Tunable Mechanism Research Articles

Tungsten disulfide (WS2) doped polyacrylamide (PAAm) composites: Gelation and optical studies

The organic Acrylamide (AAm) copolymerization in various contents of inorganic WS2 has been reported. The aim was to investigate the effect of the WS2 amount on the obtained morphology and the gelation process of the AAm composites. It was found that during gelation process the photon intensity of transmission decreased significantly above some critical time, called the gel point, tg. The decrease in the photon intensity of transmission was related to the increase in the intensity of scattered light from the gel attributable to the production of microgel that occurs while copolymerization held in AAm with Bis-Acrylamide (BIS). Gel points were found to be increased by increasing WS2 content. Time-dependent scattering of composites manifests the growth mechanism, the greater microgel particles, as in agreement with Rayleigh’s equation of scattering. It is determined that concentration of microgels is inversely proportional to the WS2 content. The composite rate constants of gelation, kr were produced and observed that it is proportional to WS2 content. It is understood that inclusion of WS2 in AAm system during gelation delays the process at early times but then contributes to increase the gelation process by increasing the rate of polymerization. Besides less compact PAAm gels are produced in the presence of WS2 atoms. It is also shown that the microgel growth mechanism and gel point of PAAm composite incorporated with WS2 can be significantly tailored by the amount of WS2. Tunable growth mechanism and critical gelation point is crucial for flexible electronic applications.

Cubic-like In2O3/α-Fe2O3 heterostructures assembled with 2D porous nanoplates for superior triethylamine gas-sensing behavior

Cubic-like In2O3/α-Fe2O3 heterostructures assembled with 2D porous nanoplates have been prepared by solvothermal method and subsequent calcination process. The introduction of Fe3+ component plays an important role for the morphological evolution of In2O3-based samples with unique crystal nucleation and growth mechanism. Compared with flower-like In2O3 self-assemblies composed of tower-like structural units, In2O3/α-Fe2O3 composites can display superior trimethylamine (TEA) gas-sensing behavior. For example, the optimal working temperature is reduced from 250 to 170 °C, and the response value of In/Fe-2 materials is 375.43, which is about 6.23 times than that of In2O3 sensors. The enhanced gas-sensing properties are mainly attributed to large specific surface area (234.4 m2/g), the effective In2O3-α-Fe2O3 heterojunctions, unique surface/interface effects, and tunable electron transmission mechanism.

Study on the color tunability and energy transfer mechanism in Tm3+/Dy3+ co-doped LiLaSiO4 phosphors

Many color-tunable LiLaSiO4: αTm3+, βDy3+ phosphors were prepared using the traditional high-temperature solid-phase method. The phase composition, surface morphology, fluorescence spectrum, fluorescence lifetime, energy transfer mechanism, and color coordinates of the samples were analyzed using XRD, SEM, TEM and fluorescence spectrometer. The results show that LiLaSiO4: αTm3+ phosphor emits high intensity blue light at 460 nm and the concentration quenching point of Tm3+, α = 0.015 mol. In LiLaSiO4: αTm3+, βDy3+ phosphors, as the doped Dy3+ doping increases, the luminescence intensity of Tm3+ gradually decreases, the luminescence intensity of Dy3+ first increases and then decreases. The concentration quenching point of Dy3+, β = 0.015 mol. Adjustable light-emitting color can be obtained by changing the doping molar mass of Dy3+ or the wavelength of the excitation light. There is an effective energy transfer between Tm3+→Dy3+. The energy transfer mechanism is the electric dipole-electric dipole interaction, and the energy transfer efficiency reaches 90.11% when β = 0.06 mol. The quantum yield of LiLaSiO4:0.015 Tm3+,0.015Dy3+ was 39.0%. The single-matrix white light LiLaSiO4: αTm3+, βDy3+ phosphors with excellent performance is a prospective material for of white LEDs.

Stimulation Modulates Adhesion and Mechanics of Hydrogel Adhesives.

