Tunable Architecture Research Articles

Hollow NiCo2S4 Nanospheres Hybridized with 3D Hierarchical Porous rGO/Fe2O3 Composites toward High‐Performance Energy Storage Device

AbstractHierarchical hollow NiCo2S4 microspheres with a tunable interior architecture are synthesized by a facile and cost‐effective hydrothermal method, and used as a cathode material. A three‐dimensional (3D) porous reduced graphene oxide/Fe2O3 composite (rGO/Fe2O3) with precisely controlled particle size and morphology is successfully prepared through a scalable facile approach, with well‐dispersed Fe2O3 nanoparticles decorating the surface of rGO sheets. The fixed Fe2O3 nanoparticles in graphene efficiently prevent the intermediates during the redox reaction from dissolving into the electrolyte, resulting in long cycle life. KOH activation of the rGO/Fe2O3 composite is conducted for the preparation of an activated carbon material–based hybrid to transform into a 3D porous carbon material–based hybrid. An energy storage device consisting of hollow NiCo2S4 microspheres as the positive electrode, the 3D porous rGO/Fe2O3 composite as the negative electrode, and KOH solution as the electrolyte with a maximum energy density of 61.7 W h kg−1 is achieved owing to its wide operating voltage range of 0–1.75 V and the designed 3D structure. Moreover, the device exhibits a high power density of 22 kW kg−1 and a long cycle life with 90% retention after 1000 cycles at the current density of 1 A g−1.

Graphene Quantum Dots-Driven Multiform Morphologies of β-NaYF4:Gd3+/Tb3+ Phosphors: The Underlying Mechanism and Their Optical Properties.

Dimension and shape tunable architectures of inorganic crystals are of extreme interest because of morphology-dependent modulation of the properties of the materials. Herein, for the first time, we present a novel impurity-driven strategy where we studied the influence of in situ incorporation of graphene quantum dots (GQDs) on the growth of β-NaYF4:Gd3+/Tb3+ phosphor crystals via a hydrothermal route. The GQDs function as a nucleation site and by changing the concentration of GQDs, the morphology of β-NaYF4:Gd3+/Tb3+ phosphors was changed from rod to flowerlike structure to disklike structure, without phase transformation. The influence of size and functionalization of GQDs on the size and shape of phosphor crystals were also systematically studied and discussed. Plausible mechanisms of formation of multiform morphologies are proposed based on the heterogeneous nucleation and growth. Most interestingly, the experimental results indicate that the photoluminescence properties of β-NaYF4:Gd3+/Tb3+ phosphor crystals are strongly dependent on the crystallite size and morphology. This study would be suggestive for the precisely controlled growth of inorganic crystals; consequently, it will open new avenues and thus may possess potential applications in the field of materials and biological sciences.

Effect of Binder Architecture on the Performance of Silicon/Graphite Composite Anodes for Lithium Ion Batteries.

Although significant progress has been made in improving cycling performance of silicon-based electrodes, few studies have been performed on the architecture effect on polymer binder performance for lithium-ion batteries. A systematic study on the relationship between polymer architectures and binder performance is especially useful in designing synthetic polymer binders. Herein, a graft block copolymer with readily tunable architecture parameters is synthesized and tested as the polymer binder for the high-mass loading silicon (15 wt %)/graphite (73 wt %) composite electrode (active materials >2.5 mg/cm2). With the same chemical composition and functional group ratio, the graft block copolymer reveals improved cycling performance in both capacity retention (495 mAh/g vs 356 mAh/g at 100th cycle) and Coulombic efficiency (90.3% vs 88.1% at first cycle) than the physical mixing of glycol chitosan (GC) and lithium polyacrylate (LiPAA). Galvanostatic results also demonstrate the significant impacts of different architecture parameters of graft copolymers, including grafting density and side chain length, on their ultimate binder performance. By simply changing the side chain length of GC-g-LiPAA, the retaining delithiation capacity after 100 cycles varies from 347 mAh/g to 495 mAh/g.

