Evaluation of dielectric and piezoelectric behavior of unpoled and poled barium titanate polycrystals with oxygen vacancies using phase field method

This article studies the dielectric and piezoelectric behavior of unpoled and poled barium titanate (BaTiO₃) polycrystals with oxygen vacancies. A phase field model is employed for BaTiO₃ polycrystals, coupled with the time-dependent Ginzburg–Landau theory and the oxygen vacancies diffusion, to demonstrate the interaction between oxygen vacancies and domain evolutions. To generate grain structures, the phase field model for grain growth is also used. The hysteresis loop and butterfly curve are predicted at room and high temperatures. The permittivity, and longitudinal and transverse piezoelectric constants of the BaTiO₃ polycrystals are then examined for various grain sizes and oxygen vacancy densities.     

Electromagneto-mechanical fields of giant magnetostrictive/piezoelectric laminates under concentrated load

This paper presents the nonlinear electromagneto-mechanical behavior of magnetostrictive/piezoelectric laminates under three-point bending both numerically and experimentally. The laminates are fabricated using thin Terfenol-D and PZT layers. The three-point bending test was conducted on the Terfenol-D/PZT laminates, and the displacement, induced magnetic field and induced voltage due to mechanical loads were measured. Three-dimensional finite element analysis was also carried out, and the electromagneto-mechanical fields in the laminates were predicted by introducing a second-order magnetoelastic constant for Terfenol-D. Comparison was then made between simulation and experiment.     

Bioprinting a cell-laden matrix for bone regeneration: A focused review

Although many efforts have been made to regenerate the bone lesions, existing challenges can be mitigated through the development of tissue engineering scaffolds. However, the weak control on the microstructure of constructs, limitation in preparation of patient-specific and multilayered scaffolds, restriction in the fabrication of cell-laden matrixes, and challenges in preserving the drug/growth factors' efficacy in conventional methods have led to the development of bioprinting technology for regeneration of bone defects. So in this review, conventional 3D printers are classified, then the priority of the different types of bioprinting technologies for the preparation of the cell/growth factor-laden matrixes are focused. Besides, the bio-ink compositions, including polymeric/hybrid hydrogels and cell-based bio-inks are classified according to fundamental and recent studies. Herein, different effective parameters, such as viscosity, rheological properties, cross-linking methods, biodegradation biocompatibility, are considered. Finally, different types of cells and growth factors that can encapsulate in the bio-inks to promote bone repair are discussed, and both in vitro and in vivo achievement are considered. This review provides current and future perspectives of cell-laden bioprinting technologies. The restrictions and challenges are identified, and proper strategies for the development of cell-laden matrixes and high-performance printable bio-inks are proposed.     

Developments in 4D-printing: a review on current smart materials,technologies, and applications

ABSTRACT

Recent advances in additive manufacturing (AM), commonly known as three-dimensional (3D)-printing, have allowed researchers to create complex shapes previously impossible using traditional fabrication methods. A research branch that originated from 3D-printing called four-dimensional (4D)-printing involves printing with smart materials that can respond to external stimuli. 4D-printing permits the creation of on-demand dynamically controllable shapes by integrating the dimension of time. Recent achievements in synthetic smart materials, novel printers, deformation mechanism, and mathematical modeling have greatly expanded the feasibility of 4D-printing. In this paper, progress in the 4D-printing field is reviewed with a focus on its practical applications. We discuss smart materials developed using 4D-printing with explanations of their morphing mechanisms. Additionally, case studies are presented on self-constructing structures, medical devices, and soft robotics. We conclude with challenges and future opportunities in the field of 4D-printing.     

Surface functionalized nanocellulose as a veritable inclusionary material in contemporary bioinspired applications: A review

The past few decades have seen extraordinary gain in interest for bio‐based products, driven by the intensifying call of the society for petrochemical material replacement and developing materials with next‐to‐no environmental impact. Cellulose, which is an abundantly available “green” material, can be derived from plant fibers and tailored for a plethora of possible uses where it can be used as a substrate or as a filler material. However, emerging technologies and product advancements necessitate the search for materials that are small, biodegradable, lightweight, and strong. Nanocellulose, which can be obtained through as mechanical and chemical production methods with tensile strength and Young's modulus of up to 0.5 and 130 GPa, respectively, proves to be the answer that they were looking for. However, the inherent hydrophilic nature of nanocellulose limited its potential widespread application. Surface modifications of nanocellulose to alter and diminish its hydrophilicity were done to address the aforementioned issues. In this article, we had reviewed on different types of surface modifications and their resulting impact on the properties of nanocellulose and their effect on polymer composites. The importance of nanocellulose in emerging applications such as biosensor, nanoremediation, papermaking, and automotive as well as the current state of the industry and the commercialization progress of nanocellulose were also discussed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46065.     

