Multifunctional Smart Materials Research Articles

Engineering Dental Tissues Using Biomaterials with Piezoelectric Effect: Current Progress and Future Perspectives

Dental caries and traumatic injuries to teeth may cause irreversible inflammation and eventual death of the dental pulp. Nevertheless, predictably, repair and regeneration of the dentin-pulp complex remain a formidable challenge. In recent years, smart multifunctional materials with antimicrobial, anti-inflammatory, and pro-regenerative properties have emerged as promising approaches to meet this critical clinical need. As a unique class of smart materials, piezoelectric materials have an unprecedented advantage over other stimuli-responsive materials due to their inherent capability to generate electric charges, which have been shown to facilitate both antimicrobial action and tissue regeneration. Nonetheless, studies on piezoelectric biomaterials in the repair and regeneration of the dentin-pulp complex remain limited. In this review, we summarize the biomedical applications of piezoelectric biomaterials in dental applications and elucidate the underlying molecular mechanisms contributing to the biological effect of piezoelectricity. Moreover, we highlight how this state-of-the-art can be further exploited in the future for dental tissue engineering.

In Situ Activation of Superhydrophobic Surfaces with Triple Icephobicity at Low Temperatures.

Superhydrophobic surfaces have been widely studied due to their potential applications in aerospace fields. However, superhydrophobic surfaces with excellent water-repellent, anti-icing, and icephobic performances at low temperatures have rarely been reported. Herein, superhydrophobic surfaces with heating capability were prepared by etching square micropillar arrays on the surface of multiwalled carbon nanotube (MWCNT)/poly(dimethylsiloxane) (PDMS) films. The fabricated superhydrophobic surface has triple icephobicity, which can be activated even at low temperatures. The triple icephobicity is triggered by an applied voltage to achieve excellent water-repellent and icephobic capabilities, even at -40 °C. Additionally, theoretical calculations reveal that a droplet on a superhydrophobic surface loses heat at a rate of 8.91 × 10-5 J/s, which is 2 orders of magnitude slower than a flat surface (2.15 × 10-3 J/s). Also, at -40 °C, the mechanical interlocking force formed between the superhydrophobic surface and ice can be released by the heating property of the superhydrophobic surface. This low-energy, multifunctional superhydrophobic surface opens up new possibilities for bionic smart multifunctional materials in icephobic applications.

Performance tests and design of a series of magnetic fluid shock absorbers with varying stiffness based on optimal stiffness formula

With the rapid development of aerospace technology, the vibration problem of the spacecraft flexible structure urgently needs to be solved. Magnetic fluids are a type of multi-functional smart materials, which can be employed in shock absorbers to eliminate these vibrations. Referring to the calculation methods of stiffness coefficients of other passive dampers, the stiffness coefficient formula of magnetic fluid shock absorbers (MFSAs) was derived and refined. Meanwhile, a series of varying stiffness magnetic fluid shock absorbers (VS-MFSAs) were proposed and fabricated based on the second-order buoyancy principle. The range of stiffness coefficients covered by these VS-MFSAs contains the optimal stiffness coefficient estimated by formulas. The repulsive force measurement and vibration attenuation experiments were conducted on these VS-MFSAs. In the case of small amplitude, the relationship between the repulsive force and the offset distance was linear, which means the stiffness was linear. The simulation and experiment curves of the stiffness were in good agreement. The results of vibration attenuation experiments demonstrated that the rod length and the magnetic fluid mass influence the damping efficiency of VS-MFSAs. In addition, these results verified that the VS-MFSA with the optimal stiffness coefficient performed best. Therefore, the stiffness coefficient formula can guide the design of MFSAs.