Energy Efficient Quality Tunable CORDIC for DSP Applications on Battery Operated Portable Devices

COrdinate Rotation DIgital Computer (CORDIC) is commonly utilized for the computation of cosine/sine i.e., the trigonometric functions, singular value decomposition, in digital signal processing (especially in image/video processing), etc. This paper introduces an energy efficient quality tunable CORDIC architecture that computes the cosine/sine values of any required angle in real-time, and is thus well suited for real time DSP applications, especially for image or video processing applications. The proposed architecture reduces the latency and overcomes data dependency by simultaneously performing all the five iterations, that may vary depending upon the desired energy efficiency. The novelty of this architecture is that, desired quality can be achieved by selecting one out of the available three modes. In order to assess the efficacy of the suggested architecture, some benchmark images are processed using the Discrete Cosine Transform (DCT) coefficients obtained via the proposed design. Energy saving is achieved at the cost of slight acceptable degradation in the output image quality. Further, the simulation results show that the proposed architecture is 92.3%, 2.8% and 49.08% more energy efficient than the existing basic, scale-free and lookahead CORDIC architectures, respectively.

Designer biomaterials for mechanobiology.

Biomaterials engineered with specific bioactive ligands, tunable mechanical properties and complex architecture have emerged as powerful tools to probe cell sensing and response to physical properties of their material surroundings, and ultimately provide designer approaches to control cell function.

Reflectionless Adaptive RF Filters: Bandpass, Bandstop, and Cascade Designs

A class of frequency-reconfigurable input-reflectionless/absorptive RF/microwave filters is presented. They consist of tunable complementary-duplexer architectures that are composed of a main and an auxiliary channel with opposite filtering transfer functions. By loading the auxiliary channel with a reference-impedance resistor and by taking the output node of the main channel as the output terminal of the overall circuit, a filtering network of the same type of the main channel with theoretically perfect input-reflectionless behavior at all frequencies can be realized. This technique can be applied to design spectrally agile completely input-reflectionless filters with any kind of transfer function, such as low-pass, high-pass, and single/multiband bandpass/bandstop filters. The theoretical analysis of the first-order absorptive bandpass/bandstop filtering sections based on a coupling-matrix formulation is detailed. Furthermore, the synthesis of high-selectivity reflectionless filters either by cascading multiple first-order cells or using high-order channels in a single complementary duplexer is also described. For practical-demonstration purposes, frequency-tunable lumped-element and microstrip prototypes are manufactured and characterized. They correspond to first- and second-order bandpass/bandstop filters. In addition, their in-series cascade connection is used to implement a bandpass filter with spectrally controllable passband and out-of-band notches.

Two Tunable Frequency Duplexer Architectures for Cellular Transceivers

In this paper, two architectures for tunable duplexers are presented. The tuning is accomplished through variable capacitance and resistance. The architectures are based on a three element series-parallel resonator, with one pass and one stop frequency. Both architectures rely on filtering as well as cancellation for good Tx to Rx isolation while maintaining low insertion loss. The first architecture, the filtered transformer balanced (FTB) isolator, has single ended transmit and antenna ports and a differential receive port. The second architecture, the cross coupled filtering (CCF) isolator, is fully differential. For a resonator $Q$ of 50, the impedance ratio of the resonator at pass and stop frequencies is 18.5 dB for 3GPP band-I. In the FTB isolator, this results in 1.65-dB Tx and 2.14-dB Rx insertion loss, and 53 dB isolation for a 20-MHz channel bandwidth. In the CCF isolator, this results in 1.9-dB Tx and 1.9-dB Rx insertion loss, and 59-dB isolation for a 20-MHz channel bandwidth. These figures are obtained with a 20% resistive mismatch, showing feasibility of good performance in an environment with changing impedance. As the operating frequencies of cellular systems increase, these structures will become fully integratable due to the reduced sizes of inductors and transformers.

