Multiple Engineering Applications Research Articles

Plasma treatment effects on bulk properties of polycaprolactone nanofibrous mats fabricated by uncommon AC electrospinning: A comparative study

The prominent success of polycaprolactone (PCL) electrospun nanofibrous mats (ENM) has expanded the use of PCL over other polymers for tissue engineering applications. However, the major challenge in the design of a nanofibrous scaffold is to modify its surface properties while preserving its bulk properties. Therefore, the first part of the study is focused on the fabrication of PCL-ENMs by alternating-current electrospinning using the following solvent systems: formic acid, formic acid/acetic acid (1/1) and formic acid/acetic acid/acetone (1/1/1). While the second part is focused on an nm-thick surface chemical modification via medium pressure argon and nitrogen plasma treatment, and the third part is dedicated to investigating the morphology, wettability, surface functional groups, crystallite size, crystallinity, crystallization, and melting temperature of plasma-treated nanofibers. Samples were characterized using scanning electron microscopy (SEM), water contact angle analysis (WCA), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and differential scanning calorimetry (DSC). WCA and SEM results showed that plasma treatments significantly improve the wettability of the PCL ENMs without compromising their surface morphology. XPS analysis revealed that argon and nitrogen gases are responsible for a substantial increase in polar oxygen and nitrogen functional groups respectively. Out of the six plasma-treated PCL ENMs understudy, the argon plasma-treated sample showed superior hydrophilicity (from 136° to ~35°) followed by nitrogen plasma treatment (from 136° to ~42°). It was also found from XRD that the crystallite size was not significantly affected by the conducted plasma treatments. Moreover, the degree of crystallinity was also not altered by the plasma treatments, as was observed by DSC and FTIR. The conducted experiments showed that the surface properties of the PCL ENMs could be positively affected while maintaining their beneficial bulk properties thereby making these plasma-modified ENMs excellent candidates in multiple biomedical and tissue engineering applications.

Earwig fan designing: Biomimetic and evolutionary biology applications

Technologies to fold structures into compact shapes are required in multiple engineering applications. Earwigs (Dermaptera) fold their fanlike hind wings in a unique, highly sophisticated manner, granting them the most compact wing storage among all insects. The structural and material composition, in-flight reinforcement mechanisms, and bistable property of earwig wings have been previously studied. However, the geometrical rules required to reproduce their complex crease patterns have remained uncertain. Here we show the method to design an earwig-inspired fan by considering the flat foldability in the origami model, as informed by X-ray microcomputed tomography imaging. As our dedicated designing software shows, the earwig fan can be customized into artificial deployable structures of different sizes and configurations for use in architecture, aerospace, mechanical engineering, and daily use items. Moreover, the proposed method is able to reconstruct the wing-folding mechanism of an ancient earwig relative, the 280-million-year-old Protelytron permianum This allows us to propose evolutionary patterns that explain how extant earwigs acquired their wing-folding mechanism and to project hypothetical, extinct transitional forms. Our findings can be used as the basic design guidelines in biomimetic research for harnessing the excellent engineering properties of earwig wings, and demonstrate how a geometrical designing method can reveal morphofunctional evolutionary constraints and predict plausible biological disparity in deep time.

Manufacturing carbon fibres from pitch and polyethylene blend precursors: a review

Carbon fibres are one of the newer, emerging materials with multiple engineering applications, from automobiles to space vehicles. Carbon fibres have high mechanical strength, are lighter than metals with better chemical resistance.There have been reports on the use of polyethylene and pitch precursors for the production of carbon fibres, but there are few reports of how these blends could be used for carbon fibre preparation. Bearing in mind the myriad of benefits that using carbon fibres could bring, this paper reviews recent advances published in the literature on how mesophase pitch and polyethylene could be suitable precursors for carbon fibres. It also provides an introduction to the development of precursor blends that allow the properties of carbon fibres to be tailored to specific applications, including processing techniques, fibre parameters, fibre properties and fibre structure.

