Hollow Microtubules Research Articles

Template-Free Self-Assembly of Hollow Microtubular Covalent Organic Frameworks for Oral Delivery of Insulin.

Covalent organic frameworks (COFs) have demonstrated versatile application potential since their discovery. Although the structure of COFs is orderly arranged, the synthesis of controllable macrostructures still faces challenges. Herein, we report, to our knowledge, the first template-free self-assembled COF-18 Å hollow microtubule (MT-COF-18 Å) structure and its use for insulin delivery that exhibits high loading capacity, gastroresistance, and glucose-responsive properties. The hollow MT-COF-18 Å was achieved by a template-free method benefiting from the mixed solvents of mesitylene and dioxane. The formation mechanism and morphology changes with insulin loading and release were observed. In Caco-2 cells, the transferrin-coated system demonstrated enhanced insulin cellular uptake and transcellular transport, which indicated great potential for oral applications. Additionally, the composites presented sustained glycemic control and effective insulin blood concentrations without noticeable toxicity in diabetic rats. This work shows that hollow microtubular COFs hold great promise in loading and delivery of biomolecules.

Catkin-derived carbon microtubes for hybrid anode materials of high-performance lithium ion batteries

As a common biological waste, catkin shows negligible economic value and is hazardous to the environment and human respiratory health. To turn waste into treasure, in this work, a hybrid anode is successfully prepared by using the catkin-derived 1D hollow carbon microtube as dispersing agents to well disperse the MnO particles via a simple one-step pyrolysis method. Benefiting from the high electrical conductivity and hollow microtubule structure of the catkin-derived carbon, as well as the evenly dispersion of the MnO particles and the interfacial energy storage of Mn0/Li2O interfaces, the lithium ion battery based on the resultant MnO/C hybrid anode exhibits outstanding rate performance (high reversible specific capacity of 1365 mAh g−1 at a current density of 0.1 A g−1 and maintains 451 mAh g−1 even at a high current density of 6.4 A g−1) and superior cycling stability (retains ∼100 % after 1000 cycles at a current density of 0.8 A g−1). This work conforms to the development concept of green environmental protection and realizes the unity of economic and social benefits.

Electrooxidation Performance of a Cotton-Cloth-Derived, Ni-Based, Hollow Microtubular Weave Catalytic Electrode for Methanol and Urea

Increasing consumption produces a large amount of cotton textile waste, the conversion of which into porous metals used for energy purposes is of practical value. In this paper, a porous, Ni-based, hollow microtubular weave (Ni-HTW) is obtained from cotton weave by high-temperature carbonization and hydrothermal synthesis with high-temperature reduction. The Ni-based, hollow microtubules in this weave have a diameter of 5–10 μm and a wall thickness of about 1 μm, and every 15 microtubules form a loose bundle with a diameter of 150–200 μm. For improved performance, Ni(OH)2 nanosheets are further electrodeposited on the fibers’ surface of the Ni-HTW to form a nano-Ni(OH)2/Ni-HTW composite electrode with a core–shell heterostructure where Ni is the core and Ni(OH)2 the shell. The combination of hollow microtubule weave morphology and nanosheet structure results in a large specific surface area and abundant active sites, and the composite electrode shows excellent electrocatalytic performance and long-term stability for methanol oxidation (MOR) and urea oxidation (UOR). The current densities can reach 303.1 mA/cm2 and 342.5 mA/cm2 at 0.8 V, and 92.29% (MOR) and 84.41% (UOR) of the pre-cycle current densities can be maintained after 2000 consecutive cycles.

An electrochemical immunosensor based on polyaniline microtubules and zinc gallinate for detection of human growth differentiation factor-15.

The incidence rate of cardiovascular diseases (CVDs) remains high, and their mortality rate is significantly higher than that of other diseases. Growth differentiation factor-15 (GDF-15) is a recently developed biomarker for the early diagnosis and prognostic evaluation of CVDs because its concentration in serum increases substantially after a cardiovascular injury or an inflammatory reaction. In this study, a sandwich-type immunosensor was constructed for the sensitive detection of GDF-15. Specifically, peony-like zinc gallinate (ZnGa2O4) prepared using a hydrothermal method, which exhibits excellent electrocatalytic performance, was coupled with Au nanoparticles (NPs) to obtain golden-peony-like ZnGa2O4/Au NPs. Theypreserved the immune activity of GDF-15 antibody molecules and further enhanced the conductivity, thereby realizing additional signal amplification. Hollow polyaniline (PANI) microtubules decorated with Pd NPs were used as the sensing platform (PANI/Pd NPs). The hollow microtubules provided abundant active sites and considerably improved the electron-transfer rate. Under optimal conditions, a linear range and remarkably low detection limit of 100fgmL-1-10ngmL-1 and 42.23fgmL-1, respectively, were achieved. These experimental results indicate that the strategy reported herein can be adopted as a novel approach for the convenient and rapid detection of GDF-15.

