Current Smart Materials - Volume 4, Issue 1, 2019

Electronic skin (e-skin) is an artificial skin that mimics the sensing capabilities of human skin, which brings many potential applications in robotics, artificial intelligence, prosthetics, and health monitoring technologies. Many attempts associated with various mechanisms/approaches and materials/structures have been developed to match the e-skins to the particular functions of specific applications. Along the time, high sensitivity, mechanical flexibility/stretchability, multifunction, and large area are common driving forces in the research area. New materials, with a variety of structures and unique properties, offer a plenty of freedoms in designing and fabricating e-skins. Significant progress has been made in recently years. This paper firstly reviews the most recent progress on nanomaterial- based e-skins according to four major sensing mechanisms, with an emphasis on the effects of various materials on the sensitivity and stretchability of e-skins. Then the paper updates the progress and effort with respect to multifunctional e-skins and organic-thin-film-transistor based large-area e-skins. Further development possibilities are also briefly discussed.

It is generally known that MR fluid is a kind of designed materials whose rheological properties are controllable with the application of an external magnetic field. Based on these features, MR dampers have gained much attention of researchers owing to their salient properties such as controllable damping force and relatively fast response time. This article offers a recent review on the MR damper technology, particularly focusing on the application to various fields. Conceivable limitations, challenges, and comparative advantages of MR damper are critically analyzed. In order to promote the practical use of MR damper in application from the automobile to the military sector, this review summarizes different MR dampers and their significant contribution.

It is critically important to protect civil structures from unpredictable events, including earthquakes and strong winds, as well as maintaining their structural integrity and serviceability. To this end, considerable attention has been paid on the research and development of aseismic technology. This paper provides a literature review on the recent progress of Magnetorheological Elastomer (MRE) and the development and application of MRE devices on structure control technology. Firstly, this paper reviewed the investigations into the MR effect, mechanical property of MRE and its ingredients during the past decades. Then, research interests arising in the implementation and development of smart devices using MREs on structure control will be systematically reviewed. Basically, MRE base isolation and MRE based tuned mass damper are two major technologies to attenuate structural vibration, which will be the main focus of this paper.

Biochemical applications of polysaccharide are often demonstrated in various drug delivery systems and bone tissue engineering. Perhaps they are similar in biochemical properties with human components of the extracellular matrix, the body recognized them easily. In this manuscript, the polysaccharides, such as chitosan chitin, carrageenan, chondroitin sulfate,and cellulose used as scaffolds for bone regeneration, are discussed. Scaffolds have a porous structure which is extremely interconnected & permits cell penetration. They provide a 3-dimensional environment for bone regeneration. Polysaccharides such as chitosan have great mechanical characteristics and biocompatibility. Present manuscript deals with the polysaccharides based scaffolds that should possess osteoconductivity, biocompatibility,and mechanical strength like property during the tissue repairing process.They also show decreased degradation rate which means that they are present for tissue regeneration for an extended period of time. So it can be concluded that the polysaccharide-based scaffolds have good mechanical strength and stimulate the natural extracellular of bone for the regeneration process. In this manuscript, various patentsbased on applications of polysaccharide in bone marrow and tissue regeneration is also included.

Background: The superabsorbent polymers based conducting hydrogel such as polyaniline impregnated polyacrylate-starch hydrogel were synthesized via two -steps interpenetrating polymer network process. In the present work instead of using a synthetic polymer of acrylamide, a biodegradable polymer such as starch has been used with polyacrylate superabsorbent polymer. The main attempt of this work is to analyze the electrical conductivity of resulting hydrogel at varying concentrations of crosslinker, initiator, monomer, and a copolymer for improving the properties of synthesized hydrogel and elaborating the diversity of its utilization. Methods: The polymerization of aniline was performed through the absorption of aniline monomer into the polymer matrix followed by the addition of initiator/dopant solution. The morphological and structural analysis and thermal stability of the synthesized hydrogel were studied using Scanning Electron Microscopy (SEM), Fourier transform infrared spectroscopy and thermogravimetric analysis (TGA), respectively. The swelling behaviour of the synthesized hydrogel was performed in a different medium. Results: Electrical conductivity data of polyacrylate-starch/polyaniline (PAANa-starch/PANI) were compared from polyacrylate-co-polyacrylamide/polyaniline P(AANa-co-AM)/PANI hydrogel, which revealed that polyacrylate-starch/polyaniline shows higher conductivity than polyacrylate-co-polyacrylamide/ polyaniline conducting hydrogel. Maximum swelling of the synthesized hydrogel was reported in the basic medium. Conclusion: It is observed that the addition of starch into the matrix significantly improved the overall properties of hydrogel. The polymerization of aniline was done in-situ with the absorption of aniline monomer into the PAANa-starch polymer matrix followed by soaking in an initiator/dopant solution. The XRD pattern of PAANa-starch/PANI showed a broad peak at 22.8o while no peak was observed in the PAANa-starch gel, implying that PAANa-starch/PANI has a crystalline and more ordered structure. PAANa-starch/PANI has higher conductivity than the P(AANa-co-AM)/PANI hydrogel. This enhanced electrical conductivity in case of PAANa-starch/PANI hydrogel could be due to the more crosslink points of synthetic polymer polyacrylamide between PAANa-PANI hydrogel.