Rapid conjunction of 1D carbon nanotubes and 2D graphitic carbon nitride with ZnO for improved optoelectronic properties

Conjunction of 1D as well as 2D carbonaceous materials (CMs) is of great importance because of the significant improvement in the optoelectronic properties. Through extensive optimization, a rapid, facile and heat-treatment free route is progressed which ensues 88.4 and 92.3% degradation of congo-red dye for CNTs/ZnO and g-C3N4/ZnO, respectively. g-C3N4/ZnO shows the highest value of correlation co-efficient (R2) (0.9927) and rate constant (KC) (0.0390 min−1) among all others. g-C3N4/ZnO-HPs4 displays the highest potential of 1.54 V and over potential of 310 mV for current density value of 10 mA/cm2 compared to others composite while CNTs/ZnO-HPs4 Tafel slope has a value of 42 mV/dec. Scanning and transmission electron microscopy, X-ray diffractometry and energy dispersive spectrometry were carried out to confirm the efficacy of nano-composites while electron LSV, Tafel slopes and Nyquist plots were plotted to reveal the consequent efficient electro-catalytic behavior. The modified recipe for the development of nanocomposites having CMs exhibited its potential for use in multiple engineering applications, including but not limited to photocatalysis and oxygen evolution reaction.

Measurement of thermal conductivity of millimeter-sized wires using the fin effect

Measurement of thermal conductivity of thin wires is critical for multiple engineering applications that involve heat transfer in thin wires. While well-established experimental methods are available for thermal conductivity measurements on large as well as microscale samples, these methods do not work well for thin wires of around a few mm diameter. This paper presents a comparative method for measuring thermal conductivity of a thin wire. The method is based on infrared thermography of the wire of interest suspended from a high temperature base. Through comparison of thermal response of the wire with that of a standard wire of known properties, thermal conductivity is measured for a number of wires in a broad range of thermal conductivity. Measurements are reported for both low thermal conductivity polymer wires and high thermal conductivity metal wires. Results are found to be in good agreement with expected values of thermal conductivity. The effect of wire diameter and base temperature on the accuracy of measurements is investigated. The method is used for measurement of thermal conductivity of solder wires. Results presented in this work contribute towards addressing an important thermal metrology need, and may help improve thermal design of a broad range of engineering applications that utilize thin wires.

Response of a turbulent boundary layer to rapid freestream acceleration

In a wide range of fluid machinery, a turbulent boundary layer can be exposed to rapid transients of the freestream conditions. A simplified model of the boundary layer response would provide valuable guidance in understanding these situations in multiple engineering applications. To this end, a turbulent boundary flow, subject to freestream acceleration, was explored through high-fidelity simulations and Reynolds-averaged Navier–Stokes calculations. Test cases were considered in which the flow over a flat plate accelerated from Mach 0.3 up to 0.6 over two time scales, 10 ms and 25 ms. Based on data from the calculations, the integral boundary layer momentum equation was simplified to propose a new reduced-order model capable of computing the evolution of the boundary layer under external flow transients. Given the initial boundary layer height, and the temporal evolution of the freestream pressure, velocity, and density, the model predicts the transient development of the boundary layer. With the transient boundary layer profile known, the temporal history of the skin friction and heat transfer can be predicted, taking advantage of standard shear stress correlations and the Reynolds analogy.

A novel crosslinker-free technique toward the fabrication of collagen microspheres.

Injectable collagen microspheres (CMs) have the potential to be an excellent tool to deliver various modulatory agents or to be used as a cellular transporter. A drawback has been the difficulty in producing reliable and spherical CMs. A crosslinker-free method to fabricate CMs was developed using liquid collagen (LC) in a water-in-oil emulsion process with varying concentrations of surfactant span-80. Different emulsion times of up to 16-hr were utilized to produce the CMs. Visual microscopy and scanning electron microscopy were utilized to determine the morphology of the CMs. To determine the fibril nature of the CMs, focus ion beam milling, energy dispersive spectroscopy, and Fourier Transformation-Infrared spectroscopy were performed. A cell biocompatibility study was performed to assess the biocompatibility of the CMs. The results demonstrated that consistent spherical CMs were achievable by changing the span-80 concentration. The CMs were fibrilized not only at the surface, but also at the core. Both the 1- and 16-hr emulsion time demonstrated biocompatibility and it appeared that the cells preferentially adhered to the CMs. This crosslinker-free method to fabricate CMs resulted in spherical, stable, biocompatible CMs, and could be an excellent technique for multiple tissue engineering applications.

Versatile Biomaterial Platform Enriched with Graphene Oxide and Carbon Nanotubes for Multiple Tissue Engineering Applications.

