Porous Microtubes Research Articles

Electrokinetic energy conversion of nanofluids in porous microtubes with Green’s function

Abstract Micro-devices fabrication has led to extensive scientific research on microfluidics and microelectromechanical systems. These devices are used for a wide range of technological applications, but research on microfluidic devices for nanofluids is relatively scarce. In response to this problem, the electrokinetic energy conversion (EKEC) efficiency of nanofluids is provided under the coupling effect of pressure gradient and magnetic field through porous microtubes using the Debye–Hückel linearization and the Green’s function method. The results show that the periodic excitation of the square waveform is more effective in increasing the EKEC efficiency. In addition, compared with previous studies, the average velocity is in good agreement with the cosine waveform at R = 0.2. It is worth noting that compared to cosine waves, the average velocity reaches 47% in triangular waves and 85% in square waves.

Rapid Construction of 3D Biomimetic Capillary Networks with Complex Morphology Using Dynamic Holographic Processing

AbstractMicrovascular networks (MVNs) are crucial transportation systems in living creatures for nutrient distribution, fluid flow, energy transportation and so on. However, artificial manufacturing of MVNs, especially capillary networks with diameters (average 6 ≈ 9 µm), has always been a problem and bottleneck in tissue engineering due to the lack of efficient manufacturing methods. Herein, a dynamic holographic processing method is reported for producing 3D capillary networks with complex biomimetic morphologies. Combining the axial scanning of the focused beam and the dynamic display of holograms, biomimetic bifurcated microtubes, and porous microtubes with programmable morphologies are rapidly produced by two‐photon polymerization (TPP). As a proof‐of‐concept demonstration, porous microtubes are used as 3D capillary network scaffolds for culturing human umbilical vein endothelial cells (HUVECs) to facilitate the exchange of nutrients and metabolites. Endothelial cells around the vascular scaffolds manifest obvious tight connections and 3D coverage after 3 days in vitro, which reveals that the scaffolds play a significant role in the morphology of dense vascularization. This flexible and rapid method of producing capillary networks provides a versatile platform for vascular physiology, tissue regeneration, and other biomedical areas.

Biomimetic hydrogel scaffolds embedded with porous microtubes as perfusion channels

Despite the remarkable progress in biofabrication, the vascularization of large-sized tissue scaffolds remains a great challenge for tissue engineering. The lack of effective capillary vessels in the scaffold can result in cellular necrosis due to the lack of oxygen and nutrients. Integrating capillary vessels in scaffolds is critical to maintaining cellular metabolic functions and the ultimate success of engineering large-scale tissues and organs. This paper demonstrates a novel hybrid biofabrication method that combines coaxial electrospinning and extrusion-based bioprinting to fabricate microtube-embedded hydrogel scaffolds. The porous microtubes mimicked the capillary morphology and were embedded between layers of 3D printed sodium alginate scaffold to function as a microchannel diffusion system. The dye diffusion test showed that the microtubes enhanced the mass transport within the scaffold.

Process control of electrospinning artificial fenestrated capillary vessels

Rapid fabrication of capillary vessels is important for tissue engineering because local perfusion and oxygen exchange within the tissue depend on the network of capillaries which have diameters ranging from 5 to 10 µm. Fenestrated capillaries are microvessels that have surface pores of 80 to 100 nm in diameter. These capillaries are essential for many organs, such as small intestines, endocrine glands, and kidneys. In this paper, we presented a wet coaxial electrospinning technique for the rapid fabrication of porous microtubes as artificial fenestrated capillaries using polycaprolactone and polyethylene oxide. We characterized the effects of process parameters on the morphological features of these microtubes by regression modeling. Our study shows that the flow rate ratio of the core/sheath solutions and the viscosity of the sheath solution play a significant role in the outside diameter, wall thickness, and hollow area of the microtubes. In addition, the formation of surface pores is dominated by the humidity during the electrospinning. At the same humidity level, the size of the surface pores is positively correlated with the viscosity of the sheath solution and the outside diameter of the microtubes. Overall, this study established the process-property relationship for wet coaxial electrospinning of artificial fenestrated capillaries.

Degradable Biocompatible Porous Microtube Scaffold for Extended Donor Cell Survival and Activity.