Rhodamine-containing double-network hydrogels for smart window materials with tunable light transmittance, low-temperature warning, and deformation sensing

Smart window materials have attracted much attention because of their energy savings ability, light passage control in response to external stimuli, but most studies focus on the tunability of a single property, specifically, optical transmittance. Here, we report a rhodamine (Rh) mechanophore-functionalized PNIPAAm-based double-network (DN) hydrogel with the potential to act as multifunctional smart window materials that have the combination of a transmittance regulation ability, freezing−/compression-induced mechanochromic and mechanofluorescent properties. Benefiting from naturally reversible hydrophilic/hydrophobic phase transitions of PNIPAAm chains, DN hydrogels exhibit an excellent temperature-induced optical transmittance change between transparency and opaqueness. Because of the covalent incorporation of Rh mechanophores into the first network within DN hydrogels, the gels can display visualizable mechanochromism or mechanofluorescence upon freezing or compression. This is attributed to the generation of the colored and fluorescent ring-opened Rh spirolactams via mechanoactivation. This work is the first example of thermochromic smart window materials with a visualized low-temperature warning and damage sensing abilities and provides a new strategy to fabricate multifunctional smart window materials.

Printed 3D Gesture Recognition Thermoformed Half Sphere Compatible with In‐Mold Electronic Applications

The development of conformable electronic systems’ focuses on the multifunctional smart materials transform areas from the automotive industry to biomedicine, based on improved integration and advanced functionalities. In‐mold electronics (IME) combines thermoforming, injection molding, and printed electronics, resulting in sensing structural parts integrated into smart surfaces, communicating with computer systems, and enabling advanced experiences in terms of human‐machine interaction. Contrary to flexible electronics, designed as bend conductors around a single axis, thermoformed electronics allow deformations in the three‐axial directions for different geometries. Herein, a 2D screen‐printed pattern using conductive silver ink thermoformed into a spherical surface suitable for 3D gesture recognition is reported. The mechanical deformation of the high‐impact polystyrene sheet (HIPS) and polyethylene terephthalate‐glycol (PETG) substrates during the thermoforming process of the electrical circuit is characterized experimentally. The electrical resistance changes through the circuit in the stages of the fabrication process due the thickness decrease and the propagation of the small cracks. Both evaluations contribute to a better understanding of the performance of the materials when subject to the IME process. Validation of the 3D gesture recognition operation is carried out, demonstrating their full operability, as well as the possibilities that the combination of technologies allows.

Dynamic scaling properties of multistep polarization response in ferroelectrics

Ferroelectrics are multifunctional smart materials finding applications in sensor technology, micromechanical actuation, digital information storage, etc. Their most fundamental property is the ability of polarization switching under an applied electric field. In particular, understanding of switching kinetics is essential for digital information storage. In this regard, scaling properties of the temporal polarization response are well-known for 180°-switching processes in ferroelectrics characterized by a unique field-dependent local switching time. Unexpectedly, these properties are now observed in multiaxial polycrystalline ferroelectrics, exhibiting a number of parallel and sequential non-180°-switching processes with distinct switching times. This behavior can be explained by a combination of the multistep stochastic mechanism and the inhomogeneous field mechanism models of polarization reversal. Scaling properties are predicted for polycrystalline ferroelectrics of tetragonal, rhombohedral, and orthorhombic symmetries and are exemplarily demonstrated by the measurements of polarization kinetics in (K,Na)NbO3-based ferroelectric ceramic over a timescale of 7 orders of magnitude. Dynamic scaling properties allow insight into the microscopic switching mechanisms, on the one hand, and into statistical material characteristics, on the other hand, thereby providing the description of temporal polarization with high accuracy. The gained deeper insight into the mechanisms of multistep polarization switching is crucial for future ultrafast and multilevel digital information storage.

A Smart Molecule Showing Spin Crossover Responsive Aggregation-Induced Emission

A Smart Molecule Showing Spin Crossover Responsive Aggregation-Induced Emission

Eco-friendly synthesis of self-reporting robust superhydrophobic coatings with damage sensitive photoluminescence