The ability to modulate the adhesion of soft materials on-demand is desired for broad applications ranging from tissue repair to soft robotics. Research effort has been focused on the chemistry and architecture of interfaces, leaving the mechanics of soft adhesives overlooked. Stimuli-responsive mechanisms of smart hydrogels could be leveraged for achieving stimuli-responsive hydrogel adhesives that respond mechanically to external stimuli. Such stimuli-responsive hydrogel adhesives involve complex chemomechanical coupling and interfacial fracture phenomena, calling for mechanistic understanding to enable rational design. Here, we combine experimental, computational, and analytical approaches to study a thermo-responsive hydrogel adhesive. Experimentally, we show that the adhesion and mechanical properties of a stimuli-responsive hydrogel adhesive are both enhanced by the application of a stimulus. Our analysis further reveals that the enhanced adhesion stems from the increased fracture energy of the bulk hydrogel and the insignificant residual stress on the adhesive-tissue interface. This study presents a framework for designing stimuli-responsive hydrogel adhesives based on the modulation of bulk properties and sheds light on the development of smart adhesives with tunable mechanics.

A tunable phononic crystal system for elastic ultrasonic wave control

Tunable phononic crystals (PCs) are burgeoning within the engineering communities due to their adjustable capabilities for manipulating elastic waves. In this Letter, a shape memory alloy (SMA) stubbed PC is elaborated to achieve the tunable bandgaps for the control of ultrasonic waves. The tunable mechanism stems from the phase transformation of the SMA between the martensite at low temperature and the austenite at high temperature. Both numerical modeling and experimental verification are conducted to validate the achievement of the controllable stop band properties. The proposed SMA PC design could be broadened to numerous promising applications, e.g., ultrasonic wave waveguiding, flat-lens focusing, and mechanical frequency filtering, possessing enabling potential for highly adjustable wave manipulation.

Widely tunable silicon Raman laser

Stimulated Raman scattering is an effective means of wavelength conversion and can largely extend the operating spectral range of an optical source. We demonstrate a high-performance tunable Raman laser on a sub-micrometer-thick silicon on insulator wafer using a standard foundry process. The key feature to this laser is the use of a tunable coupling mechanism to adjust both pump and signal coupling coefficients in the ring cavity, allowing demonstration of laser emission over a large wavelength tuning range of 83 nm. This Raman laser demonstrates efficient (slope of up to 26% and a maximum pump-to-signal power conversion efficiency of 10%) on-chip nonlinear wavelength conversion. Our results indicate great promise for substantially increasing the optical spectral resources available on a silicon chip.

Improvement of a Tunable Stiffness Organ-Grasping Device by Design of a Wavy-Shaped Beam Structure

Tunable stiffness mechanisms can increase the noninvasiveness and stability of organ manipulation in laparoscopic liver resection. We have developed an organ-grasping device using beam-shaped tunable stiffness mechanism. Increasing the change ratio of stiffness will improve the performance of the device by offering high flexibility when adhering to the liver surface and high rigidity during the manipulation of the liver; however, optimal design of the beam has not been investigated. In this study, we investigate the wavy structure shape of the device that enhances the change in the ratio of stiffness. To increase the stiffness in a high-stiffness state, we used principal stress lines in the device to design the edge curve of the wavy shape material in the beams. We also investigated the arrangement of the wavy shape to decrease the stiffness in a low-stiffness state. Simulation using finite element method showed that the change ratio of stiffness was improved up to 13.0 by the new wavy shape arranged with the uniformly thick bottom of the waves.