Carbon-based nanomaterials, such as graphene oxide (GO) or carbon nanotubes (CNTs) are currently used in various medical applications due to their positive influence on biocompatibility, adhesion, proliferation, and differentiation, as well as their contribution to modulating cell behavior in response to nanomaterial substrates. In this context, in this study, novel flexible membranes based on cellulose acetate (CA) enriched with CNT and GO in different percentages were tested for their versatility to be used as substrates for soft or hard tissue engineering (TE), namely, for their ability to support human adipose-derived stem cells (hASCs) adhesion during adipogenic or osteogenic differentiation. For this purpose, differentiation markers were assessed both at gene and protein levels, while histological staining was performed to show the evolution of the processes in response to CA-CNT-GO substrates. Micro-CT analysis indicated porous morphologies with open and interconnected voids. A slightly lower total porosity was obtained for the samples filled with the highest amount of GO and CNTs, but thicker walls, larger and more uniform pores were obtained, providing beneficial effects on cell behavior and increased mechanical stability. The addition of 1 wt% GO and CNT to the biocomposites enhanced hASCs adhesion and cytoskeleton formation. The evolution of both adipogenic and osteogenic differentiation processes was found to be augmented proportionally to the GO-CNT concentration. In conclusion, CA-CNT-GO biomaterials displayed good properties and versatility as platforms for cell differentiation with potential as future implantable materials in TE applications.

Vitrified Wharton’s jelly tissue as a biomaterial for multiple tissue engineering applications

Wharton’s Jelly (WJ) tissue is a promising biomaterial, for tissue engineering applications. However, its preservation over a long period in order to be readily available needs further optimization. A possible solution could be the vitrification and storage of WJ tissue at low temperatures. The aim of this study is to evaluate the effect of low temperature in the WJ tissue, which was stored at −196 °C, either with the vitrification or conventional cryopreservation methods. WJ tissues were isolated from human umbilical cords, cryopreserved with the above methods and remained for 1 year at −196 °C. Histological analysis of tissue’s extracellular matrix (ECM), isolation, and characterization of mesenchymal stromal cells (MSCs) were performed. Histological analysis revealed the presence of ECM components such as collagen, sulfated glycosaminoglycans (sGAGs), and the presence of cell nuclei only in vitrified samples. Furthermore, MSCs were isolated and expanded successfully from vitrified WJ tissues, whereas a few viable cells were obtained from conventionally cryopreserved tissues that were not further expanded. In conclusion, this study indicated the proper preservation of vitrified WJ tissues after 1 year of storage, which eventually could be used in tissue engineering and regenerative medicine approaches.

SFOPDES: A Stepwise First Order Partial Differential Equations Solver with a Computer Algebra System

Partial Differential Equations (PDE) appear in multiple Physic and Engineering applications. Normally, when modeling an application, the use of well-known and already solved PDE is considered. But what happens if a new PDE is used? Solving a new PDE is not an easy task. In this paper, we use a Computer Algebra System (Cas) in order to find the solution of PDE of first order.Specifically, we deal with Pfaff Equations, Quasilinear PDE and general first order PDE (using Lagrange–Charpit Method).To solve these PDE, we combine the power of a Cas with the flexibility of programming with it. Furthermore, the developed programs do not only provide the final result but also display all the intermediate steps which lead to find the solution of the PDE. This way, we introduce SFOPDES, a new Stepwise First Order PDE Solver which serves as a tutorial showing, step by step, the way to deal with PDE.

Synergetic effect of electrospun PCL fiber size, orientation and plasma-modified surface chemistry on stem cell behavior

Electrospun polymeric meshes have revolutionized the evolving tissue engineering field for their extracellular matrix mimicry. However, besides the fibrous architecture, cell-material interactions are also critically and synergistically influenced by specific surface chemical and topographical features, such as fiber size and fiber orientation. To examine these effects in detail, random polycaprolactone (PCL) fibers with average diameters of 232, 500 and 1272 nm and highly aligned fibers with diameters of 225, 482 and 1173 nm are electrospun in this work. Surface biofunctionalization is then achieved by plasma-treating the fibers using argon at medium pressure. Results reveal a significantly enhanced wettability on plasma-treated fibers due to the incorporation of oxygen-containing functionalities on their surface. A treatment time of 15 s is shown to preserve the scale and morphology of all fiber conditions. However, an extended plasma exposure starts damaging the fibers with a growing risk of drastic alterations on thicker and random fibers compared to thinner and aligned fibers. These diverse responses stem from the distinct molecular chain arrangement and crystallinity of different fiber sizes and orientations. The fibers bioresponsive properties are also profoundly investigated in this study by seeding and evaluating adipose-derived stem cells (ADSCs) performance. Plasma treatment strikingly enhances the cell metabolic activity, adhesion, proliferation and cytoplasmic remodeling on all samples. Cells adhere multi-directionally on random fibers with a gradual change from dilated and more circular to a stretched out and more elongated shape on increasing diameters. In contrast, ADSCs overextend in a bipolar and aligned fashion on aligned fibers with a tendency to attach on fewer fibers with increasing fiber diameter. A critical distinction is the cell infiltration in-between the pores of the thickest fibers. Overall, plasma-treated fibers are very promising substrates for multiple tissue engineering applications. Since the desired ADSCs behavior observed on distinct fiber size and orientation strongly depends on a specific end-application, this work constitutes a picture-perfect reference paving the way towards the optimization of the previous generation of scaffolds.