Polymer-based superhydrophobic coatings have attracted tremendous attention as promising multi-functional materials. Nevertheless, the practical applications of superhydrophobic coatings are seriously restricted by the well-known drawbacks of the pollution-carrying fabrication methods (e.g., harmful fluorinated compounds and organic solvents employed) and the fragile mechanical durability. Meanwhile, the absence of the smart response to external stimulus is another restricted factor for application as a promising smart multifunctional material. It is highly challenging to synthesize desirable self-reporting robust superhydrophobic coatings for autonomously indicating internal damages or failure development in early stages with the eco-friendly method. In this paper, the self-reporting robust superhydrophobic coatings with damage-sensitive photoluminescence (PL) were prepared by the facile, non-fluorinated, and eco-friendly method. Both the surface superhydrophobic modification of tetrapod-shaped ZnO (T-ZnO) and preparation of superhydrophobic coating were implemented with the waterborne formula. Benefited from the isotropic co-crosslinked interlocking networks constructed by covalent bonding the methacrylate copolymers onto the surface of T-ZnO and crosslinked with the methacrylate copolymers matrix, the as-prepared superhydrophobic coating showed excellent mechanical durability. The coating can still maintain high water-repellent (Contact angle (CA) = 150°) after 1000 cycles of severe mechanical abrasion. More importantly, the as-prepared superhydrophobic coating exhibited a significant PL response to the damage-related structural changes under mechanical abrasion. Furthermore, the anti-corrosion and self-cleaning properties of the as-prepared superhydrophobic coating were also evaluated. Under the merits in the synthesis method and the damage-related PL characteristics, the as-prepared superhydrophobic coating has a promising application in non-destructive detection and opens up the new possible application in engineering scopes.

Photo/Electrochromic Dual Responsive Behavior of a Cage-like Zr(IV)-Viologen Metal-Organic Polyhedron (MOP).

Stable stimulus-responsive materials are highly desirable due to their widespread potential applications and growing demand in recent decades. Despite the fact that viologen derivatives have long been known as excellent photochromic and electrochromic materials, the development of stable viologen-based multifunctional smart materials with short coloration times remains an exciting topic. To obtain photochromic and electrochromic dual responsive materials, embedding the viologen ligand into a robust metal oxide cluster to increase its stability and sensitivity is an effective strategy. Herein, a viologen-based metal-organic polyhedron (MOP) {[Zr6L3(μ3-O)2(μ2-OH)6Cp6]·8Cl·CH3OH·DMF} [Zr-MOP-1; H2L·2Cl = 1,1'-bis(4-carboxyphenyl)-4,4'-bipyridinium dichloride, and Cp = η5-C5H5] was successfully prepared and characterized. It consists of trinuclear Zr-oxygen secondary building units and exhibits reversible photochromic and electrochromic dual responsive behaviors. As expected, the designed robust viologen-based nanocage with a V2E3 (V = vertex, and E = edge) topology can maintain its stability and rapid photo/electrochromic behaviors with an obvious reversible change in color from purple (brown) to green, mainly due to the enclosed cluster structure and the abundant free viologen radicals that originate from the effective Cl → N and O → N electron transfers. Spectroelectrochemistry and theoretical calculations of this Zr-MOP were also performed to verify the chromic mechanism.

Dual Photo‐ and Mechanochromisms of Graphitic Carbon Nitride/Polyvinyl Alcohol Film

AbstractAn adaptable stimuli responsive system is proposed based on defective graphitic carbon nitride (d‐GCN)/polyvinyl alcohol (PVA) composite attached to different substrates. Nitrogen vacancies, introduced during synthesis via potassium doping, act as internal electron donors to enhance the photoreduction of redox dyes for quick reversible photochromism. This system can be applied as visible light responsive rewritable paper that offers high resolution for printed text, rapid activation/recoloration, multicolor functionality, and high cyclability. The defects also inhibit the d‐GCN particle growth resulting in smaller particle sizes over bulk samples, which enable the formation of transparent mechanochromic films. By altering the PVA/d‐GCN ratio in the composites, two mechanical stimuli responses are introduced by taking advantage of wrinkle and crack formation on the film surface. With a low d‐GCN concentration, mechanical scratching of the film causes the formation of surface wrinkles that alter the film transparency without damaging the film, allowing for text to be written on the surface that can be erased by moisture. With a high d‐GCN concentration, cracks developed on the surface scatter light when stretched, enabling the development of a strain dependent smart window. Both these mechanochromisms can be combined with the photochromism to develop multifunctional smart materials with widespread application.