Background: Zinc oxide (ZnO) is one of the most attractive II-VI semiconductor oxide material, because of its direct wide band gap (3.37 eV) and large binding energy (60 meV). Zinc oxide (ZnO) is a promising semiconductor due to its optimised optical properties. Among semiconductor nanostructures, the vertically aligned one-dimensional ZnO nanorods are very important for nano device application. Methods: Vertically aligned ZnO nanorod arrays were grown on ZnO, aluminum doped ZnO (ZnO:Al), tantalum doped ZnO (ZnO:Ta) and aluminum and tantalum co-doped ZnO (ZnO:Al,Ta) seed layer by hydrothermal method. Results: The X-Ray Diffraction (XRD) investigation indicated the presence of hexagonal phase for the both seed layers and nanorods. The Scanning Electron Microscope (SEM) images of ZnO and doped ZnO seed layer thin-films show spherical shaped nanograins organized into wave like morphology. The optical absorption spectra revealed shift in absorption edge towards the shorter wavelength (blue shifted) for ZnO nanorods grown on ZnO:Al, ZnO:Ta and ZnO:Al,Ta seed layer compared to ZnO nanorods grown on ZnO seed layer. Conclusion: The increase in band gap value for the ZnO nanorods grown on doped ZnO seed layers due to the decrease in crystallite size and lattice constant as evidenced from XRD analysis. The unique property of Al, Ta doped ZnO can be used to fabricate nano-optoelectronic devices and photovoltaic devices, due to their improved optical properties.

Background: As an intelligent material, Magnetorheological Elastomer (MRE) has attracted extensive attention due to their excellent magnetic-induced properties. Aim: In addition to the matrix and interface, magnetic particle is the most critical factor in the magnetic properties of MRE. Particle size does not only affect on the magnetic properties of MRE, but also affects on interface and particle distribution. Therefore, studying the influence of particle size on viscoelastic properties is of great significance for the MRE. Methods: In this paper, several kinds of MREs containing Carbonyl Iron Particles (CIPs) with different sizes were prepared and characterized. The influences of frequency, strain and magnetic field on viscoelastic properties of these MRE samples have been discussed comprehensively. Result: The result shows that the particle size has a great impact on the performance of MRE, which indicates that the MRE performance can be improved by optimizing the particle size selection. In addition, possible physical mechanisms have been proposed to explain the effect of particles on MRE performance. Conclusion: This work can provide guidance for the performance improvement of MREs.

Background: Studies on the formation of colloidal crystals in concentrated suspensions have mainly been based on dispersed suspensions with a repulsive inter-particle potential of hard or nearly hard spheres. The self-assembly in weakly-flocculated suspensions has still been unrealized. Here, we report on the formation of ordered structures in concentrated suspensions of nearly-hard spherical particles with weakly-attractive inter-particle interactions that are an order of magnitude higher than the particles’ thermal energy. Methods: In our case, the self-assembly in such suspensions is not thermodynamically driven, but an external shear force must be applied. The driving force for the particles’ ordering is an increase in the inter-particle interactions. This manifests itself in a decrease in the average angle between the interparticle interaction direction and the applied shear stress direction. Results: For a successful ordering into a large-scale closed packed assembly, the external shear force must not exceed the inter-particle attractive interaction for the minimum possible average angle (as in the closed packed structures) but be high enough to enable the particles to move in the highly loaded suspension. Conclusion: The developed method for the self-assembly of the weakly flocculated systems can be applied very generally e.g. a control over a composition of heterogeneous colloidal crystals, manufacturing of the large-scale photonic crystals or preparation of very densely packed compacts of particles needed for the production of sintered ceramics.

Objective: This paper presents controllable force ranges of tactile devices made of smart Magnetorheological Fluids (MRF) and porous sponges (MR sponges in short). Methods: In order to identify the wide controllable range of the field-dependent repulsive force, three MR sponge samples with three different MR fluids are fabricated using polyurethane foam and cling film. Then, the repulsive forces of the samples are measured using the motor-driven experimental apparatus and the results are presented with minimum and maximum values of the repulsive forces. On the other hand, in order to investigate the feasibility of the proposed tactile device for application to Robot-assisted Minimally Invasive Surgery (RMIS), pig’s organs such as liver, lung and heart, whose viscoelastic properties are very similar to those of human tissues, are tested under same conditions. Results: It is shown that the range of the repulsive spectrum of the pig’s organs can be achieved using the proposed samples by controlling the magnetic field intensity to be applied to MRF domain.