Aligned Structure Research Articles

RHMC: Modeling consistent information from deep multiple views via Regularized and Hybrid Multiview Coding

Modeling multiple views by unsupervised representation learning is a challenging problem, since multi-view data features are different from each other, and it is unclear how to perform representation learning to fully explore discriminative information from multiple views. Recent works focus on learning consistent information by contrasting high-dimensional features, but amounts of useful view-consistent information of low-dimensional representation is ignored, and such information can benefit the learned representation on downstream tasks. In this paper, we propose a novel method called Regularized and Hybrid Multiview Coding (RHMC) for comprehensively modeling consistent information between multiple views. We induce the discriminative improvement of features by constraining the learned multi-view representations in the latent space with diversified self-supervised learning tasks. Specifically, RHMC proposes a hybrid MI estimation, which jointly considers the mutual information between the aggregated high-dimensional feature and low-dimensional representation of views. RHMC enables the learned representation to model the consistent information that is hidden in low-dimensional representations under the direction of the aggregated high-dimensional feature. In hidden space, the problem of multi-view domain shift degenerates the performance of mutual information estimation. To tackle the issue, RHMC imposes globally aligned structures of the learned representations in the latent space, that is aligning the probability distribution of different views by utilizing the Wasserstein distance-based view alignment regularization. Empirically, our experimental validation supports the ability of RHMC to outperform the state-of-the-art self-supervised methods by a significant margin, which proves that RHMC can indeed model consistent and discriminative information from multi-view data.

An aligned fibrous and thermosensitive hyaluronic acid-puramatrix interpenetrating polymer network hydrogel with mechanical properties adjusted for neural tissue

Central nervous system (CNS) injuries such as stroke or trauma can lead to long-lasting disability, and there is no currently accepted treatment to regenerate functional CNS tissue after injury. Hydrogels can mimic the neural extracellular matrix by providing a suitable 3D structure and mechanical properties and have shown great promise in CNS tissue regeneration. Here we present successful synthesis of a thermosensitive hyaluronic acid-RADA 16 (Puramatrix™) peptide interpenetrating network (IPN) that can be applied in situ by injection.Thermosensitive hyaluronic acid (HA) was first synthesized by combining HA with poly(N-isopropylacrylamide). Then, the Puramatrix™ self-assembled peptide was combined with the thermosensitive HA to produce a series of injectable thermoresponsive IPNs. The HA-Puramatrix™ IPNs formed hydrogels successfully at physiological temperature. Characterization by SEM, rheological measurements, enzymatic degradation and swelling tests was performed to select the IPN optimized for neurologic use. SEM images of the optimized dry IPNs demonstrated an aligned porous structure, and the rheological measurements showed that the hydrogels were elastic, with an elastic modulus of approximately 500 Pa, similar to that of brain tissue. An evaluation of the cell–material interactions also showed that the IPN had biological characteristics required for tissue engineering, strongly suggesting that the IPN hydrogel possessed properties beneficial for regeneration of brain tissue.

Generation of a tendon-like tissue from human iPS cells

Tendons and ligaments are essential connective tissues that connect the muscle and bone. Their recovery from injuries is known to be poor, highlighting the crucial need for an effective therapy. A few reports have described the development of artificial ligaments with sufficient strength from human cells. In this study, we successfully generated a tendon-like tissue (bio-tendon) using human induced pluripotent stem cells (iPSCs). We first differentiated human iPSCs into mesenchymal stem cells (iPSC-MSCs) and transfected them with Mohawk (Mkx) to obtain Mkx-iPSC-MSCs, which were applied to a newly designed chamber with a mechanical stretch incubation system. The embedded Mkx-iPSC-MSCs created bio-tendons and exhibited an aligned extracellular matrix structure. Transplantation of the bio-tendons into a mouse Achilles tendon rupture model showed host-derived cell infiltration with improved histological score and biomechanical properties. Taken together, the bio-tendon generated in this study has potential clinical applications for tendon/ligament-related injuries and diseases.