Thermo-Hydro-Mechanical Modeling of Artificial Ground Freezing: Application in Mining Engineering

For decades, artificial ground freezing (AGF) has been used as a temporary soil stabilization and waterproofing technique in multiple geotechnical engineering applications. Experience gained from AGF experiments indicates that the pore water expansion during freezing and the resulting pressure have the potential to induce ground movements in adjacent nonfrozen areas. This process was investigated in this paper using a comprehensive set of in situ temperature and displacement monitoring data collected in the Cigar Lake underground mine, Canada. The data set allowed to investigate the mechanical impact of freezing on a mine tunnel and prompted the need to derive a fully coupled thermo-hydro-mechanical model to predict ground temperature and displacements. Thermodynamically consistent, the model developed for this study is based on a macroscopic continuum approach and uses simplifying assumptions to overcome the computational difficulties associated with the modeling of complex mining environments over a long period of time. This model was used to perform three-dimensional finite-element simulations of the ground freezing and excavation activities in the Cigar Lake mine, showing good agreement with field measurements.

Theoretical modeling of a phase change heat transfer problem with a pre-melted or pre-solidified region

Heat transfer problems involving phase change occur in a wide variety of engineering applications. Except a few simple cases, most phase change problems do not have an exact solution, and a number of approximate analytical methods have been developed. This paper presents a theoretical solution for a one-dimensional phase change problem that includes a pre-melted or pre-solidified length between the region of interest and a time-dependent temperature boundary condition. Such a scenario can occur in multiple engineering applications when the heating or cooling process is intermittent in time. The theoretical approach involves iteratively solving the coupled problem involving thermal conduction and phase change, utilizing a perturbation-based method for the phase change problem with a time-dependent boundary condition. The resulting theoretical solution compares well with numerical simulations. Results are used for analyzing the effect of geometry, thermal properties and other parameters on the nature of heat transfer and phase change in this problem of much technological importance. These insights may be helpful in analyzing and optimizing heat transfer in several applications such as phase change based cooling of Li-ion cells during intermittent operation.

Material properties of normal and high strength aluminium alloys at elevated temperatures

Aluminium alloys are being used widely in multiple engineering applications. However, the material properties of aluminium alloys could change significantly at high temperatures. This paper studied the mechanical properties of normal strength aluminium alloy 6063-T5 and high strength aluminium alloy 6061-T6 at elevated temperatures. Tensile tests were conducted at room temperature (24 °C) and high temperatures up to 600 °C. Both steady temperature state tests and transient temperature state tests were used. The yield stress (i.e., 0.2% proof stress), the ultimate stress, the Young's modulus, and the ultimate strain were determined from tests. The measured material properties at different temperatures are compared with the predictions by the American and European specifications. A series of unified equations for calculating the reduction factors of the material properties at high temperatures are proposed herein; they are found to yield more accurate reduction factors for aluminium alloys.

Potential use of activated Algerian natural pozzolan powder as a cement replacement material

The purpose of this experimental work is to develop a suitable approach for an alkali-activated binder material to replace cement CEM-II/42.5 by 80% of natural pozzolan. The chemical activity of silica and alumina found in Algeria's natural pozzolan is improved using heat treatment and chemical curing, together with several alkali activators, including a 6-mole NaOH and a 6-mole KOH along with CaCl2, Na2SO4 and Na2SiO3. The chemical and morphological processes are monitored using X-ray diffraction, TGA and DTA, as well as particle size distribution analyses. Laboratory tests show that thermal pretreatment positively affects the compressive strength; moreover, the use of 6% Na2SiO3 and 6% Na2SO4 results in increased short-term and long-term compressive strength, respectively. Optimal compressive strength values are reached under chemical activation and thermal pretreatment processes. These combined processes also affect Young's modulus values and the relative deformations caused by ultimate stresses. This experimental work highlights the potential of natural pozzolan in producing an economical and environmentally-friendly sustainable material that can be substituted for Portland cements and used in multiple engineering applications.