Selective adsorption and detection of p-arsanilic acid on MOF-on-MOF heterostructure induced by nitrogen-rich self-assembly template

P-arsanilic acid (p-ASA), as a widely used feed additive, is potentially toxic to aquatic organisms and seriously affects the water environment. Therefore, the development of an intelligent multi-functional material for selective simultaneous detection and removal of p-ASA in water has become a top priority. Here, we report one case of novel nitrogen-rich two-dimensional metal–organic framework, Cu(I)-tpp (Htpp = 1-(4-(tetrazol-5-yl))3-(pyrzin-2-yl) pyrazol), which has outstanding fluorescence emission at 655 nm; and nitrogen-rich sites exposed on the surface make it an excellent self-assembly template to induce the formation of heterostructures. According to the target requirements, ZIF-8 is selected to construct the Cu(I)-tpp@ZIF-8 heterostructure by liquid-phase epitaxy ignoring the lattice mismatch problem. And the electronic structure of the Cu(I)-tpp framework is analyzed by electrostatic potential (ESP) to determine the nucleation site of ZIF-8. The prepared Cu(I)-tpp@ZIF-8 heterostructure assembles adsorption and fluorescence sensing properties, exhibiting significant adsorption (qmax = 303.0 mg g−1) and fluorescence quenching response (LOD = 0.4 µg·L−1) for p-ASA. Notably, Cu(I)-tpp@ZIF-8 achieves a special response to p-ASA that is different from other organic arsenic acids, especially compared with its isomer (o-ASA) and roxarsone (ROX). As a smart multifunctional material, Cu(I)-tpp@ZIF-8 realizes the specificity in the simultaneous detection and removal of p-ASA, presenting excellent application prospects in water quality monitoring.

A novel SMA-magnetorheological hybrid bracing system for seismic control

Maintaining the stability of civil structures under excessive dynamic loads, including earthquakes and windstorms, has always been a big challenge for researchers and designers in structural engineering communities. The recent integration of multi-functional smart materials into structural bracing systems has opened a new horizon in civil engineering to control and maintain the structural stability of civil infrastructures. A hybrid smart bracing system based on Magnetorheological Fluid (MRF) and Shape Memory Alloy (SMA) has been developed in the present study. To examine the performance and functionality of the developed model, numerical simulations are conducted under quasi-static load conditions. Compared to the individual SMA-based bracing and MRF-based bracing systems, the proposed hybrid system considers both active and inactive modes of the MRF-based system to illustrate its superiority and highlight its advantages. Additionally, the effect of the two most common SMA materials on the dynamic behavior of the bracing has been studied. The results show significant improvements in the energy dissipation capacity and the re-centering ability of the hybrid bracing system.

Electrical transport modulation of VO2/Si(111) heterojunction by engineering interfacial barrier height

Smart multifunctional materials such as vanadium dioxide (VO2), which exhibit a reversible semiconductor-to-metal transition (SMT), provide a new route toward engineering high speed switchable devices. Here, we present a detailed report on the modulation in the electrical properties of VO2/Si heterostructures by application of an external electrical field across VO2 thin films. Single-phase VO2 thin films have been deposited on an Si(111) substrate using the pulsed laser deposition technique. The electrical transport behavior across the VO2/Si heterostructure has been studied in the temperature range of 35–105 °C, and a reversible SMT can be seen at 68 and 63 °C for heating and cooling cycles, respectively. The temperature-dependent resistance of the device shows a hysteresis loop around the transition temperature of the VO2 thin film. In addition, the device shows a significant change in junction current when an external bias is applied on the VO2 thin film, and this phenomenon has been utilized to study the switching behavior of the device. Such behavior is due to the change in interfacial barrier height because of the bias dependent tilting of electronic energy bands of the VO2 thin film. Our results offer novel opportunities to externally control the electrical transport of vertical heterostructures and can be beneficial for extending the notion of electrical field modulation in electrical switches and sensors.