Cell therapy has significant therapeutic potential but is often limited by poor donor cell retention and viability at the host implantation site. Biomaterials can improve cell retention by providing cells with increased cell-cell and cell-matrix contacts and materials that allow three-dimensional cell culture to better recapitulate native cell morphology and function. In this study, we engineered a scaffold that allows for cell encapsulation and sustained three-dimensional cell culture. Since cell therapy is largely driven by paracrine secretions, the material was fabricated by electrospinning to have a large internal surface area, micrometer-thin walls, and nanoscale surface pores to allow for nutrient exchange without early cell permeation. The material is degradable, which allows for less invasive removal of the implant. Here, a biodegradable poly(lactic-co-glycolic acid) (PLGA) microtube array membrane was fabricated. In vitro testing showed that the material supported the culture of human dermal fibroblasts for at least 21 days, with paracrine secretion of pro-angiogenic FGF2. In vivo xenotransplantation of human cells in an immunocompetent mouse showed that donor cells could be maintained for more than one month and the material showed no obvious toxicity. Analysis of gene expression and tissue histology surrounding the implant showed that the material produced muted inflammatory and immune responses compared to a permanent implant and increased markers of angiogenesis.

Visible-light-driven photoreforming of poly(ethylene terephthalate) plastics via carbon nitride porous microtubes.

It is highly desirable but challenging to realize efficient photoreforming of plastic waste over metal-free semiconductors. Here, we synthesized metal-free carbon nitride porous microtube (CNxPM) photocatalysts by carrying out a pyrolysis of the supramolecular assembly formed by the self-assembly of L-arginine (L-Arg) and melamine, the modification of L-Arg rationally engineering the microstructure and electronic structure of the CNxPM system for efficient visible-light-driven photoreforming of poly(ethylene terephthalate) (PET) to hydrogen (H2) and high-value chemicals. In particular, the amount of formate converted from PET substrate under visible light was highest in metal-free semiconductors without any co-catalyst reported so far, presenting the first example of visible-light-driven photoreforming of PET over a completely metal-free single-component semiconductor without any co-catalyst.

Efficient procedure for biodiesel synthesis from waste oil and t-butylation of resorcinol using a porous microtube polymer-based solid acid

A novel porous microtube polymer-based solid acid was synthesized via the polymerisation of naphthalene and sulfonation.

Accelerating Neurite Growth and Directing Neuronal Connections Constrained by 3D Porous Microtubes.

Investigation of neural growth and connection is crucial in the field of neural tissue engineering. Here, using a femtosecond laser direct writing (fs-DLW) technique, we propose a directionally aligned porous microtube array as a culture system for accelerating the growth of neurons and directing the connection of neurites. These microtubes exhibited an unprecedented guidance effect toward the outgrowth of primary embryonic rat hippocampal neurons, with a wrap resembling the myelin sheaths of neurons. The speed of neurite growth inside these microtubes was significantly faster than that outside these microtubes. We also achieved selective/directing connection of neural networks inside the magnetic microtubes via precise microtube delivery to a gap between two neural clusters. This work not only proposes a powerful microtube platform for accelerated growth of neurons but also offers a new idea for constructing biological neural circuits by arranging the size, location, and pattern of microtubes.

Rational Design of 1D Porous Carbon Microtubes Supporting Multi‐size Bi2O3 Nanoparticles for Ultra‐long Cycle Life Lithium‐Ion Battery Anodes

AbstractMulti‐size Bi2O3 nanoparticles supported by 1‐dimensional (1D) porous carbon microtubes (ms‐Bi2O3/CMTs) were favorably constructed through surface‐ion release and in‐ situ oxidation strategy. The prominent 1D porous microtube materials with multi‐size nanoparticles structure can furnish more plentiful electrochemical active sites and shorten lithium storage paths for high‐speed redox reactions, which was conducive to ion transport kinetics. The CV tests with various scan rates verified lithium storage mechanism of ms‐Bi2O3/CMTs with diffusion/capacitance control coexistence. The complexes illustrated an ultra‐long cycle life and extraordinary reversible capacity: it still had a specific capacity of 392.6 mAh g−1 after 3000 cycles at 1 A g−1; and it manifested 546.3 mAh g−1 when it returned to 0.05 A g−1 and continued to 100 cycles after experiencing different current densities of 0.05–5 A g−1, which indicated that ms‐Bi2O3/CMTs is a prospective anode for lithium‐ion batteries (LIBs).

