Synthesis, characterization, and antimicrobial properties of novel double layer nanocomposite electrospun fibers for wound dressing applications

Herein, novel hybrid nanomaterials were developed for wound dressing applications with antimicrobial properties. Electrospinning was used to fabricate a double layer nanocomposite nanofibrous mat consisting of an upper layer of poly(vinyl alcohol) and chitosan loaded with silver nanoparticles (AgNPs) and a lower layer of polyethylene oxide (PEO) or polyvinylpyr- rolidone (PVP) nanofibers loaded with chlorhexidine (as an antiseptic). The top layer containing AgNPs, whose purpose was to protect the wound site against environmental germ invasion, was prepared by reducing silver nitrate to its nanoparticulate form through interaction with chitosan. The lower layer, which would be in direct contact with the injured site, contained the antibi- otic drug needed to avoid wound infections which would otherwise interfere with the healing process. Initially, the upper layer was electrospun, followed sequentially by electrospinning the second layer, creating a bilayer nanofibrous mat. The morphology of the nanofibrous mats was studied by scanning electron microscopy and transmission electron microscopy, showing successful nanofiber production. X-ray diffraction confirmed the reduction of silver nitrate to AgNPs. Fourier transform infrared spectroscopy showed a successful incorporation of the material used in the produced nanofibrous mats. Thermal studies carried out by thermogravi- metric analysis indicated that the PVP–drug-loaded layer had the highest thermal stability in comparison to other fabricated nanofibrous mats. Antimicrobial activities of the as-synthesized nanofibrous mats against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans were determined using disk diffusion method. The results indicated that the PEO–drug-loaded mat had the highest antibacterial activity, warranting further attention for numerous wound-healing applications.QUST-CAS-SPR-14\15-

Numerical study of the noninertial systems: applicationto train coupler systems

Car coupler forces have a significant effect on the longitudinal train dynamics and stability. Because the coupler inertia is relatively small in comparison with the car inertia; the high stiffness associated with the coupler components can lead to high frequencies that adversely impact the computational efficiency of train models. The objective of this investigation is to study the effect of the coupler inertia on the train dynamics and on the computational efficiency as measured by the simulation time. To this end, two different models are developed for the car couplers; one model, called the inertial coupler model, includes the effect of the coupler inertia, while in the other model, called the noninertial model, the effect of the coupler inertia is neglected. Both inertial and noninertial coupler models used in this investigation are assumed to have the same coupler kinematic degrees of freedom that capture geometric nonlinearities and allow for the relative translation of the draft gears and end of car cushioning (EOC) devices as well as the relative rotation of the coupler shank. In both models, the coupler kinematic equations are expressed in terms of the car body and coupler coordinates. Both the inertial and noninertial models used in this study lead to a system of differential and algebraic equations that are solved simultaneously in order to determine the coordinates of the cars and couplers. In the case of the inertial model, the coupler kinematics is described using the absolute Cartesian coordinates, and the algebraic equations describe the kinematic constraints imposed on the motion of the system. In this case of the inertial model, the constraint equations are satisfied at the position, velocity, and acceleration levels. In the case of the noninertial model, the equations of motion are developed using the relative joint coordinates, thereby eliminating systematically the algebraic equations that represent the kinematic constraints. A quasistatic force analysis is used to determine a set of coupler nonlinear force algebraic equations for a given car configuration. These nonlinear force algebraic equations are solved iteratively to determine the coupler noninertial coordinates which enter into the formulation of the equations of motion of the train cars. The results obtained in this study showed that the neglect of the coupler inertia eliminates high frequency oscillations that can negatively impact the computational efficiency. The effect of these high frequencies that are attributed to the coupler inertia on the simulation time is examined using frequency and eigenvalue analyses. While the neglect of the coupler inertia leads, as demonstrated in this investigation, to a much more efficient model, the results obtained using the inertial and noninertial coupler models show good agreement, demonstrating that the coupler inertia can be neglected without having an adverse effect on the accuracy of the solutio