A dual perspective on the microwave-assisted synthesis of HCN polymers towards the chemical evolution and design of functional materials

In this paper, the first study on NH4CN polymerization induced by microwave radiation is described, where a singular kinetic behaviour, especially when this reaction is conducted in the absence of air, is found. As a result, a complex conjugated N-heterocyclic polymer system is obtained, whose properties are very different, and even improved according to morphological features, characterized by their X-ray diffraction patterns and scanning electron microscopy analysis, with respect to those produced under conventional thermal treatment. In addition, a wide variety of relevant bioorganics have been identified, such as amino acids, nucleobases, co-factors, etc., from the synthetized NH4CN polymers. These particular families of polymers are of high interest in the fields of astrobiology and prebiotic chemistry and, more recently, in the development of smart multifunctional materials. From an astrobiological perspective, microwave-driven syntheses may simulate hydrothermal environments, which are considered ideal niches for increasing organic molecular complexity, and eventually as scenarios for an origin of life. From an industrial point of view and for potential applications, a microwave irradiation process leads to a notable decrease in the reaction times, and tune the properties of these new series macromolecular systems. The characteristics found for these materials encourage the development of further systematic research on this alternative HCN polymerization.

High refractive index and third-order nonlinear optical susceptibility of nanostructured ZnSe/FTO thin films: Towards smart multifunctional optoelectronic materials

The present work aims to prepare the nanostructured ZnSe films with high quality onto a fluorine-doped tin oxide glass substrate (FTO/glass) by using the thermal evaporation technique. The X-rays diffraction was used to investigate the structural properties of ZnSe thin films onto FTO glass. The XRD main peaks are corresponding to FTO glass expect the [111], and [311] peaks are related to the ZnSe film. The atomic force microscope supports the nanostructured of the studied films. The linear and nonlinear optical parameters were evaluated and analyzed based on spectroscopic measurements. The dielectric constant and dielectric loss were calculated for ZnSe/FTO thin film. It is clear from the optical analysis and their related refractive index that the nanostructured ZnSe/FTO film has a high refractive index and high third-order nonlinear optical susceptibility. ZnSe/FTO optical system is recommended for the new generation of electronic and optoelectronic devices, especially for telecommunications and nonlinear media.

Hydration-induced reversible deformation of biological materials

The influx and efflux of water in biological structures actuates reversible deformation and recovery processes that are crucial for mechanical functions in plants and animals. These processes utilize various mechanochemical mechanisms: swelling directed by the arrangement of cellulosic microfibrils in a bilayer construct, which generates different deformation patterns; lignification gradients; hierarchical foam-like inner structures, some of which also include swelling by hygroscopic cellulose inner cell layer; turgor pressure, which is activated by osmosis and acts at the cellular level, generating reversible motions. In this Review, we present representatives of each of these four mechanisms: pine cones, wheat awns, the twisted opening of Bauhinia pods and the seed of the stork’s bill; the resurrection plant; ice plant seed capsules and carrotwood seed pod; the wilting and redressing of plant stems. Natural polymeric materials produced by animals can also exhibit hydration-driven shape and strength recovery: bird feathers and hair are prime examples. Spider silk — a non-keratinous biopolymer — also exhibits humidity-driven reversible deformation. After describing these animal-based mechanisms, we outline bioinspired applications to actuate multifunctional and biocompatible smart materials, and indicate future directions of research with potential for new bioinspired designs. The influx and efflux of water in biological structures leads to reversible deformation, which has important functions in plants (for example, in seed protection and dispersal) and animals (for example, in the recovery of the strength and shape of feathers, and for reversible changes in silk and hair). Here the authors review the main hydration-induced deformation mechanisms and highlight applications inspired by these processes.

Recent Advances in Antiinflammatory Material Design.

Implants and prostheses are widely used to replace damaged tissues or to treat various diseases. However, besides the risk of bacterial or fungal infection, an inflammatory response usually occurs. Here, recent progress in the field of anti-inflammatory biomaterials is described. Different materials and approaches are used to decrease the inflammatory response, including hydrogels, nanoparticles, implant surface coating by polymers, and a variety of systems for anti-inflammatory drug delivery. Complex multifunctional systems dealing with inflammation, microbial infection, bone regeneration, or angiogenesis are also described. New promising stimuli-responsive systems, such as pH- and temperature-responsive materials, are also being developed that would enable an "intelligent" antiinflammatory response when the inflammation occurs. Together, different approaches hold promise for creation of novel multifunctional smart materials allowing better implant integration and tissue regeneration.