Efficient photocatalytic reduction of CO2 by improving adsorption activation and carrier utilization rate through N-vacancy g-C3N4 hollow microtubule

The g-C3N4 is considered to be a promising non-metallic semiconductor photocatalyst for converting CO2 into value-added products. However, g-C3N4 undergoes recombination of photogenerated electrons and holes and its low CO2 adsorption capacity. Here, g-C3N4 hollow microtube (TCN) structure with tunable N-vacancy concentrations (TCN-1) was controllably fabricated by hydrothermal self-assembly followed by H2 heat treatment. The resultant N-vacancy with one-dimensional structure g-C3N4 exhibits excellent activity for photocatalytic CO2 reduction, giving the CO generation rate of 7.06 μmol/g/h (TCN-1) under visible-light illumination without any co-catalyst or a sacrificial agent, which is 2.2- and 8.8- times that of TCN (3.12 μmol/g/h) and pristine g-C3N4 (0.75 μmol/g/h). It is well evidenced with experiments and DFT calculations that N-vacancy mainly originates from the selective cleavage of C=N–C sites on the surface of g-C3N4. The N-vacancy can act as electron trap, extending the lifetime of charge carriers. Moreover, the changes in the electron distribution around the vacancies thereby provide the driving force for the dissociation of excitons, which in turn promotes the activation of CO2 adsorption. The bifunctional of g-C3N4 with structural optimization and defect design is a very promising candidate for enhancing the adsorption-activation of reactants and the carrier utilization of photocatalysts in the photocatalytic process.

Characterization and In Vitro Fecal Microbiota Regulatory Activity of a Low-Molecular-Weight Exopolysaccharide Produced by Lactiplantibacillus plantarum NMGL2.

The exopolysaccharide (EPS) produced by Lactiplantibacillus plantarum NMGL2 isolated from traditional fermented dairy cheese was purified chromatographically with DEAE-Sepharose and Sepharose CL-6B columns. The purified EPS was characterized by various physicochemical methods and in vitro fecal microbiota regulation assay. The results showed that the EPS had a relatively low molecular weight of 3.03 × 104 Da, and it had a relatively high degradation temperature of 245 °C as determined by differential scanning calorimetry. Observation of the EPS by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy revealed a highly branched and tangled fibrous network microstructure with many hollow microtubules and spherical particles. Structural study by 1H NMR spectroscopy suggested that the EPS contained a tetrasaccharide repeating unit with monosaccharide components of β-galactose (4.6%), α-glucose (20.6%), and α-mannose (74.8%). The EPS was highly resistant to hydrolysis of simulated human saliva, gastric, and intestinal juices. Moreover, the EPS beneficially affected the composition and diversity of the fecal microbiota, e.g., increasing the relative abundance of Firmicutes and inhibiting that of Proteobacteria. The results of this study indicated significant bioactivity of this novel low-molecular-weight EPS produced by Lpb. plantarum NMGL2, which could serve as a bioactive agent for potential applications in the food and health care industry.

Absorbent cotton derived mesoporous CeO2 hollow tubule for enhanced detection of p-xylene at low energy consumption

Ultra-sensitive detection of flammable and carcinogenic p-xylene gas at relatively low energy consumption through metal oxide-based sensors remains a great challenge due to its high stability. Herein, mesoporous CeO2 hollow microtubules with cubic fluorite structure were simply prepared by immersing absorbent cotton into cerium salt and subsequent calcination. The effect of calcination temperature on the microstructure and gas-sensing performance was also studied. The CeO2-500 hierarchical structure calcinated at 500 °C is composed of cross-linked nanoparticles with small size (12 nm), which possesses relatively large specific surface area (60.8 m2·g−1), well-distributed mesopores (15.0 nm) and abundant oxygen vacancy defects. At a relatively low operating temperature of 133 °C, CeO2-500 sensor shows a fast response to 100 ppm p-xylene (Tres = 5.4 s) and detection limit of 100 ppb, which represents the lowest value in reported CeO2-based sensors. Such excellent gas-sensing performance is highly related to the intrinsic structural properties of mesoporous CeO2-500 hollow microtubule, surface adsorbed oxygen and oxygen vacancy defects caused by Ce3+ ions.