Eco-friendly highly efficient BN/rGO/TiO2 nanocomposite visible-light photocatalyst for phenol mineralization

Boron nitride (BN) and reduced graphene oxide (rGO) of different loadings were composited with commercial P25 TiO2 (Ti) through the hydrothermal method. The as-prepared nanocomposites were characterized using various techniques: X-ray photoelectron spectroscopy, X-ray diffraction, thermal gravimetric analysis, Fourier transform infrared and Raman spectroscopies, and transmission and scanning electron microscopies. It was observed that 10% and 0.1% of BN and rGO, respectively, loaded on TiO2 (10BNr0.1GOTi) resulted in the best nanocomposite in terms of phenol degradation under simulated sunlight. A 93.4% degradation of phenol was obtained within 30 min in the presence of H2O2. Finally, to ensure the safe use of BNrGOTi nanoparticles in the aquatic environment, acute zebrafish toxicity (acutoxicity) assays were studied. The 96-h acute toxicity assays using the zebrafish embryo model revealed that the LC50 for the BNrGOTi nanoparticle was 677.8 mg L−1 and the no observed effect concentration (NOEC) was 150 mg L−1. Therefore, based on the LC50 value and according to the Fish and Wildlife Service Acute Toxicity Rating Scale, BNrGOTi is categorized as a “practically not toxic” photocatalyst for water treatment.Open access funding provided by the Qatar National Library. This work was supported by the Qatar National Research Fund (QNRF, a member of the Qatar Foundation) through the National Priority Research Program Grant (NPRP) NPRP13S-0117-200095. Also, this publication was supported by Qatar University ' s internal grant IRCC-2021-015. Statements made herein are solely the responsibility of the authors

Use of Non-inertial Coordinates and Implicit Integration for Efficient Solution of Multibody Systems