Fast Setting Silk Fibroin Bioink for Bioprinting of Patient‐Specific Memory‐Shape Implants

The pursuit for the "perfect" biomimetic and personalized implant for musculoskeletal tissue regeneration remains a big challenge. 3D printing technology that makes use of a novel and promising biomaterials can be part of the solution. In this study, a fast setting enzymatic-crosslinked silk fibroin (SF) bioink for 3D bioprinting is developed. Their properties are fine-tuned and different structures with good resolution, reproducibility, and reliability can be fabricated. Many potential applications exist for the SF bioinks including 3D bioprinted scaffolds and patient-specific implants exhibiting unique characteristics such as good mechanical properties, memory-shape feature, suitable degradation, and tunable pore architecture and morphology.

Metal-organic framework-derived Ni–Co alloy@carbon microspheres as high-performance counter electrode catalysts for dye-sensitized solar cells

Spherical-structured nano-/micromaterials with tunable shell architectures and compositions are becoming increasingly important and attractive for electrochemical energy conversion and storage. Herein, we report the synthesis of novel Ni–Co alloy@carbon microspheres by calcining Co/Ni bimetallic metal-organic frameworks (MOFs) prepared by a facile solvothermal reaction. Their structures, dimensions and electrochemical performance can be optimized by simply tuning the Co/Ni molar ratio. Benefiting from the advantageous structural and compositional features, the obtained Ni–Co alloy@carbon microspheres display exceptional electrochemical performance when used as counter electrode (CE) catalysts for dye-sensitized solar cells (DSSCs). In particular, the optimized NiCo0.2@C CE delivers an impressive power conversion efficiency (PCE) of 9.30%, showing a ∼15.7% enhancement compared to that of Pt CE (8.04%). Additionally, the NiCo0.2@C CE also demonstrates a good long-term electrochemical stability for the I3−/I− electrolyte. This work may provide new options for the design and preparation of efficient electrocatalysts with novel morphologies and desirable compositions.

Hydrophobic Coatings by Thiol-Ene Click Functionalization of Silsesquioxanes with Tunable Architecture.

The hydrolysis-condensation of trialkoxysilanes under strictly controlled conditions allows the production of silsesquioxanes (SSQs) with tunable size and architecture ranging from ladder to cage-like structures. These nano-objects can serve as building blocks for the preparation of hybrid organic/inorganic materials with selected properties. The SSQs growth can be tuned by simply controlling the reaction duration in the in situ water production route (ISWP), where the kinetics of the esterification reaction between carboxylic acids and alcohols rules out the extent of organosilane hydrolysis-condensation. Tunable SSQs with thiol functionalities (SH-NBBs) are suitable for further modification by exploiting the simple thiol-ene click reaction, thus allowing for modifying the wettability properties of derived coatings. In this paper, coatings were prepared from SH-NBBs with different architecture onto cotton fabrics and paper, and further functionalized with long alkyl chains by means of initiator-free UV-induced thiol-ene coupling with 1-decene (C10) and 1-tetradecene (C14). The coatings appeared to homogeneously cover the natural fibers and imparted a multi-scale roughness that was not affected by the click functionalization step. The two-step functionalization of cotton and paper warrants a stable highly hydrophobic character to the surface of natural materials that, in perspective, suggests a possible application in filtration devices for oil-water separation. Furthermore, the purification of SH-NBBs from ISWP by-products was possible during the coating process, and this step allowed for the fast, initiator-free, click-coupling of purified NBBs with C10 and C14 in solution with a nearly quantitative yield. Therefore, this approach is an alternative route to get sol-gel-derived, ladder-like, and cage-like SSQs functionalized with long alkyl chains.

Modular flow chamber for engineering bone marrow architecture and function.