Bio-inspired engineering of a perfusion culture platform for guided three-dimensional nerve cell growth and differentiation.

Collagen provides a promising environment for 3D nerve cell culture; however, the function of perfusion culture and cell-growth guidance is difficult to integrate into such an environment to promote cell growth. In this paper, we develop a bio-inspired design method for constructing a perfusion culture platform for guided nerve cell growth and differentiation in collagen. Based on the anatomical structure of peripheral neural tissue, a biomimetic porous structure (BPS) is fabricated by two-photon polymerization of IP-Visio. The micro-capillary effect is then utilized to facilitate the self-assembly of cell encapsulated collagen into the BPS. 3D perfusion culture can be rapidly implemented by inserting the cell-filled BPS into a pipette tip connected with syringe pumps. Furthermore, we investigate the nerve cell behavior in the BPS. 7-channel aligned cellular structures surrounded with a Schwann cell layer can be stably formed after a long-time perfusion culture. Differentiation of PC12 cells and mouse neural stem cells shows 3D neurite outgrowth alignment and elongation in collagen. The calcium activities of differentiated PC12 cells are visualized for confirming the preliminary formation of cell function. These results demonstrate that the proposed bio-inspired 3D cell culture platform with the advantages of miniaturization, structure complexity and perfusion has great potential for future application in the study of nerve regeneration and drug screening.

One Step Fabrication of Aligned Carbon Nanotube Sheet via FC‐CVD Technique

The rising need for lightweight and strong mechanical structures has contributed significantly towards the development of CNT macrostructures; however, the interplay of parameters and their discontinuous synthesis have obstructed their delivery to commercial level. Herein, floating catalyst chemical vapor deposition technique (FC‐CVD) has been employed for the fabrication of 90 cm long CNT sheet via continuous production of CNT aerogel. High degree of graphitization, thermal stability and purity have been indicated by Raman spectroscopy (IG/ID = 10.03), thermogravimetric analysis, and SEM studies. Continuous winding of CNT aerogel has increased the alignment into the sample which resulted into high electrical conductivity value of 21400 S/m. Furthermore, the alignment has been quantified by calculating optical anisotropic ratio via polarized Raman technique and conductivity anisotropic ratio κ‖ /κ⊥ which were calculated to be 4.63 and 3.4, respectively, and show reasonable agreement. These findings indicate that a well correlation of synthesis parameters results in highly aligned CNT sheet structure in a single step.

A highly aligned microgrid structure for wearable nanofibrous sensors with an enhanced sensitivity and detection range

Novel pressure sensing platform that features Ag/Ti3C2Tx (MXene)-modified grid-like polyurethane (PU) nanofibers was prepared sandwiched between the encapsulation layer and interdigital electrodes.

Anisotropic PLGA microsphere/PVA hydrogel composite with aligned macroporous structures for directed cell adhesion and proliferation

The fabrication of bio tissues using anisotropic constructs capable of repairing and/or replacing diseased bio tissues remains a significant challenge in tissue engineering. Therefore, this study investigated the fabrication of an anisotropic PLGA-microspheres/PVA-hydrogel composite using a novel directional freezing-thawing (DFT) technique. The DFT technique altered the properties of the anisotropic PLGA-microspheres/PVA-hydrogel composite, such that its compressive strength improved from 14.64 ± 1.09 MPa after three DFT cycles to 45.77 ± 6.73 MPa after nine cycles. The utilization of the DFT technique was also shown to enhance the proliferation and adhesion of cultured chondrocyte cells. The obtained results demonstrated that DFT constituted a facile method to fabricate anisotropic microsphere/hydrogel composites with improved and directed cell adhesion characteristics.

Biomimetic Aligned Micro-/Nanofibrous Composite Membranes with Ultrafast Water Transport and Evaporation for Efficient Indoor Humidification.

