent materials, 3D printers and design. Compared with the static structure produced by 3D printing, 4D printing contains a dynamic structure which means 4D allows 3D printed structures to respond to external stimuli (such as temperature, light, water, etc.) and change their shape or function over time, so that the printed product is no longer limited to a fixed shape, but presents a variety of changes.
4D printing attracts a lot of interest since it was first conceptualized in 2013. The fourth dimension gives vitality to design, which uses stimuli to drive the transformation of smart materials by shape memory effects. Intelligent materials are sensitive to the environment which including polymers, alloys, hydrogel, ceramics, composite materials and so on. Through the environment stimuli like thermal pre-strain, water absorption, electromagnetic radiation, activation, magnetic field, current, voltage, the solvent and pH, smart materials will self-assembly produce a deformation, decomposition, repair even change the properties or functions, showing a variety of morphological characteristics. 4D printing has been widely tried in drug delivery, wearable electronics, fashion, automatic origami structures, sensors and other engineering applications by mimicking natural processes (flowers bloom, plant changes and sunflower movements) and exploring similar characteristics of materials.
This review focuses on the system and specific application of 4D printing materials and list a brief overview of the 4D printing about its history, definition, principle and basic composition. We look back the latest development of 4D printing materials and state both the development and challenges of related application fields like the biological bionic, biological, medical, the progress of the application of paper folding structure, etc. Finally, we introduce the trend of 4D printing and the development prospect of the new field to provide reference for further research.

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