Graphene-integrated hybridized metamaterials for wide-angle tunable THz absorbers

Metamaterial absorbers with excellent absorption properties and real-time tunability are desirable for practical applications. In this paper, we design and numerically investigate a polarization insensitive wide-angle metamaterial absorber with tunable absorption strength formed by finite-length symmetric metallic plates and graphene sheet. This structure achieves a near perfect absorption, and remains highly absorptive with wide incident-angle, higher than 80% at 60o for TE mode and around 90% at 70o for TM mode. Absorption strength can be varied between 97% and 52% by controlling the Fermi energy of graphene while the operating frequency remains relatively stable. Also without the presence of a ground plane as in other conventional absorbers, waves outside of the absorption band are allowed to travel through. The absorbing principle and absorption tunability mechanism are elucidated using effective medium analysis and finite integration simulations.

Programmable Self‐Locking Micromachines with Tunable Couplings

Intelligent micromachines that perform tasks in complex microenvironments by adjusting structural configurations and physical properties offer substantial potential for use in many fields, including precision medicine, microfluidic channels, micromanipulations, and bioengineering. Recent progress in smart materials and 4D microprinting provides a feasible strategy for fabricating compound micromachines by designing and assembling predictable 3D‐to‐3D shape‐morphing components. However, shape transformations of these components can only be triggered simultaneously by external stimuli, and orderly triggering among them cannot be achieved yet for an intended purpose of performing more efficient actions. Herein, a novel sequentially triggered strategy is proposed for developing intelligent micromachines that consist of multiple reconfigurable components that work interactively with each other. Furthermore, self‐locking micromachines with tunable coupling mechanisms that coordinate accurate time‐sequence deformations among components are achieved. Three types of locking couplings are modulated based on finite‐element analysis (FEA)‐aided design. The proposed method provides an effective strategy to create next‐generation intelligent micromachines that can change their shapes to adapt to complex situations and complete multiple tasks.

A 3D physio-mimetic interpenetrating network-based platform to decode the pro and anti-tumorigenic properties of cancer-associated fibroblasts

Three-dimensional (3D) biomaterials with physiologically relevant and experimentally tractable biomechanical features are important platforms to advance our understanding of the influence of tissue mechanics in disease progression. Herein, an interpenetrating network (IPN) of collagen and alginate 3D culture system with tunable extracellular microstructure and mechanics is exploited as a tumor stroma proxy to study phenotypic plasticity of colorectal cancer-associated fibroblasts (CAF). In combination with Next Generation Sequencing (NGS) data analysis, we demonstrated that tuning the storage modulus of the IPN hydrogel between 49 and 419 Pa can trigger a reversible switch between an inflammatory (i-state, α-SMAlowIL-6high) and myofibroblastic (m-state, α-SMAhighIL-6low) state in CAF that is dependent on the polymer network confinement effect and ROS-HIF1-α mechanotransduction signaling axis. Secretome from m-state CAF upregulated several epithelial-mesenchymal-transition (EMT) transcripts and induced robust scattering in DLD-1, HCT116, and SW480 human colorectal adenocarcinoma, while the EMT-inducing capacity is muted in i-state CAF, suggestive of an anti-tumorigenic role. Our findings were further validated through Gene Expression Profiling Interactive Analysis (GEPIA), which showed that cytokines secreted at higher levels by i-state CAF are correlated (p < 0.05) with good overall colorectal cancer patient survival. Therefore, 3D network density and spatial cellular confinement are critical biophysical determinants that can profoundly influence CAF states, paracrine signaling, and EMT-inducing potential. Statement of significanceThe communication between cancer cells and cancer-associated fibroblasts (CAF) contributes to tumor metastasis. CAF represent a diverse population of cellular subsets that can either promote or restrain tumor progression. However, the origin and cause of CAF heterogeneity remain elusive, limiting CAF-directed therapies for clinical use. We studied the dynamic phenotypes of CAF using a 3D physio-mimetic culture platform consisting of an interpenetrating collagen-alginate network. Combined with transcriptomic stratification and correlative analysis using cancer patient dataset, we showed phenotypic interconversion between inflammatory and myofibroblastic states, with anti- and pro-tumorigenic functions, in human colorectal CAF. This multidisciplinary study reveals the functional diversity of colorectal CAF caused by biophysical cues. The finding will influence the development of new CAF biomarkers and cancer therapies.