Fabricated smart sponge with switchable wettability and photocatalytic response for controllable oil-water separation and pollutants removal

Stimuli-responsive materials with the controllable oil-water separation and water further purification abilities show great potential in practical applications. In this paper, a highly effective and eco-friendly smart pH-responsive melamine sponge with switchable wettability and photocatalytic activity was prepared via anchoring three-dimensional cell-like BiOCl microspheres into sponge skeletons and being modified by dodecanedioic acid and lauric acid. The obtained sponge shows rapidly switchable wettability and can separate various oil/water mixtures with high efficiency up to 99%. Moreover, the as-prepared smart sponge also demonstrates reliable photocatalytic ability and could remove the soluble pollutants (such as methylene blue and Sudan III) under visible light as well as UV light (degradation efficiency around 100%). Besides, the smart pH-responsive material showed satisfactory reusability and stability. This smart multifunctional material has outstanding potential in water resource purification.

Optimization of multifunctional nano cement composite for self – sensing

Abstract The invent of new construction materials and extensive research in concrete technology and cement chemistry has proved that apart from proportioning concrete for high strength it is very important to design a concrete mix for high performance in terms of diagnosing damage like smart materials. The use of mineral and chemical admixtures in concrete has facilitated the material scientists to invent special types of concrete to suit the current application. Materials that are used in concrete like steel fibres, carbon nano fires (CNF) and carbon nano tubes (CNT) with appropriate dosage, can impart this self-sensing property in concrete. These multifunctional smart materials have resulted in assessing the damage to structures without the need for any external sources like sensors or any structural health monitoring device like optical fibres. The inclusions of nano materials in cementitious matrix that are conductive in nature provide a new type of self-sensing composite. Self-sensing material have the ability to sense their own conditions like stress, strain, temperature and damage. This property of the material which enables itself to assess its own damage and deformation has made it a smart material for health monitoring. Appropriate use of this smart material with a well-defined sensing scheme can enhance the sensitivity of damage detection in micro level which can prevent the collapse of the structure. CNT and CNF were used in 0.1 to 0.3% by weight of cement and their electrical conductivity was measured which gives a good relation of the self-sensing properties of the material. Cyclic compressive load was conducted and the response to the piezoresistive properties of the nano composite was tested. It was observed that 0.1% of these carbon nano materials had better electrical properties.

A comparative study of different metal oxide nanoparticles dispersed PVDF/PEO blend matrix-based advanced multifunctional nanodielectrics for flexible electronic devices

Polymer nanocomposites (PNCs) are technologically smart multifunctional, flexible, and stretchable-type materials of high scientific and industrial interest. In this study, PNC films based on host polymer matrix of poly(vinylidene difluoride) (PVDF) blended with poly(ethylene oxide) (PEO) (compositional ratio PVDF/PEO = 75/25 wt/wt%) and 5 wt% different metal oxide nanoparticles (i.e., Al2O3, SnO2, TiO2, and ZnO) as nanoinclusions have been developed by casting from solution. These films were characterized with advanced techniques namely; SEM, EDX, XRD, FTIR, DRS, and UV–vis spectroscopy for confirmation of their technological applications. The results evidence that these metal oxide nanoparticles produce significant alterations in the polymers spherulitic morphology, creates a large number of micro- to nano-sized pores, lowers the β-phase content of the PVDF and crystalline phase of PEO, and also the degree of crystallinity of the host matrix. Among these metal oxides, the Al2O3 nanoparticles considerably enhance the dielectric permittivity while other nanofillers anomalously alter the dielectric polarization processes and MWS relaxation of the PNC films in the frequency range 20 Hz – 1 MHz at ambient temperature. AC electrical conduction is found relatively high for the Al2O3 and low for ZnO nanoparticles containing PNC films. The optical energy bandgap of these PNC films are sturdily ruled by the characteristic optical properties of the nanofillers. The physical, morphological, structural, dielectric, and optical parameters of these metal oxide nanofillers are considered for the demonstration of relative changes in the investigated properties of the PNC materials. Experimental results evidence multifunctionality of these PNC materials to be used as controllable nanodielectrics for the development of flexible-type macro- and microelectronic devices in the advances of porous membrane technology, UV-shielders, and the optical bandgap tuners.