Microtubules form by progressively faster tubulin accretion, not by nucleation-elongation.

Microtubules are dynamic polymers that play fundamental roles in all eukaryotes. Despite their importance, how new microtubules form is poorly understood. Textbooks have focused on variations of a nucleation-elongation mechanism in which monomers rapidly equilibrate with an unstable oligomer (nucleus) that limits the rate of polymer formation; once formed, the polymer then elongates efficiently from this nucleus by monomer addition. Such models faithfully describe actin assembly, but they fail to account for how more complex polymers like hollow microtubules assemble. Here, we articulate a new model for microtubule formation that has three key features: (1) microtubules initiate via rectangular, sheet-like structures that grow faster the larger they become; (2) the dominant pathway proceeds via accretion, the stepwise addition of longitudinal or lateral layers; and (3) a "straightening penalty" to account for the energetic cost of tubulin's curved-to-straight conformational transition. This model can quantitatively fit experimental assembly data, providing new insights into biochemical determinants and assembly pathways for microtubule nucleation.

Formation of NiCo2O4 hierarchical tubular nanostructures for enhanced xylene sensing properties

Complex hollow structures with ultra-thin 2D building blocks represent a unique type of functional nanostructures because of their structural merits. In this work, hierarchical NiCo2O4 hollow microtubules assembled by ultra-thin 2D nanosheets have been successfully prepared via a template-assisted process with subsequent etching treatment. The purity, morphology, crystallographic information and surface chemical composition of as-obtained hierarchical NiCo2O4 hollow microtubules are characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM),transmission electron microscopy (TEM), element mapping, X-ray photoelectron spectroscopy (XPS) and Nitrogen adsorption–desorption analysis. Gas sensing performance of hierarchical NiCo2O4 hollow microtubules is discussed in detail. The results show that hierarchical NiCo2O4 hollow microtubules not only exhibit rapid response/recovery (20/9 s) speed to 100 ppm xylene at relatively low working temperature of 220 °C, but also show low detection limit (1 ppm), high response, excellent gas selectivity and superior long-term stability, which are significantly better than irregular NiCo2O4 nanosheets. The results demonstrate that unique hierarchical NiCo2O4 hollow microtubules are promising candidates for efficient and reliable detection of xylene.

The inner junction complex of the cilia is an interaction hub that involves tubulin post-translational modifications.

Microtubules are cytoskeletal structures involved in stability, transport and organization in the cell. The building blocks, the α- and β-tubulin heterodimers, form protofilaments that associate laterally into the hollow microtubule. Microtubule also exists as highly stable doublet microtubules in the cilia where stability is needed for ciliary beating and function. The doublet microtubule maintains its stability through interactions at its inner and outer junctions where its A- and B-tubules meet. Here, using cryo-electron microscopy, bioinformatics and mass spectrometry of the doublets of Chlamydomonas reinhardtii and Tetrahymena thermophila, we identified two new inner junction proteins, FAP276 and FAP106, and an inner junction-associated protein, FAP126, thus presenting the complete answer to the inner junction identity and localization. Our structural study of the doublets shows that the inner junction serves as an interaction hub that involves tubulin post-translational modifications. These interactions contribute to the stability of the doublet and hence, normal ciliary motility.

Preparation and electrochemical performance of flower-like ZnMn2O4 hollow microtubules

The flower-like ZnMn2O4 hollow microtubules were synthesized by a hydrothermal method and calcination method. The composition and morphology were characterized. The results showed that flower-like hollow microtubules were obtained through calcination treatment. The as-prepared ZnMn2O4 electrochemical properties of flower-like hollow microtubules anode material for lithium-ion batteries were investigated. The first charge and discharge capacity was measured at 2152/1263 mA h g−1 when the current density at 400 mA g−1. After 300 cycles, the capacity kept 515 mA h g−1 corresponding to the coulombic efficiency of 99%, which exhibited preferable cycling performance. The stability of the structure has been shown by rate performance, which had been tested under different current density. The results suggest a promising application of the ZnMn2O4 as anode material for lithium-ion batteries.

TAPping into the treasures of tubulin using novel protein production methods.