Humidifying membranes with ultrafast water transport and evaporation play a vital role in indoor humidification that improves personal comfort and industrial productivity in daily life. However, commercial nonwoven (NW) humidifying membranes show mediocre humidification capability owing to limited wicking capacity, low water absorption, and relatively less water evaporation. Herein, we report a biomimetic micro-/nanofibrous composite membrane with a highly aligned fibrous structure using a humidity-induced electrospinning technique for high-efficiency indoor humidification. Surface wettability and roughness are also tailored to achieve a high degree of superhydrophilicity by embedding hydrophilic silicon dioxide nanoparticles (SiO2 NPs) into the fiber matrix. The synergistic effect of the highly aligned fibrous structure and surface wettability endows composite membranes with ultrafast water transport and evaporation. Strikingly, the composite membrane exhibits an outstanding wicking height of 19.5 cm, a superior water absorption of 497.7%, a fast evaporation rate of 0.34 mL h-1, and a relatively low air pressure drop of 14.4 Pa, thereby achieving a remarkable humidification capacity of 514 mL h-1 (57% higher than the commercial NW humidifying membrane). The successful synthesis of this biomimetic micro-/nanofibrous composite membrane provides new insights into the development of micro-/nanofibrous humidifying membranes for personal health and comfort as well as industrial production.

Anisotropic electromagnetic wave absorption performance of Polyimide/multi-walled carbon nanotubes composite aerogels with aligned slit-like channels structure

Polyimide/carboxyl functionalized multi-walled carbon nanotubes (PI/MWCNTs-COOH) composite aerogels with aligned slit-like channels structure were synthesized through unidirectional freezing, freeze-drying and thermal imidization process in sequence. The composite aerogels with high porosity and low density exhibited highly aligned slit-like channels structure, which further imparted anisotropic electrical conductivity, electromagnetic wave absorption, and compression properties to the aerogels. PI/MWCNTs-COOH-16phr composite aerogel showed the minimum reflection loss (RLmin) of −52 dB at 12.8 GHz and effective absorption bandwidth of 6.7 GHz (10.6 ∼ 17.3 GHz) with a thickness of only 2.5 mm in the perpendicular direction to the aligned slit-like channels, while its RLmin was only −11 dB at 15.9 GHz in the orientation direction of slit-like channels. The composite aerogel had prominent thermal stability, with T5% in nitrogen up to 564 °C. The high temperature resistant and lightweight polyimide-based highly efficient EMW absorbing structural material manufactured by this research had great potential for aerospace applications.

Flexible sensors based on assembled carbon nanotubes

AbstractFlexible sensors have attracted significant attention as they could be directly attached to/implanted into the body or incorporated into textiles to monitor human activities and give feedbacks for healthcare. A typical fabrication method is the direct use of intrinsically flexible active materials such as carbon nanotubes (CNTs). CNTs are generally assembled into aligned structures to extend their remarkable chemical, mechanical, and electrical properties to macroscopic scale to afford high sensing performances. In this review, we present the recent advance of CNT assemblies as electrodes or functional materials for flexible sensors. The realizations of aligned CNTs are firstly investigated. A variety of flexible sensors based on the aligned CNTs are then carefully explored, with an emphasis on understanding the working mechanism for their high sensing properties. The main attention is later paid to comparing two main categories of flexible sensors with fiber and film shapes. The remaining challenges are finally highlighted to offer some insights for future study.

Constructing highly aligned crystalline structure to enhance sliding wear performance of bulk polyamide 6