The bone marrow is a soft, spongy, gelatinous tissue found in the hollow cavities of flat and long bones that support hematopoiesis in order to maintain the physiologic turnover of all blood cells. Silk fibroin, derived from Bombyx mori silkworm cocoons, is a promising biomaterial for bone marrow engineering, because of its tunable architecture and mechanical properties, the capacity of incorporating labile compounds without loss of bioactivity and demonstrated ability to support blood cell formation. In this study, we developed a bone marrow scaffold consisting of a modular flow chamber made of polydimethylsiloxane, holding a silk sponge, prepared with salt leaching methods and functionalized with extracellular matrix components. The silk sponge was able to support efficient platelet formation when megakaryocytes were seeded in the system. Perfusion of the chamber allowed the recovery of functional platelets based on multiple activation tests. Further, inhibition of AKT signaling molecule, which has been shown to be crucial in regulating physiologic platelet formation, significantly reduced the number of collected platelets, suggesting the applicability of this tissue model for evaluation of the effects of bone marrow exposure to compounds that may affect platelet formation. In conclusion, we have bioengineered a novel modular system that, along with multi-porous silk sponges, can provide a useful technology for reproducing a simplified bone marrow scaffold for blood cell production exvivo.

Biomimetic Architectured Graphene Aerogel with Exceptional Strength and Resilience.

Materials combining lightweight, robust mechanical performances, and multifunctionality are highly desirable for engineering applications. Graphene aerogels have emerged as attractive candidates. Despite recent progresses, the bottleneck remains how to simultaneously achieve both strength and resilience. While multiscale architecture designs may offer a possible route, the difficulty lies in the lack of design guidelines and how to experimentally achieve the necessary structure control over multiple length scales. The latter is even more challenging when manufacturing scalability is taken into account. The Thalia dealbata stem is a naturally porous material that is lightweight, strong, and resilient, owing to its architecture with three-dimensional (3D) interconnected lamellar layers. Inspired by such, we assemble graphene oxide (GO) sheets into a similar architecture using a bidirectional freezing technique. Subsequent freeze-drying and thermal reduction results in graphene aerogels with highly tunable 3D architectures, consequently an unusual combination of strength and resilience. With their additional electrical conductivity, these graphene aerogels are potentially useful for mechanically switchable electronics. Beyond such, our study establishes bidirectional freezing as a general method to achieve multiscale architectural control in a scalable manner that can be extended to many other material systems.

Carbon coated anatase TiO 2 mesocrystals enabling ultrastable and robust sodium storage

Abstract Nanoporous anatase TiO 2 mesocrystals with tunable architectures and crystalline phases were successfully fabricated in the presence of the butyl oleate and oleylamine. Especially, the introduced surfactants served as a carbon source, bring a uniform carbon layer (about 2–8 nm) for heightening the electronic conductivity. The carbon coated TiO 2 mesocrystals assembled from crystalline tiny subunits have more space sites for sodium-ion storage. When the material was applied as an electrode material in rechargeable sodium-ion batteries, it exhibited a superior capacity of about 90 mA h g −1 at 20 C (1 C = 168 mA g −1 ) and a highly reversible capacity for 5000 cycles, which is the longest cycle life reported for sodium storage in TiO 2 electrodes.

Photomanipulated Architecture and Patterning of Azopolymer Array.

Here reported is the approach to prepare the tunable 3D architecture and patterning through photoinduced orientation of azopolymer. The hemispherical PAzoMA array can be transformed into spindlelike, flat ellipsoidlike, thick spindlelike, near-hexagon, near-quadrangle, and near-rhombus arrays while being exposed to linearly polarized light (LPL). The size and alignment of the arrays can be precisely controlled by manipulating the irradiation time. Furthermore, complex 3D architectures of the PAzoMA array are readily fabricated through secondary irradiation along different direction. This technique is promising for functionalized surfaces and photonic devices.