Sulfur/phosphorus doping-mediated morphology transformation of carbon nitride from rods to porous microtubes with superior photocatalytic activity

Hetero-atoms doping or morphology controlling of carbon nitride (g-C3N4) can availably regulate its electronic band structure and optimize photocatalytic performance under visible light. Herein, sulful (S), phosphorus (P) co-doped porous carbon nitride microtubes (SPCN) was synthesized by using ammonium dihydrogen phosphate and melamine as precursors, in which ammonium dihydrogen phosphate can not only control the morphology of carbon nitride from nanorods to porous microtubes, but also provide a potential P source for P-doped CN. The prepared SPCN0.1 with the content of 0.1 g ammonium dihydrogen phosphate displayed the highest photocatalytic hydrogen generation rate of 4200.3 µmol g-1h−1, which was approximately 25 and 1.6 folds by bulk g-C3N4 (CN) and sulphur doped g-C3N4 microrods (SCN), respectively. Moreover, the apparent quantum efficiency of HER reached up to 10.3 % at 420 nm. The enhanced photocatalytic performance may be attributed to the synergistic effect of S, P doping and morphology structure of carbon nitride, which effectively accelerated the separation and transfer of photogenerated electron-hole pairs, proved by photoluminescence spectra, time-resolved PL spectra, electrochemical impedance spectrum and transient photocurrent responses. The novel synthetic method described in this paper is an effective approach to regulate the morphology of g-C3N4via non-metal doping with superior photocatalytic performance.

Effects of Solution Viscosity on Poly(l-Lactic Acid) Porous Microtubes Fabricated by Core–Sheath Electrospinning

Abstract Core–sheath electrospinning is a rapid microfabrication process for creating multilayer polymer microfibers. This paper presents a process based on core–sheath electrospinning to fabricate poly(L-lactic acid) (PLLA) microtubes with nanopores on the tube wall. The morphology of the microtubes mimics human fenestrated capillary vessels. This study investigates the effects of the viscosities of the core and the sheath solutions on the microtube outer diameter and the nanopore size. The core solution shows a dominating influence on the microtube diameter. At the same core solution viscosity level, the microtube diameter is negatively correlated to the core-to-sheath viscosity ratio. The pore size is positively correlated to the microtube diameter. Understanding the effects of solution viscosity on microtube morphology is the prerequisite for process control and microtube product development for future biomedical applications.

Thermally induced nonlinear stability and imperfection sensitivity of temperature- and size-dependent FG porous micro-tubes

An attempt is made in the current research to analyse the nonlinear thermal stability and imperfection sensitivity of functionally graded (FG) porous micro-tubes. Temperature-dependent properties of the geometrically imperfect micro-tube are graded across the radius of cross-section. It is assumed that the micro-tube with different end conditions is in contact with a two-parameter elastic foundation. The nonlinear component of the elastic foundation can be of the hardening or softening type. The equilibrium equations are obtained within the framework of von Karman nonlinear assumptions and high-order shear deformation tube theory. The governing equations are reformulated for the case of imperfect micro-tubes based on the modified couple stress theory. The system of nonlinear differential equations is solved using the two-step perturbation technique and Galerkin procedure. The analytical solutions are obtained for three different types of immovable boundary conditions which are clamped-rolling, simply-supported and clamped–clamped. The closed-form expressions are given to obtain the large deflection in the micro-tube as a function of the elevated temperature. Novel parametric studies are given to explore the thermal stability and imperfection sensitivity analysis of the perfect and imperfect micro-tubes, respectively. The effects of boundary conditions, couple stress components, porosity coefficient, elastic foundation, FG pattern, temperature dependence and geometrical parameters are studied.