High performance wear-resistant polyamide 6 (PA6) not only needs low friction and wear, but also requires high thermal conductivity and outstanding mechanical strength. Introducing lubricants into polymers has proved to be a feasible method, however, the contribution of intrinsic structure of PA6 to tribological properties is often ignored. Herein, a novel approach to fabricate high performance wear-resistant bulk PA6 via constructing a highly aligned crystalline structure was proposed. Firstly, an intense flow field applied by force assembly elements (FAEs) was introduced into extrusion processing to prepare PA6 precursor sheets with initially aligned molecular chains. Next, the precursor sheets were uniaxially drawn at 120 °C to achieve highly aligned crystalline structure at low draw ratio. The X-ray diffraction results showed the crystal orientation of the precursor sheets is 42% higher than that of samples prepared without FAEs. Furthermore, tensile stress induced γ-α phase transition and improved the crystallinity. As a result, the friction coefficient and wear rate of the bulk PA6 decreased 50.8% and 64.9%, respectively. Note that the maximum contact surface temperature reduced from 109.8 to 64.8 °C during high-speed friction because of the increasement of the thermal conductivity, effectively avoiding the aggravation of wear caused by surface softening. Moreover, the bulk PA6 also has excellent mechanical properties with a yield strength of 242 MPa and an elongation at break of 90%. Such remarkable enhancements in both mechanical and tribological properties are primarily attributed to the highly aligned crystalline structure with high α crystal form content. This work provides a way to design mechanically robust, wear-resistant polyamide applied in industry, transportation, etc.

Growth and NO2 gas sensing mechanisms of vertically aligned 2D SnS2 flakes by CVD: Experimental and DFT studies

Two dimensional chalcogenides and metal sulfide materials with their sensitive surfaces are promising and potential postulant for the purpose of chemical gas sensing as a consequence of extraordinary vast surface area to volume ratio and significant band gap. We demonstrate a highly selective and sensitive NO2 gas sensor using vertically aligned 2D SnS2 flakes, grown by a chemical vapor deposition method in controlled gas flow. The vertically aligned SnS2 flakes were confirmed by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. The sensing behaviour of the vertical aligned structures was analyzed for various concentrations of NO2 at different temperatures. The sensor exhibits high gas sensing response (ΔR/R%) of ~164 at 120 °C with 50 ppm of NO2 gas, which is the highest response among the SnS2 based reports. The device shows excellent sensing response at room temperature but poor recovery. The selectivity of the sensor was performed under different gas environments and found highly selective towards NO2 gas, and the results are supported by electronic structure calculations. Based on experimental results and electronic structure calculations, a gas sensing mechanism is proposed. The result indicates that fabricated sensor can be used in air purification industries and in air monitoring.

Flexible pillar-base structured piezocomposite with aligned porosity for piezoelectric energy harvesting

Flexible piezoelectric energy harvesters have attracted significant attention in recent years due to their ability to convert strain energy associated with bending into electrical energy for low-power wearable electronic devices. Compared with 0–3 type piezoelectric composites, where the piezoelectric phase is isolated within the material, flexible piezoelectric energy harvesters based on a three-dimensional interconnected ceramic skeleton are of particular interest due to their high stress transfer capability and high piezoelectric coefficients. Herein, a three-dimensional interconnected porous barium calcium zirconate titanate (BCZT) pillar-based structure is created via freeze casting, where polydimethylsiloxane (PDMS) is impregnated into the aligned pore channels to form a flexible piezoelectric energy harvester. The effect of porosity on piezoelectric coefficients, ferroelectric properties and energy harvesting performance is investigated in detail. The piezoelectric coefficient and energy harvesting figure of merit are significantly enhanced due to the presence of an aligned pore structure which leads to a high transfer of applied stress into the piezoelectric phase. The highly aligned porosity leads to the creation of a piezoelectric composite with 60 vol% of polymer that exhibits a high output voltage of 30.2 V and current of 13.8 μA. Moreover, the peak power density can reach up to 96.2 μW cm −2 , which is significantly higher than that of nanoparticle-based piezoelectric composites. This work demonstrates a promising prospect of utilizing flexible piezoelectric composites for energy harvesting applications. A flexible piezoelectric energy harvester based on BCZT pillar-base composite with aligned porosity is achieved via a freeze casting technique. Enhanced piezoelectric properties and energy harvesting performance ( V = 30.2 V, I = 13.8 μA at a porosity of 60 vol%) are realized due to the high poling efficiency and improved stress transfer, which is capable of charging capacitors and illuminating commercial LEDs. • Flexible pillar-base structured piezocomposite with highly aligned porosity is developed via freeze casting. • The piezoelectric energy harvesting performance is significantly enhanced due to the presence of an aligned pore structure. • Piezoelectric composite with 60 vol% of polymer exhibits a maximum power density of 96.2 μWcm −2 . • It is demonstrated to have the ability to charge capacitors and illuminate commercial LED bulbs.