Tunable terahertz Dirac semimetal metamaterials

The tunable propagation properties of 3D Dirac semimetal (DSM) patterned metamaterial (MM) structures have been symmetrically investigated in the terahertz (THz) regime. The results demonstrate that the resonant properties are very sensitive to the thicknesses of DSM MMs, and hundreds of nanometers are required to excite strong resonant curves. The DSM MMs support both strong LC and dipolar resonances, quite different from graphene MM patterns which mainly depend on dipolar resonance. As the Fermi level increases, the resonant strength becomes stronger, and significant modulation can be achieved, e.g. the amplitude and frequency modulation depths of transmission curves are more than 99% and 80%, respectively. In addition, by utilizing asymmetrical resonators, a very sharp Fano resonant peak is achieved with a large Q-factor of more than 25, for which the figure of merit is about 20. The results are very helpful to understand the tunable mechanisms of DSM devices and design novel THz plasmonic components, such as modulators, filters, and sensors.

Transport, functions, and interaction of calcium and manganese in plant organellar compartments.

Calcium (Ca2+) and manganese (Mn2+) are essential elements for plants and have similar ionic radii and binding coordination. They are assigned specific functions within organelles, but share many transport mechanisms to cross organellar membranes. Despite their points of interaction, those elements are usually investigated and reviewed separately. This review takes them out of this isolation. It highlights our current mechanistic understanding and points to open questions of their functions, their transport, and their interplay in the endoplasmic reticulum (ER), vesicular compartments (Golgi apparatus, trans-Golgi network, pre-vacuolar compartment), vacuoles, chloroplasts, mitochondria, and peroxisomes. Complex processes demanding these cations, such as Mn2+-dependent glycosylation or systemic Ca2+ signaling, are covered in some detail if they have not been reviewed recently or if recent findings add to current models. The function of Ca2+ as signaling agent released from organelles into the cytosol and within the organelles themselves is a recurrent theme of this review, again keeping the interference by Mn2+ in mind. The involvement of organellar channels [e.g. glutamate receptor-likes (GLR), cyclic nucleotide-gated channels (CNGC), mitochondrial conductivity units (MCU), and two-pore channel1 (TPC1)], transporters (e.g. natural resistance-associated macrophage proteins (NRAMP), Ca2+ exchangers (CAX), metal tolerance proteins (MTP), and bivalent cation transporters (BICAT)], and pumps [autoinhibited Ca2+-ATPases (ACA) and ER Ca2+-ATPases (ECA)] in the import and export of organellar Ca2+ and Mn2+ is scrutinized, whereby current controversial issues are pointed out. Mechanisms in animals and yeast are taken into account where they may provide a blueprint for processes in plants, in particular, with respect to tunable molecular mechanisms of Ca2+ versus Mn2+ selectivity.

Tunable low-frequency and broadband acoustic metamaterial absorber

Current sound-absorbing materials have fixed absorption spectra due to unalterable local resonance properties, which limit their application potential in many noise control scenarios. Clear motivation exists, therefore, to design an acoustic absorber to fit the actual noise spectrum with reconfigurable geometry and subwavelength thickness. Here, we analytically present and experimentally verify a tunable low-frequency acoustic absorber composed of multi-layered ring-shaped microslit tubes with a deep subwavelength thickness. This decreases the working frequency and significantly increases the acoustic absorption efficiency simultaneously. A physical model of the proposed metastructure is established on the basis of an acoustic equivalent circuit using microslit absorber theory. Superior impedance manipulation capability is achieved by rotating the middle microslit tube from 0° to 180°. This enables continuous tunability of the metamaterial absorber over a wide working frequency band. In both the simulated and measured results, highly efficient acoustic absorption (at least 0.9) is achieved in the range of 280–572 Hz. Simulations under oblique incidence are conducted to validate the wide-angle performance of the absorber. Based on the proposed tunable absorption mechanism, a hybrid metamaterial absorber is designed to produce adjustable broadband absorption with high efficiency. Our work helps pave the way to absorbing metamaterials being used in practical engineering applications such as noise control due to the advantages of tunable functionality, compactness, high efficiency, wide-angle absorption, and easy fabrication.