Solution of the Phase Change Stefan Problem With Time-Dependent Heat Flux Using Perturbation Method

Theoretical understanding of phase change heat transfer problems is of much interest for multiple engineering applications. Exact solutions for phase change heat transfer problems are often not available, and approximate analytical methods are needed to be used. This paper presents a solution for a one-dimensional (1D) phase change problem with time-dependent heat flux boundary condition using the perturbation method. Two different expressions for propagation of the phase change front are derived. For the special case of constant heat flux, the present solution is shown to offer key advantages over past papers. Specifically, the present solution results in greater accuracy and does not diverge at large times unlike past results. The theoretical result is used for understanding the nature of phase change propagation for linear and periodic heat flux boundary conditions. In addition to improving the theoretical understanding of phase change heat transfer problems, these results may contribute toward design of phase change based thermal management for a variety of engineering applications, such as cooling of Li-ion batteries.

The Promise of Sustainable Magnesium Composite Technology for Greener Future

Ethical research that ensures the enhancement of quality of human life for present and future generations is the need of the day. This inherits the typical requirement to impose zero or minimal stress on the environment. Currently, planet earth is witnessing global warming and largely unpredictable weather changes, primarily due to greenhouse gas emissions. Transportation sector is one of the major engineering sectors contributing to greenhouse gas emissions. One way to mitigate/minimize these emissions is to use lightweight materials in the construction of vehicles for use in land, water, aerospace and space applications. Towards this, magnesium based materials are viable options which are suitable to replace aluminum based materials allowing ~ 35% weight saving on a component basis. As magnesium is abundant in nature and is a nutritional element, its availability and recyclability is not an issue. Accordingly, this paper will focus on the development of magnesium based nanocomposites capable of replacing conventional materials in multiple engineering and biomedical applications.

Graphene dispersion in a surfactant-free, polar solvent

Here, we demonstrate dispersion of graphene nanoplatelets (GNPs) in ethylene glycol (EG), a polar dispersion medium, by a liquid-phase exfoliation method involving sonication and centrifugation. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy are used for qualitative and quantitative characterization of the graphene dispersions. TEM micrographs confirm the exfoliation and production of monolayer GNPs after sonication. Statistical analysis of TEM micrographs shows that increasing the sonication time increases the degree of exfoliation of GNPs. Raman spectroscopy studies also show that high-power probe sonication exfoliates multi-layer GNPs to few-layer GNPs. The proposed method is promising to provide monolayer and few-layer graphene dispersed in a polar medium, practical to multiple engineering applications including polymer nanocomposites.

Remote Sensing to Estimate Saturation Differences of Chosen Building Materials Using Terrestrial Laser Scanner

Abstract Terrestrial Laser Scanner (TLS) method which is commonly used for geodetic applications has a great potential to be successfully harnessed for multiple civil engineering applications. One of the most promising uses of TLS in construction industry is remote sensing of saturation of building materials. A research programme was prepared in order to prove that harnessing TLS for such an application is viable. Results presented in the current paper are a part of a much larger research programme focused on harnessing TLS for remote sensing of saturation of building materials. The paper describes results of the tests conducted with an impulse scanner Leica C-10. Tests took place both indoors (in a stable lab conditions) and outdoors (in a real environment). There were scanned specimens of the most popular building materials in Europe. Tested specimens were dried and saturated (including capillary rising moisture). One of the tests was performed over a period of 95 hours. Basically, a concrete specimen was scanned during its setting and hardening. It was proven that absorption of a laser signal is influenced by setting and hardening of concrete. Outdoor tests were based on scanning real buildings with partially saturated facades. The saturation assessment was based on differences of values of intensity. The concept proved to be feasible and technically realistic.

High Performance Magnesium Based Composites Containing Nano-Length Scale/Amorphous/Hollow Reinforcements

Magnesium is the lightest weight metallic material that can be used in multiple engineering applications and biomedical sector as a structural material. It is abundantly available in earth’s crust and sea water and non-toxic in nature. Inherent to magnesium is its superior specific mechanical properties, high damping, electromagnetic shielding capability and ability to reduce carbon signature of the transportation sector.Magnesium is one of the widely available metal in earth crust and sea water. It is non-toxic and hence does not pose a health risk during recycling or waste dumping in natural water bodies. As a result, magnesium technology is sustainable and beneficial to planet earth and living organisms.Magnesium based materials are gradually being used in many applications and their performance and applications can further be stretched using the composite technology. Accordingly, the main scope of this paper is to highlight the enhancement of a number of properties of magnesium through the use of nanolength scale, amorphous and hollow reinforcements.