Prevalence of strabismus among preschool children in eastern China and comparison at a 5-year interval: a population-based cross-sectional study

ObjectiveTo update data on strabismus and evaluate the changes in prevalence and patterns among preschoolers in eastern China over a period of 5 years.DesignNanjing Eye Study, a longitudinal population-based study.SettingRecruitment...

Transport In and Optimization of Aligned-Channel Li-Ion Electrode Architectures

Advanced electrode architectures utilizing aligned channels show promise in improving rate performance. However, the relationship between aligned channel structure and electrode-scale ion transport rate must be understood to enable optimization of electrode designs. Using a physics-based P2D model for experimental analysis, the impact of aligned channel electrode structures on cell rate capability is quantified. Results are used for optimization of aligned-channel volume fraction and electrode mass loading. Anticipated improvements in volumetric energy density over optimal for conventional, slurry-cast electrodes are shown to be significant at high rates and with electrodes characterized by high tortuosity.

Local H I filaments driven by a small-scale dynamo

Context. H I filaments are closely related to dusty magnetized structures that are observable in the far infrared (FIR). Recently it was proposed that the coherence of oriented H I structures in velocity traces the line of sight magnetic field tangling. Aims. We study the velocity-dependent coherence between FIR emission at 857 GHz and H I on angular scales of 18′. Methods. We use HI4PI H I data and Planck FIR data and apply the Hessian operator to extract filaments. For coherence, we require that local orientation angles θ in the FIR at 857 GHz along the filaments be correlated with the H I. Results. We find some correlation for H I column densities at |vLSR| < 50 km s−1, but a tight agreement between FIR and H I orientation angles θ exists only in narrow velocity intervals of 1 km s−1. Accordingly, we assign velocities to FIR filaments. Along the line of sight these H I structures show a high degree of the local alignment with θ, as well as in velocity space. Interpreting these aligned structures in analogy to the polarization of dust emission defines an H I polarization. We observe polarization fractions of up to 80%, with averages of 30%. Orientation angles θ along the filaments, projected perpendicular to the line of sight, are fluctuating systematically and allow a characteristic distribution of filament curvatures to be determined. Conclusions. Local H I and FIR filaments identified by the Hessian analysis are coherent structures with well-defined radial velocities. H I structures are also organized along the line of sight with a high degree of coherence. The observed bending of these structures in the plane of the sky is consistent with models for magnetic field curvatures induced by a Galactic small-scale turbulent dynamo.

Controlled Vertically Aligned Structures in Polymer Composites: Natural Inspiration, Structural Processing, and Functional Application.

Vertically aligned structures, which are a series of characteristic conformations with thickness-direction alignment, interconnection, or assembly of filler in polymeric composite materials that can provide remarkable structural performance and advanced anisotropic functions, have attracted considerable attention in recent years. The past two decades have witnessed extensive development with regard to universal fabrication methods, subtle control of morphological features, improvement of functional properties, and superior applications of vertically aligned structures in various fields. However, a systematic review remains to be attempted. The various configurations of vertical structures inspired from biological samples in nature, such as vertically aligned structures with honeycomb, reed, annual ring, radial, and lamellar configurations are summarized here. Additionally, relevant processing methods, which include the transformation of oriented direction, external-field inducement, template method, and 3D printing method, are discussed in detail. The diverse applications in mechanical, thermal, electric, dielectric, electromagnetic, water treatment, and energy fields are also highlighted by providing representative examples. Finally, future opportunities and prospects are listed to identify current issues and potential research directions. It is expected that perspectives on the vertically aligned structures presented here will contribute to the research on advanced multifunctional composites.