Multifunctional and Tunable Radar Absorber Based on Graphene‐Integrated Active Metasurface

AbstractIn this article, a multifunctional and tunable radar absorber which can achieve dynamical modulation of absorbing frequency, bandwidth, and amplitude is presented. Such a tunable radar absorber is composed of a graphene capacitor layer and an active metasurface layer. By controlling the impedance characteristic of each layer through the external bias voltages, the absorber not only can achieve the ultrawideband electromagnetic (EM) absorbing performance, but also can be switched to a narrowband absorption mode, and its absorption amplitude can be further adjusted at each of the above operation modes. Both simulated and experimental results have demonstrated that the −10‐dB reflection bandwidth ranging from 3.55 to 19.6 GHz can be realized, and the average reflection amplitude can be dynamically tuned between −3.8 and −11.5 dB. In addition, by changing the bias voltages, the absorber can also, respectively, switch its −10 dB reflection bandwidth to 3.5−11.1 GHz and 10.9−18.9 GHz, where the larger dynamic range of amplitude modulation is obtained. The equivalent circuit model is employed to explain the tunable absorption mechanism by analyzing the impedance matching characteristics. This hybrid design approach can effectively expand the EM reconfigurable functionalities of the current tunable absorber, which may further open a novel way of the graphene application in microwave frequencies.

Tuning the Active Sites of Atomically Thin Defective Bi12O17Cl2 via Incorporation of Subnanometer Clusters.

The introduction of subnanometer clusters as active sites on the surface of photocatalysts for efficiently tuning the selectivity and activity of the photocatalyts is still a challenge. Herein, the subnanometer Ag/AgCl clusters were incorporated on atomically thin defective Bi12O17Cl2 nanosheets via rebinding with unsaturated Cl atoms. Benefiting from the surficial Bi vacancies (VBi) and Bi-O vacancies (VBi-O) in this atomically thin architecture, the local atomic arrangement was tuned so that the subnanometer Ag/AgCl clusters were successfully incorporated. An enhancement of photocatalytic activity for NO removal was achieved in which the activity is 3 times higher than that of Bi12O17Cl2 and 1.8 times higher than that of defective Bi12O17Cl2. The substitution of the active sites from surficial VBi and VBi-O to be subnanometer Ag/AgCl clusters enables a tunable redox potential and different reaction mechanisms in NO removal. Moreover, the selectivity of the photoinduced redox reaction on NO oxidation and CO2 reduction was achieved via introducing an extra energy level.

Switchable dual-band to broadband terahertz metamaterial absorber incorporating a VO2 phase transition

We design and demonstrate a thermally switchable terahertz metamaterial absorber consisting of an array of orthogonal coupled split-ring metal resonators involving a VO2 phase transition. Numerical results indicate that the active metamaterial always absorbs the TE wave in dual-band regardless of insulating and metallic VO2, while the insulator-to-metal phase transition enables a switchable effect between dual-band and broadband absorption of the TM wave with the resonant frequency tunability of 33%. Especially under the metallic VO2 state, the absorption properties are polarization-dependent and exhibit a switching effect between dual-band and broadband absorption with the increase of the polarization angle. The tunable absorption mechanism can be explained by effective impedance theory and electric energy density distributions. The proposed dual-band to broadband metamaterial switching absorber may have broad applications in sensors, imaging and emitters.