Study of Heat Characteristics of Electroosmotic Mediator and Peristaltic Mechanism via Porous Microtube

Heat characteristics of electroosmotic peristaltic flow are investigated in the porous microtube. Flow and heat equations are modeled using the Jeffrey fluid and viscous dissipation, respectively. The wall is patterned with a periodic array of sinusoidal peristaltic waves. In the presence of axial electric field, the chemical interaction of electrolyte (Jeffrey fluid) and the peristaltic walls (solid) cause an electric double layer at the interface. Based on low Reynolds assumption and Debye-Huckel linearization, the Poisson-Boltzmann equation formally solves the potential distribution, and the resulting non-linear problem is numerically solved via the NDSolve built-in scheme of the computing software Mathematica. Expression of interest like electric potential, velocity, pressure gradient, temperature, streamlines, and wall shear stress are executed numerically within the Jeffrey fluid flow pattern. A complete parametric study is executed to find out the outturn of material parameter λ1, permeability of porous medium K, electroosmotic parameter me, mobility of the medium β, and Brinkman number Br on the thermal features of the flow. This model is also suitable for a wide range of biological microfluidic applications. It is observed that the morphology of heat transfer in the flow is found to be subject to the joint consequence of the geometry of the tube and wall properties. The axial velocity increases monotonically for the Jeffrey fluid when equated to the viscous fluid. Moreover, velocity is noticed to upsurge with higher values of electroosmotic parameter and declines for porous medium and mobility of medium. The magnitude of bolus is larger for the case of Newtonian fluid as compared with non-Newtonian Jeffery fluid. Porosity decays the temperature throughout the microtube. The results presented may potentially be applied to clinical cases associated with the intrapleural membranes, gastrointestinal tract, and capillaries.

Thermo-fluidic transport of electromagnetohydrodynamic flow of sodium alginate based Casson nano fluid passing through a porous microtube under the effect of streaming potential

Thermal transport characteristics of Casson nanofluid through a porous microtube is analyzed under the effect of streaming potential and constant pressure gradient with electrokinetic effect associated with applied magnetic field. An analytical solution of the velocity and temperature distribution of Casson-nano fluid through the porous microtube related to combining effects of electromagnetohydrodynamics forces under the effect of streaming potential have been obtained. The significant influences of various non-dimensional parameters on velocity and temperature profiles are discussed in this study. Also, it is revealed the impact of nano particles on flow transport and heat transfer phenomenon. Furthermore, the Nusselt number is calculated analytically. The variations of pertinent parameters such as Hartmann number, Darcy number,Casson parameter, volume friction parameter of nanoparticles, joule heating parameter are delineated graphically and discussed in details.

Thermal performance for electromagnetohydrodynamic flow of non-Newtonian Casson fluid through porous microtube

A theoretical investigation is done to analyze the heat transfer features of non-Newtonian Casson fluid in a porous microtube with electro kinetic effects associated with the applied magnetic field. The exact analytical solutions the velocity and temperature profiles of non-Newtonian Casson fluid in porous micro-tube related to combining effects of electromagnetohydrodynamics forces and electrokinetic forces have been obtained using a variation of parameter. Temperature and flow distribution characteristics of Casson fluid flow are controlled by the obtruded pressure-gradients, applied a magnetic field and electro-kinetic forces. The exciting features of the electromagnetohydrodynamics flow along with the features of the heat flow rate are examined by variation in the non-dimensional physical arguments on velocity and temperature functions. The effect of the Casson parameter on the velocity and temperature profiles has been investigated analyzed. The fluid flow rate and the heat transfer rate of Casson fluid within porous micro-tube is controlled by the strength applied electric and magnetic field.

Limit load analysis and imperfection sensitivity of porous FG micro-tubes surrounded by a nonlinear softening elastic medium

An imperfection sensitivity analysis for the nonlinear post-buckling behavior of functionally graded (FG) porous micro-tubes is performed in this research. The case of geometrically imperfect micro-tubes surrounded by a nonlinear elastic medium under axial compressive load is analyzed. Properties of the micro-tube with uniform distributed porosity are FG across the radius of the cross-section. Two types of boundary conditions as simply-supported and clamped are considered. The high-order shear deformation theory of tubes is utilized to approximate the displacement field. Differential equations governing the equilibrium position of the micro-tube are extracted using the virtual displacement principle. These nonlinear equations are analytically solved by means of the two-step perturbation technique and Galerkin procedure. It is shown that when the imperfect micro-tube is in contact with a sufficiently soft foundation, the post-buckling path of the structure is unstable, and therefore the structure is imperfection sensitive. Since the imperfection sensitivity of micro-tubes is not reported in literature, results of this study are compared with buckling responses of perfect FGM tubes. The effects of porosity coefficient, power law index, length scale parameter, and geometrical parameters upon the limit buckling load of imperfect micro-tubes are investigated.