Synergic adhesive chemistry-based fabrication of BMP-2 immobilized silk fibroin hydrogel functionalized with hybrid nanomaterial to augment osteogenic differentiation of rBMSCs for bone defect repair

Bone defect repair and tissue engineering is specifically challenging process because of the distinctive morphological and structural behaviours of natural bone with complex healing and biochemical mechanisms. In the present investigation, we designed dopamine adhesive chemistry-based fabrication of silk fibroin hydrogel (SFD) with incorporation of nano-hydroxyapatite (nHA)-graphene oxide (GO) hybrid nanofillers with well-arranged porous morphology immobilized with bone morphogenic protein-2 (BMP-2) for the effective in vitro rabbit bone marrow derived mesenchymal stem cells loading compatibility and in vivo new bone regrowth and collagen deposition ability. We have achieved bone-specific hydrogel scaffolds with upgraded structural features, mechanical properties and particularly promoted in vitro osteogenic differentiation and compatibility of rabbit bone marrow mesenchymal stem cells (rBMSCs). Structural and microscopic analyses established greater distributions of components and well-ordered and aligned porous structure of the hydrogel network. In vivo result of new bone regrowth was promisingly higher in the Bm@nHG-SFD hydrogel (85%) group as compared to the other treatment groups of nHG-SFD (77%) and nH-SFD (64%) hydrogel. Overall, we summarized that morphologically improved hydrogel material with immobilization of BMP-2 could be have more attentions for new generation bone regeneration therapies.

The sorption and separation mechanism of CO2 in covalent organic frameworks with different aligned structures: DFT and molecular dynamic simulations

Insight into the sorption and separation mechanism of CO2 in covalent organic frameworks (COFs) is vital for efficient CO2 capture and separation. It is noted that COFs with amine functional groups facilitates CO2sorption compared with the other COFs. Firstly, COFs with hydrazone-based functional groups as an example is used to analyze the interactions of CO2 with hydrazone-based COFs (N-COFs) and the effect of stacking pattern (AA and AB staking) on CO2 sorption and separation property in different mixed gases by DFT and molecular dynamic simulation. Secondly, the CO2 separation effects of N-COFs with different layer spacing and pore size were compared. The results showed that the stronger interaction of CO2 with N-COFs result in higher sorption capacity of CO2 compared with that of the other gas, which facilitate the storage and separation of CO2. Moreover, the stacking pattern of N-COFs result in the different migration path ofgases, and the CO2 separation effect of N-COFs are improved by adjusting its layer spacing and pore size. In conclusion, the separation of N-COFs for CO2 is affected by the combined action of CO2 adsorption energy, the species of the mixed gas and the size sieving effect.

Microstructure Dependence of Output Performance in Flexible PVDF Piezoelectric Nanogenerators.

Flexible piezoelectric nanogenerators have attracted great attention due to their ability to convert ambient mechanical energy into electrical energy for low-power wearable electronic devices. Controlling the microstructure of the flexible piezoelectric materials is a potential strategy to enhance the electrical outputs of the piezoelectric nanogenerator. Three types of flexible polyvinylidene fluoride (PVDF) piezoelectric nanogenerator were fabricated based on well-aligned nanofibers, random oriented nanofibers and thick films. The electrical output performance of PVDF nanogenerators is systematically investigated by the influence of microstructures. The aligned nanofiber arrays exhibit highly consistent orientation, uniform diameter, and a smooth surface, which possesses the highest fraction of the polar crystalline β phase compared with the random-oriented nanofibers and thick films. The highly aligned structure and the large fraction of the polar β phase enhanced the output performance of the well-aligned nanofiber nanogenerator. The highest output voltage of 14 V and a short-circuit current of 1.22 µA were achieved under tapping mode of 10 N at 2.5 Hz, showing the potential application in flexible electronic devices. These new results shed some light on the design of the flexible piezoelectric polymer-based nanogenerators.