Microtubules are cytoskeletal elements with important cellular functions, whose dynamic behaviour and properties are in part regulated by microtubule-associated proteins (MAPs). The building block of microtubules is tubulin, a heterodimer of α- and β-tubulin subunits. Longitudinal interactions between tubulin dimers facilitate a head-to-tail arrangement of dimers into protofilaments, while lateral interactions allow the formation of a hollow microtubule tube that mostly contains 13 protofilaments. Highly homologous α- and β-tubulin isotypes exist, which are encoded by multi-gene families. In vitro studies on microtubules and MAPs have largely relied on brain-derived tubulin preparations. However, these consist of an unknown mix of tubulin isotypes with undefined post-translational modifications. This has blocked studies on the functions of tubulin isotypes and the effects of tubulin mutations found in human neurological disorders. Fortunately, various methodologies to produce recombinant mammalian tubulins have become available in the last years, allowing researchers to overcome this barrier. In addition, affinity-based purification of tagged tubulins and identification of tubulin-associated proteins (TAPs) by mass spectrometry has revealed the ‘tubulome’ of mammalian cells. Future experiments with recombinant tubulins should allow a detailed description of how tubulin isotype influences basic microtubule behaviour, and how MAPs and TAPs impinge on tubulin isotypes and microtubule-based processes in different cell types.

Emerging Picture of Deuterosome-Dependent Centriole Amplification in MCCs.

Multiciliated cells (MCCs) have several hair-like structures called cilia, which are required to propel substances on their surface. A cilium is organized from a basal body which resembles a hollow microtubule structure called a centriole. In terminally differentiated MCCs, hundreds of new basal bodies/centrioles are formed via two parallel pathways: the centriole- and deuterosome-dependent pathways. The deuterosome-dependent pathway is also referred to as “de novo” because unlike the centriole-dependent pathway which requires pre-existing centrioles, in the de novo pathway multiple new centrioles are organized around non-microtubule structures called deuterosomes. In the last five years, some deuterosome-specific markers have been identified and concurrent advancements in the super-resolution techniques have significantly contributed to gaining insights about the major stages of centriole amplification during ciliogenesis. Altogether, a new picture is emerging which also challenges the previous notion that deuterosome pathway is de novo. This review is primarily focused on studies that have contributed towards the better understanding of deuterosome-dependent centriole amplification and presents a developing model about the major stages identified during this process.

Hollow Ni-Co layered double hydroxides-derived NiCo-alloy@g-C3N4 microtubule with high-performance microwave absorption

Hollow microtubule structured nano-/micromaterials of hollow tubular g-C3N4 (TCN) enwrapped with nanosheets were fabricated by a three-step method. By calcining NiCo-layered-double-hydroxides/tubular-cyanuric acid-melamine (NiCo-LDH/TCM) precursor prepared through using 2-methylimidazole as precipitant and methanol as solvent, the as-prepared NiCo-alloy@tubular-g-C3N4 (NC@TCN) shown excellent microwave absorption in the frequency range of 2–18 GHz. The optimal reflection loss (RL) of −35.63 dB was observed at 5.00 GHz and an effective absorption bandwidth of 4.80 GHz at a matching layer thickness of 2.0 mm. Our results indicated that the deposition of NiCo-alloy nanoparticles on g-C3N4 microtubule was an efficient way to fabricate g-C3N4-based high-performance microwave absorbers.

Ultrahigh sensitivity and selectivity chlorine gas sensing of In2O3 hollow microtubules by bio-template method with degreasing cotton

A simple two-stage procedure of immersion-calcination method has been developed for preparing In2O3 hollow microtubules by using degreasing cotton as soft bio-templates. The morphological feature was characterized as hollow microtubules with the range of 50–70 μm in length, 5–6 μm in width, and about 1 μm in thickness. The Cl2 sensing properties were remarkably enhanced in sensitivity and selectivity for In2O3 hollow microtubules. The gas response (Rgas/Rair) of the In2O3 hollow microtubules sensor was 1051 to 10 ppm Cl2 at 200 °C, which was 25 times higher than In2O3 particles. Such outstanding gas sensing performance was ascribed to the hollow morphology, which revealed high specific surface area, abundant oxygen vacancies and low band gap. The gas sensing mechanism was deduced that Cl2 molecules are directly adsorbed on the metal oxide surface and oxygen vacancies.

Flexible P-Doped Carbon Cloth: Vacuum-Sealed Preparation and Enhanced Na-Storage Properties as Binder-Free Anode for Sodium Ion Batteries.