Porous microtubes of nickel-cobalt double oxides as non-enzymatic hydrogen peroxide sensors

Non-enzymatic electrochemical sensors for the determination of hydrogen peroxide (H2O2) have attracted more and more concerns. A series of nickel and cobalt double oxides (NixCoy-DO) with the different ratios of Ni/Co have been prepared by a polyol-mediated solvothermal method for H2O2 detection. The obtained products exhibit honeycomb-like open porous microtubes constituted with the low-dimensional nanostructured NixCoy-DO blocks after the calcination treatment. Compared with nickel oxides, the introduced Co ions in NixCoy-DO can induce the production of surficial oxygen vacancies, and further enhance the electrode surface activity. In particular, the NiCo-DO sample (with an atomic ratio of Ni/Co = 4:3) shows the richest surficial oxygen vacancies and presents the highest H2O2 detection activity among all the as-prepared samples, demonstrating an excellent sensitivity of 698.60 μA L mmol−1 cm-2 (0 ∼ 0.4 mmol/L), low detection limit (0.28 μmol/L, S/N = 3), as well as long stability, high selectivity and good reproducibility. This work lends a new impetus to the potential application of double metal oxides for the next generation of non-enzymatic sensors.

Nonlinear bending analysis of size-dependent FG porous microtubes in thermal environment based on modified couple stress theory

This study deals with the nonlinear bending analysis of elastic tubes made of functionally graded (FG) porous material based on modified couple stress theory. Immovable simply supported and clamped boundary conditions are assumed for the FG porous microtubes resting on nonlinear elastic foundation. Transverse pressure load is applied uniformly on the upper surface of the microtube which is exposed to uniform temperature field. Temperature-dependent material properties of the microtube with uniformly distributed porosity are graded across the radius of the cross-section. The higher-order shear deformation theory of circular beams is presented to approximate the displacement field. The von Kármán type of kinematic assumptions is utilized for nonlinear strain-displacement relations. The uncoupled thermoelasticity theory is used to derive the constitutive equations. With the establishment of the virtual displacement principle, nonlinear differential equations governing the equilibrium position of the microtube are extracted. These equilibrium equations are analytically solved by means of the two-step perturbation technique and Galerkin procedure. Parametric investigations are performed to demonstrate the size-dependent nonlinear bending responses of an FG porous microtube on nonlinear elastic foundation in thermal environment.

Size-dependent vibrations of thermally pre/post-buckled FG porous micro-tubes based on modified couple stress theory

Based on the modified couple stress theory, an analytical approach is presented to study vibrations of thermally pre/post-buckled functionally graded (FG) tubes. The case of simply supported FG micro-tubes with uniform distributed porosity surrounded by nonlinear elastic medium in uniform temperature field is analyzed. Thermomechanical properties are functionally graded across the radius of cross-section of the tube by means of a power law function. The traction free boundary conditions on the inner and outer surfaces of the structure are satisfied. Basic formulations are constructed using the higher-order shear deformation tube theory and the von Kármán type of nonlinear strain-displacement relationships. The governing equations of motion are derived using the Hamilton principle. The dimensionless equations of motion are solved analytically by employing the two-step perturbation technique and the Galerkin procedure. An explicit closed-form solution is obtained to analyze the size-dependent linear and nonlinear free vibrations of micro-tubes in thermal environment. The numerical results are verified by comparison with the existing data in literature for tubes without couple stress effect. Novel numerical results are revealed in the parametric studies to show the large amplitude vibration responses of thermally pre/post-buckled FG porous micro-tubes. The effects of microstructural length scale parameter, functionally graded patterns, porosity distribution parameter, nonlinear elastic foundation, temperature dependence, and geometrical properties of the structure are investigated.

Enhancing the red upconversion luminescence of hybrid porous microtubes via an in situ O-substituted reaction through heat treatment

Uniform NaYF4:Yb/Er@YOF:Yb/Er porous microtubes with single-band red emission have been synthesized via a hydrothermal approach followed by an annealing treatment, which provides potential opportunities for anti-counterfeiting applications.