Hollow nickel-aluminium-manganese layered triple hydroxide nanospheres with tunable architecture for supercapacitor application

Hollow triple layered Ni-Al-Mn hydroxide nanocomposite is a promising electrode material with high capacitance value. Moreover, the material provides a high energy density with good cycling stability. Here we demonstrate the facile method for preparation of hollow layered triple hydroxide material in a combination of Nickel, Aluminium and Manganese with high surface area and mesoporous nature. Owing to its high electrode area and fast electron-ion transfer nature, the hollow Ni-Al-Mn hydroxide exhibits the high capacitance of 1756 F/g at 4 A/g and retains its capacitance value upto 89.5% of initial values after 4000 cycles. Additionally, it provides a higher energy density of 239.0795 Wh/kg at a power density of 1980 W/kg. HLTH of Ni-Al-Mn nanocomposite provides a better capacitance effect. Finally, this material provides a general approach for designing supercapacitor with tunable nanostructure and enhanced supercapacitor behaviour has a large application in energy storage and conversion devices.

Physical Mechanism Behind Enhanced Photoelectrochemical and Photocatalytic Properties of Superhydrophilic Assemblies of 3D-TiO2 Microspheres with Arrays of Oriented, Single-Crystalline TiO2 Nanowires as Building Blocks Deposited on Fluorine-Doped Tin Oxide.

In comparison to the one-dimensional (1D) semiconductor nanostructures, the hierarchical, three-dimensional (3D) microstructures, composed of the arrays of 1D nanostructures as building blocks, show quite unique physicochemical properties due to efficient photon capture and enhanced surface to volume ratio, which aid in advancing the performance of various optoelectronic devices. In this contribution, we report the fabrication of surfactant-free, radially assembled, 3D titania (rutile-phase) microsphere arrays (3D-TMSAs) composed of bundles of single-crystalline titania nanowires (NWs) directly on fluorine-doped conducting oxide (FTO) substrates with tunable architecture. The effects of growth parameters on the morphology of the 3D-TMSAs have been studied thoroughly. The 3D-TMSAs grown on the FTO-substrate showed superior photon-harvesting owing to the increase in light-scattering. The photocatalytic and photon to electron conversion efficiency of dye-sensitized solar cells (DSSC), where the optimized 3D-TMSAs were used as an anode, showed around 44% increase in the photoconversion efficiency compared to that of Degussa P-25 as a result of the synergistic effect of higher surface area and enhanced photon scattering probability. The TMSA film showed superhydrophilicity without any prior UV irradiation. In addition, the presence of bundles of almost parallel NWs led to the formation of arrays of microcapacitors, which showed stable dielectric performance. The fabrication of single-crystalline, oriented, self-assembled TMSAs with bundles of titania nanowires as their building blocks deposited on transparent conducting oxide (TCO) substrates has vast potential in the area of photoelectrochemical research.

Elaboration and evaluation of alginate foam scaffolds for soft tissue engineering

Controlling microarchitecture in polymer scaffolds is a priority in material design for soft tissue applications. This paper reports for the first time the elaboration of alginate foam-based scaffolds for mesenchymal stem cell (MSC) delivery and a comparative study of various surfactants on the final device performance. The use of surfactants permitted to obtain highly interconnected porous scaffolds with tunable pore size on surface and in cross-section. Their mechanical properties in compression appeared to be adapted to soft tissue engineering. Scaffold structures could sustain MSC proliferation over 14 days. Paracrine activity of scaffold-seeded MSCs varied with the scaffold structure and growth factors release was globally improved in comparison with control alginate scaffolds. Our results provide evidence that exploiting different surfactant types for alginate foam preparation could be an original method to obtain biocompatible scaffolds with tunable architecture for soft tissue engineering.