In this work, a flexible and self-supporting P-doped carbon cloth (FPCC), which is composed of interwoven mesh of hollow microtubules with porous carbon walls, is prepared via a vacuum-sealed doping technology by employing the commercially available cotton cloth as sustainable and scalable raw material. When directly used as binder-free anode for sodium-ion batteries, the as-prepared FPCC delivers superior Na-storage properties in terms of specific capacity up to 242.4 mA h g-1, high initial Coulombic efficiency of ∼72%, excellent rate capabilities (e.g., 123.1 mA h g-1 at a high current of 1 A g-1), and long-term cycle life (e.g., ∼88% capacity retention after even 600 cycles). All these electrochemical data are better than the undoped carbon cloth control, demonstrating the significance of P-doping to enhance the Na-storage properties of cotton-derived carbon anode. Furthermore, the technologies of electrochemical impedance spectroscopy and galvanostatic intermittent titration technique are implemented to disclose the decrease of charge transfer resistance and improvement of Na-migration kinetics, respectively.

Post-synthetic regulation of the structure, morphology and photoactivity of graphitic carbon nitride by heat-vacuum treatment

This work provides a simple but efficient strategy for the adjustment of texture and regular morphology of graphitic carbon nitride (CN) material by the post-synthesis of successive heat-vacuum treatment (SHVT) method without using hard templates. The modified CN displayed various hollow microtubule structure and the improvement of s-heptazine unit depending on the SHVT temperature. The best hollow microtubule morphology with highest contents of the key s-heptazine structure can be achieved by SHVT at 540°C. These modified CN samples led to the highest photocatalytic H2 yield of 1160μL for 4h reaction under visible light irradiation, which is almost 10 times higher than that of the traditional CN (118μL). The results represent an alternative approach to preparing hollow microtubule morphology and improving the s-heptazine structure in CN for enhancing photocatalytic performance.

Fabrication of hollow In2O3–ZnO microtubules by a simple biotemplate method and their gas-sensing properties

Biomorphic In2O3–ZnO hollow microtubules were synthesized by using cotton as template and followed by calcination. This environmental-friendly method using biomaterials as templates can be used to synthesize metal oxide semiconductor materials with specific morphologies. The structural and microscopy characterization were carried out with X-ray diffraction, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy. The SEM images display the porous structure of the as-obtained hollow microtubules, which is beneficial to increase gas sensing properties of materials. Gas sensors based on In2O3-doped ZnO hollow microtubules were investigated and the test results demonstrate the excellent acetone sensing properties of such porous materials. The response of In2O3–ZnO hollow microtubule sensors to 100 ppm acetone at the optimum temperature of 300 °C is 62.5, meanwhile the response and recovery times are 3 and 7 s, respectively. Moreover, even at 0.1 ppm of acetone detectable response can be observed, and the value is 2.82. At the same time the sensors have selectivity to acetone.

A Tunable Scaffold of Microtubular Graphite for 3D Cell Growth.

Aerographite (AG) is a novel carbon-based material that exists as a self-supportive 3D network of interconnected hollow microtubules. It can be synthesized in a variety of architectures tailored by the growth conditions. This flexibility in creating structures presents interesting bioengineering possibilities such as the generation of an artificial extracellular matrix. Here we have explored the feasibility and potential of AG as a scaffold for 3D cell growth employing cyclic RGD (cRGD) peptides coupled to poly(ethylene glycol) (PEG) conjugated phospholipids for surface functionalization to promote specific adhesion of fibroblast cells. Successful growth and invasion of the bulk material was followed over a period of 4 days.

The role of dynamic instability in microtubule organization.

Microtubules are one of the three major cytoskeletal components in eukaryotic cells. Heterodimers composed of GTP-bound α- and β-tubulin molecules polymerize to form microtubule protofilaments, which associate laterally to form a hollow microtubule. Tubulin has GTPase activity and the GTP molecules associated with β-tubulin molecules are hydrolyzed shortly after being incorporated into the polymerizing microtubules. GTP hydrolysis alters the conformation of the tubulin molecules and drives the dynamic behavior of microtubules. Periods of rapid microtubule polymerization alternate with periods of shrinkage in a process known as dynamic instability. In plants, dynamic instability plays a key role in determining the organization of microtubules into arrays, and these arrays vary throughout the cell cycle. In this review, we describe the mechanisms that regulate microtubule dynamics and underlie dynamic instability, and discuss how dynamic instability may shape microtubule organization in plant cells.