Development of computational methods, formulations, and algorithms to study interconnected bodies that undergo large deformation, translational, and rotational displacements is the main focus for this thesis. This thesis discusses the use of the concept of non-inertial coordinates and implicit numerical integrations methods to solve stiff MBS differential/algebraic equations. Complex MBS examples that consist of rigid and flexible bodies are used as examples in order to demonstrate the use of these developed algorithms. One of the main contributions of this thesis is to employ the concept of the inertial and non-inertial coordinates to obtain an efficient solution for practical MBS applications. Inertial coordinates have generalized inertia forces associated with them, while the non-inertial coordinates have no generalized inertia forces. In order to avoid having a singular inertia matrix and/or high frequency oscillations, the second derivatives of the non-inertial coordinates are not used when formulating the system equations of motion in this study. In this case, the system coordinates are partitioned into two distinct sets; inertial and non-inertial coordinates. The use of the principle of virtual work leads to a coupled system of differential and algebraic equations expressed in terms of the inertial and non-inertial coordinates. The differential equations are used to determine the inertial accelerations which can be integrated to determine the inertial coordinates and velocities. The non-inertial coordinates are determined by using an iterative algorithm to solve a set of nonlinear algebraic force equations obtained using quasi-static equilibrium conditions. The non-inertial velocities are determined by solving these algebraic force equations at the velocity level. The non-inertial coordinates and velocities enter into the formulation of the generalized forces associated with the inertial coordinates. Using the concept of non-inertial coordinates and the resulting differential/algebraic equations obtained in this thesis leads to significant reduction in the numbers of state equations, system inertial coordinates, and constraint equations; and allows avoiding a system of stiff differential equations that can arise because of the relatively small mass. The development of accurate nonlinear longitudinal train force models is necessary in order to better understand railroad vehicle dynamic scenarios that include braking, traction, and derailments. Car coupler forces have significant effects on the longitudinal train dynamics and stability. Using the concept of non-inertial coordinate developed in this thesis allows developing of a more detailed coupler model that captures the coupler kinematics without significantly increasing the number of state equations and the dimension of the problem. The coupler model proposed in this thesis allows for the car bodies to have arbitrary displacements, also avoids having a stiff system of differential equations that can result from the use of relatively small masses. In order to in order to examine the efficiency of using the concept of non-inertial coordinates, a comparative study of the inertial and non-inertial coordinate coupler models is conducted. The dynamics of large and complex multibody systems that include flexible bodies and contact/impact pairs is governed by stiff equations. Explicit integration methods can be very inefficient and often fail in the case of stiff problems. The use of implicit numerical integration methods is recommended in this case. To this end, the thesis presents a new and efficient implementation of the two-loop implicit sparse matrix numerical integration (TLISMNI) method proposed for the solution of constrained rigid and flexible multibody system (MBS) differential and algebraic equations. Another contribution of this thesis is to integrate the Newton-Krylov projection method in a MBS algorithm based on two-loop implicit sparse matrix numerical integration (TLISMNI) procedure with the goal to improve the efficiency and robustness of the TLISMNI method when used for the numerical solution of constrained complex rigid and flexible MBS differential and algebraic equations. The simple iterations and Jacobian-Free Newton-Krylov approaches are used in the TLISMNI implementation. The TLISMNI method does not require numerical differentiation of the forces, allows for an efficient sparse matrix implementation, and ensures that the algebraic constraint equations are satisfied at the position, velocity, and acceleration levels. In the augmented formulation and recursive method used in this investigation, the constraint equations are satisfied at all levels. Different low order integration formulas such as HHT, which includes numerical damping, Park, Trapezoidal, and BDF2 methods were used and recommendations on the appropriateness of each method for a particular problem are made. TLISMNI implementation issues including step size selection, convergence criteria, the error control, and effect of the numerical damping were discussed. Simple pendulum, complex rigid and flexible tracked vehicle, and railroad vehicle models were used to demonstrate the use of the proposed TLISMNI method. A comparison between the results obtained using the TLISMNI algorithm and the explicit Adams predictor-corrector method is presented and show good agreement. On the other hand, using TLISMNI method which does not require numerical differentiation of the forces and allows for an efficient sparse matrix implementation for solving complex and very stiff structure problems significantly improves the simulation time. For the rigid body model considered in this investigation, the TLISMNI is at least five times faster than the explicit Adams method. Using the TLISMNI algorithm with integration formulas that employ numerical damping such as HHT in the simulation of- the flexible body models considered in this study can achieve up to thirty five times faster simulation compared to Adams method. Nonetheless, it is important to mention that there are cases of non-stiff problems in which the use of explicit Adams method can be more efficient than the TLISMNI methods. The use of the Jacobian-Free Newton-Krylov approach instead of the simple iteration approach improves the convergence and accuracy of the TLSMNI method