Development of a thermosensitive HAMA-containing bio-ink for the fabrication of composite cartilage repair constructs

Fine-tuning of bio-ink composition and material processing parameters is crucial for the development of biomechanically relevant cartilage constructs. This study aims to design and develop cartilage constructs with tunable internal architectures and relevant mechanical properties. More specifically, the potential of methacrylated hyaluronic acid (HAMA) added to thermosensitive hydrogels composed of methacrylated poly[N-(2-hydroxypropyl)methacrylamide mono/dilactate] (pHPMA-lac)/polyethylene glycol (PEG) triblock copolymers, to optimize cartilage-like tissue formation by embedded chondrocytes, and enhance printability was explored. Additionally, co-printing with polycaprolactone (PCL) was performed for mechanical reinforcement. Chondrocyte-laden hydrogels composed of pHPMA-lac-PEG and different concentrations of HAMA (0%–1% w/w) were cultured for 28 d in vitro and subsequently evaluated for the presence of cartilage-like matrix. Young’s moduli were determined for hydrogels with the different HAMA concentrations. Additionally, hydrogel/PCL constructs with different internal architectures were co-printed and analyzed for their mechanical properties. The results of this study demonstrated a dose-dependent effect of HAMA concentration on cartilage matrix synthesis by chondrocytes. Glycosaminoglycan (GAG) and collagen type II content increased with intermediate HAMA concentrations (0.25%–0.5%) compared to HAMA-free controls, while a relatively high HAMA concentration (1%) resulted in increased fibrocartilage formation. Young’s moduli of generated hydrogel constructs ranged from 14 to 31 kPa and increased with increasing HAMA concentration. The pHPMA-lac-PEG hydrogels with 0.5% HAMA were found to be optimal for cartilage-like tissue formation. Therefore, this hydrogel system was co-printed with PCL to generate porous or solid constructs with different mesh sizes. Young’s moduli of these composite constructs were in the range of native cartilage (3.5–4.6 MPa). Interestingly, the co-printing procedure influenced the mechanical properties of the final constructs. These findings are relevant for future bio-ink development, as they demonstrate the importance of selecting proper HAMA concentrations, as well as appropriate print settings and construct designs for optimal cartilage matrix deposition and final mechanical properties of constructs, respectively.

PEG-Induced Synthesis of Coordination-Polymer Isomers with Tunable Architectures and Iodine Capture.

Controllable synthesis of coordination polymer (CP) isomers and revealing their structure-property relationships remain enormous challenges. Three new supramolecular isomers have been synthesized by tuning the poly(ethylene glycol) (PEG) content in the feed. These supramolecular isomers have the same framework formula of [Cu2 I2 (tppe)] and different architectures from the classical 2D stacking framework to a 3D entangled system with the coexistence of interpenetration and polycatenation, and a 3D topological framework. Interestingly, these CPs could be utilized for capturing iodine molecules. According to multiple complementary experiments and crystallographic analyses, iodine capture is mainly based on halogen-bond interactions in the inorganic {Cu2 I2 } building blocks of the framework. The present study describes a structure-property relationship in supramolecular isomerism with distinct topological structures.

Watt-Level mm-Wave Power Amplification With Dynamic Load Modulation in a SiGe HBT Digital Power Amplifier

Performance limits and design techniques for Watt-level power amplification at millimeter-wave (mm-wave) frequencies using silicon germanium (SiGe) HBT Class-E power amplifiers (PAs) is presented in this paper. A Class-E power modulator architecture is proposed for demonstrating highspeed data transmission using ASK modulation at mm-wave frequencies. Several of these 1-b power modulators are power combined to realize a Watt-level digital PA with several levels of output amplitude at mm-wave frequencies. A dynamic load modulation concept is proposed to mitigate the effect of load pulling in the digital PA at power back-off. A tunable transmission line architecture with variable characteristic impedance is proposed to realize this dynamic load modulation network and enable efficiency enhancement at power back-off levels in the Watt-level digital PA. Watt-level power generation at mm-waves was demonstrated in a eight-way combined digital PA with dynamic load modulation, fabricated in a 0.13-μm SiGe BiCMOS process with ≈29 dBm (0.8 W) measured output power at 46 GHz, 18.4% peak power-added-efficiency, and 60% of the peak efficiency at 6-dB power back-off.