Swaying gel: chemo-mechanical self-oscillation based on dynamic buckling

<h2>Summary</h2> Self-oscillating systems are powerful tools for transducing static energy inputs into repetitive motions without the aid of external control units. The challenge in sustaining the far-from-equilibrium motion of an oscillating material is to avoid the tendency of reaching thermodynamic equilibrium or get pinned at steady states in the dynamic process. While living organisms present elegant strategies in myriad self-oscillations (e.g<i>.</i>, peristalsis, cilia motion, homeostasis), current synthetic self-oscillating systems often rely on a fast actuation/reaction, to maintain the far-from-equilibrium motion, which prescribe highly specific chemical reactions and a material microstructure with limited stimuli and movement modes. Here, we present a dynamic buckling-based design for creating self-oscillating systems. The oscillation arises from the self-driven snap-through of a responsive hydrogel between bi-/multi-stable buckling configurations governed by a feedback loop. With broad choices of materials, tunable mechanics, and physical simplicity, this system opens a new venue for unlimited autonomous-oscillating materials applications.

ZIF-67-induced double-tubular 1D CeO2/Co3O4 heterostructures allowing electron transfer synergetic mechanism for enhanced photocatalytic performance

ZIF-67-induced double-tubular 1D CeO2/Co3O4 heterostructures have been prepared by an electrospinning method with tunable morphological evolution mechanism. As the adding amount of ZIF-67 increasing, the morphologies of CeO2-based nanomaterials are changed from porous granular nanobelt to smooth curly shape, and finally formed a double-tubular structure. The optimal CeO2/Co3O4 products consisting of well-dispersed double-tubular nanostructure with the external diameter of about 200 nm display high specific surface area of 196.05 m2g−1 and superior photocatalytic performance of methylene blue (MB). The rapid degradation rate of 97% within 40 min and high cycling stability without significant decrease of photocatalytic activity could be attributed to the unique electron transfer synergetic mechanism based on the combination of double-tubular microstructure and CeO2/Co3O4 heterojunctions.

Tunable 3D Dirac-semimetals supported mid-IR hybrid plasmonic waveguides.

Based on 3D Dirac-semimetal (DSM) modified hybrid waveguides, tunable propagation properties have been investigated, including the effects of Fermi levels, structural parameters, and operation frequency. The results show that if the operation frequency is smaller (larger) than the transition frequency (ℏω≈2|μc|), the proposed hybrid waveguides indicate strong (weak) confinement because the DSM layer manifests a high plasmonic (dielectric low) loss property. The dielectric fiber shape affects the propagation property obviously, as the elliptical parameter decreases, the confinement and figure of merit increase, and the loss reduces. With the increase in Fermi level, the propagation constant increases, and the frequency (amplitude) modulation depth is 32.31% (12.93%) if the Fermi level changes in the range of 0.01-0.15 eV. The results are very helpful in understanding the tunable mechanisms of hybrid waveguides and designing novel plasmonic devices in the future, e.g., modulators, filters, lasers, and resonators.

A Reconfigurable and Adjustable Compliance System for the Measurement of Interface Orthotic Properties.

A measurement system which provides INterface with Tunable Ergonomic properties using a Reconfigurable Framework with Adjustable Compliant Elements (INTERFACE system) is developed to implement the Rapid Evaluate and Adjust Device (READ) methodology. The geometry and stiffness of the Medial Longitudinal Arch (MLA) support provided by the INTERFACE system can be adjusted via linear actuators and tunable stiffness mechanisms, based on objective interface pressure/load distribution and subjective feedback evaluations. Validation tests were conducted on 13 subjects to measure the plantar pressure/load distribution and record the subjective feedback in different combinations of geometry and stiffness. The interface pressure/load distribution and subjective feedback of the support level indicate the efficacy of the adjustable geometry and stiffness. As the stiffness and geometrical height increased, the plantar loadings increased in the MLA region and decreased in the rear foot. Geometrical fitting can be achieved with the reconfigurable MLA support. The integration of locally adjustable stiffness makes it possible to fine tune the plantar pressure/load and provides the subjects with options of orthotic stiffness. The proposed INTERFACE system can be applied to conduct the measurement of the desired orthotic properties which satisfy the interface pressure/load requirement and the subject's comfort.