Efficient and robust implementation of the TLISMNI method

The dynamics of large scale and complex multibody systems (MBS) that include flexible bodies and contact/impact pairs is governed by stiff equations. Because explicit integration methods can be very inefficient and often fail in the case of stiff problems,the use of implicit numerical integration methods is recommended in this case. This paper presents a new and efficient implementation of the two-loop implicit sparse matrix numerical integration (TLISMNI) method proposed for the solution of constrained rigid and flexible MBS differential and algebraic equations. The TLISMNI method has desirable features that include avoiding numerical differentiation of the forces, allowing for an efficient sparse matrix implementation, and ensuring that the kinematic constraint equations are satisfied at the position, velocity and acceleration levels. In this method, a sparse Lagrangian augmented form of the equations of motion that ensures that the constraints are satisfied at the acceleration level is used to solve for all the accelerations and Lagrange multipliers. The generalized coordinate partitioning or recursive methods can be used to satisfy the constraint equations at the position and velocity levels. In order to improve the efficiency and robustness of the TLISMNI method, the simple iteration and the Jacobian-Free Newton-Krylov approaches are used in this investigation. The new implementation is tested using several low order formulas that include Hilber–Hughes–Taylor (HHT), L- stable Park, A-stable Trapezoidal, and A-stable BDF methods. The HHT method allow for including numerical damping. Discussion on which method is more appropriate to use for a certain application is provided. The paper also discusses TLISMNI implementation issues including the step size selection, the convergence criteria, the error control, and the effect of the numerical damping. The use of the computer algorithm described in this paper is demonstrated by solving complex rigid and flexible tracked vehicle models, railroad vehicle models, and very stiff structure problems. The results, obtained using these low order formulas, are compared with the results obtained using the explicit Adams-Bashforth predictor-corrector method. Using the TLISMNI method, which does not require numerical differentiation of the forces and allows for an efficient sparse matrix implementation, for solving complex and stiff structure problems leads to significant computational cost saving as demonstrated in this paper. In some problems, it was found that the new TLISMNI implementation is 35 times faster than the explicit AdamsBashforth method

Carbon Dioxide Methanation Enabled by Biochar-Nanocatalyst Composite Materials: A Mini-Review

Due to ever-increasing global warming, the scientific community is concerned with finding immediate solutions to reduce or utilize carbon dioxide (CO2) and convert it in useful compounds. In this context, the reductive process of CO2 methanation has been well-investigated and found to be attractive due to its simplicity. However, it requires the development of highly active catalysts. In this mini-review, the focus is on biochar-immobilized nanocatalysts for CO2 methanation. We summarize the recent literature on the topic, reporting strategies for designing biochar with immobilized nanocatalysts and their performance in CO2 methanation. We review the thermochemical transformation of biomass into biochar and its decoration with CO2 methanation catalysts. We also tackle direct methods of obtaining biochar nanocatalysts, in one pot, from nanocatalyst precursor-impregnated biomass. We review the effect of the initial biomass nature, as well as the conditions that permit tuning the performances of the composite catalysts. Finally, we discuss the CO2 methanation performance and how it could be improved, keeping in mind low operation costs and sustainability

Nonenzymatic nitrogen-doped carbon nanofber-supported NiOx glucose sensor

The glucose electrooxidation reaction at NiOx nanoparticles loaded on a nitrogen-doped carbon nanofber (N-CNF)-modifed glassy carbon electrode (NiOx@N-CNF/GCE) in an alkaline medium was studied. The N-CNF was produced by an electrospinning technique to acquire a large surface area. The produced electrode was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray (EDX) analysis. The electrocatalytic properties of this electrode towards glucose oxidation were tested by cyclic voltammetry and linear sweep voltammetry (LSV). The NiOx@N-CNF/GCE catalytic activity towards glucose oxidation in an alkaline medium was found to be excellent in terms of measured glucose concentration and electrode stability. It showed high reproducibility and stability towards glucose oxidation with activity retention even after 100 cycles of continuous potential scanning. In addition, NiOx@ N-CNF/GCE showed a good linear behavior of glucose concentration detection in the concentration range between 0.0 and 10.0 mM, which highlights its ability to be used as a nonenzymatic glucose biosensor. MYU K.K.Scopu

Pd nanocrystals encapsulated in MOF-derived Ni/N-doped hollow carbon nanosheets for efficient thermal CO oxidation: unveiling the effect of porosity

Rational synthesis of Ni-metal-organic-framework (MOF)-derived hollow N-doped carbon (Ni-MOF-HNC) nanostructures has garnered great attention in various catalytic reactions due to their outstanding catalytic and physicochemical merits, but their activity toward thermal CO oxidation (COOxid) is not emphasized enough. Herein, we tailored the fabrication of Ni-MOF-HNC encapsulated Pd nanocrystals (Pd/Ni-MOF-HNC) for efficient COOxid at low temperature, driven by microwave-irradiation, annealing at 900 °C and chemical etching to form Ni-MOF-HNC that is used as a support for the growth of Pd nanocrystals under microwave-irradiation. The obtained Pd/Ni-MOF-HNC possesses hollow carbon sheets with a great surface area (153.05 m2 g−1), pore volume (0.12 cm3 g−1), rich Pd/Ni-Nx active sites, Ni-metal defects, rich N-content (7.53 at%), mixed Pd/Ni-oxide phases, and uniformly distributed ultra-small Pd nanocrystals (7.03 ± 1.10 nm); meanwhile, Pd/Ni-MOF-NC formed without etching had no porosity and less Ni-metal defects. The thermal COOxid activity of Pd/Ni-MOF-HNC was significantly superior to Pd/Ni-MOF-NC and commercial Pd/C catalysts. This is evidenced in the great ability of Pd/Ni-MOF-HNC to utterly oxidize CO at a lower complete conversion temperature (T100) of 114.5 °C compared with Pd/Ni-MOF-NC (153.8 °C) and Pd/C (201.5 °C) under atmospheric pressure. Conspicuously, the T100 of Pd/Ni-MOF-HNC was lower than those of most previously reported Pd-based catalysts due to the high porosity, surface area, and electronic interaction of Pd/Ni-Nx, and Ni-metal defects, which promote the adsorption/activation of reactants (CO + O2), decrease the activation energy to 73.1 kJ mol−1 and enhance the reaction rate at the same CO conversion percentage. Thus, this study may open the gates for the utilization of MOF-HNC as a support for Pd-based catalysts for thermal COOxidThis work was supported by the Qatar University High Impact Internal Grant (QUHI-CAM-22/23-550), the Qatar National Research Funds (NPRP13S-0117-200095 and NPRP12S-0228-190182), and the NRF/DSI/Wits SARChi Chair in Materials Electrochemistry and Energy Technologies (MEET) (UID No. 132739)

Titanium Carbide (Ti3C2Tx) MXene Ornamented with Palladium Nanoparticles for Electrochemical CO Oxidation

Titanium carbide (Ti3C2Tx) MXene possesses various unique physicochemical and catalytic properties. However, the electrochemical CO oxidation performance is not yet addressed experimentally. Herein, Ti3C2Tx (TX=OH, O, and F) ordered and exfoliated two-dimensional nanosheets ornamented with semi-spherical palladium nanoparticles (2.5 Wt. %) with an average diameter of (10±1 nm) (denoted as Pd/Ti3C2Tx) is rationally designed for the electrochemical CO oxidation. The fabrication process is based on the selective chemical etching of Ti3AlC2 and delamination under sonication to form Ti3C2Tx nanosheets that are used as a substrate and reducing agent for supporting in situ growth of Pd nanoparticles via impregnation with Pd salt. Interestingly, Pd-free Ti3C2Tx displayed inferior CO oxidation activity, while Pd/Ti3C2Tx enhanced the CO oxidation activity substantially. This is attributed to the combination of outstanding physicochemical properties of Ti3C2Tx and the catalytic merits of Pd nanoparticles

Review of recent research on biomedical applications of electrospun polymer nanofibers for improved wound healing

Wound dressings play an important role in a patient’s recovery from health problems, as unattended wounds could lead to serious complications such as infections or, ultimately, even death. Therefore, wound dressings since ancient times have been continuously developed, starting from simple dressings from natural materials for covering wounds to modern dressings with functionalized materials to aid in the wound healing process and enhance tissue repair. However, understanding the nature of a wound and the subsequent healing process is vital information upon which dressings can be tailored to ensure a patient’s recovery. To date, much progress has been made through the use of nanomedicine in wound healing due to the ability of such materials to mimic the natural dimensions of tissue. This review provides an overview of recent studies on the physiology of wound healing and various wound dressing materials made of nanofibers fabricated using the electrospinning technique