Mucoadhesive polymers in the design of nano-drug delivery systems for administration by non-parenteral routes: A review

The presence of a mucus layer that covers the surface of a variety of organs has been capitalized to develop mucoadhesive dosage forms that remain in the administration site for prolonged times, increasing the local and/or systemic bioavailability of the administered drug. The emergence of micro and nanotechnologies together with the implementation of non-invasive and painless administration routes has revolutionized the pharmaceutical market and the treatment of disease. Aiming to overcome the main drawbacks of the oral route and to maintain patient compliance high, the engineering of innovative drug delivery systems administrable by mucosal routes has come to light and gained the interest of the scientific community due to the possibility to dramatically change pharmacokinetics. In addition, to achieve the goal of mucosal drug administration, the development of biomaterials has been refined to fit specific applications. The present review initially describes the potential of nano-drug delivery systems conceived for mucosal administration by diverse non-parenteral routes (e.g., oral, inhalatory, etc.). Then, the benefit of the incorporation of mucoadhesive polymers into the structure of these innovative pharmaceutical products to prolong their residence time in the administration site and the release of the drug cargo will be discussed with focus in the developments of the last decade. In addition, the regulatory status of the most extensively used mucoadhesive polymers will be emphasized. Finally, a thorough overview of the different pharmaceutical applications of mucoadhesive polymers will be addressed.     

Effect of reinforcements at different scales on mechanical properties of epoxy adhesives and adhesive joints: a review

Improvement of the mechanical properties of adhesives and adhesive joints has been a subject of great interest in recent years. Up to now, several methods have been presented such as modifying substrate shapes, adding microparticles (MPs) and nanoparticles (NPs), and embedding micro and macrofibers in the adhesive layer. This review aims to investigate how these reinforcements of different scales in the adhesive layer influence the mechanical properties of adhesive joints and adhesives. Characteristics and applications of reinforcements are introduced in the first part. In the second part, the effects of several parameters commonly investigated by researchers on the strength, stiffness and fracture toughness improvement of polymeric materials are reviewed for reinforcements of different scales. Finally, damage mechanisms involved in increasing or decreasing the mechanical properties are reviewed and discussed.     

Modelling of a moving bed furnace for the production of uranium tetrafluoride Part 1: formulation of the model

Reduction, followed by hydrofluorination of uranium trioxide UO₃ to produce uranium tetrafluoride UF₄ is one of the stages of the French nuclear fuel making route. This dual operation is carried out in a specific reactor known as a moving bed furnace, consisting of a series of steel cylinders that form an L. In this first part of a two-part paper, the mathematical modelling of the furnace is presented in detail. The model describes solid and gas flow, heat transfer by convection, conduction and radiation in the moving bed and in the walls of the furnace, and chemical reactions. In the vertical part of the reactor, mass, momentum and energy balances are solved using the finite volume method. The horizontal part is modelled by a cascade of stirred gas and solid reactors. The assumptions and equations of the model, as well as the boundary conditions and numerical solution techniques are detailed. An example of calculated results is presented and found to agree satisfactorily with available measurements. Application of the model is discussed in Part 2.     

Modelling of a moving bed furnace for the production of uranium tetrafluoride. Part 2: Application of the model

The French nuclear fuel making route uses, prior to enrichment, uranium tetrafluoride UF₄ obtained from the reduction, followed by hydrofluorination of uranium trioxide UO₃. These two steps are carried out in a specific reactor known as a moving bed furnace. We developed a steady-state numerical model of the moving bed furnace, described in Part 1. In the Part 2, calculation results for a reference set of operating parameters of the furnace are presented in term of temperature, reaction rates, solid and gas compositions. Results analysis enlightens the detail of the furnace behaviour in its different zones. Unknown features have been revealed, such as thermodynamic limitation of the hydrofluorination reaction in the hot core of the moving bed. A sensibility study of various operating parameters shows how some can influence the UF₄ quality and underlines the strong coupling between the different zones of the furnace. Finally, the model is applied to define an optimal temperature progression in the furnace and suggests geometrical modifications. Besides, the validity of using the law of additive reaction times for calculating the reaction rates in such a reactor model has been checked for the first time against a numerical grain model.     

Support surface pore structures matter: Effects of support surface pore structures on the TFC gas separation membrane performance over a wide pressure range

In this work, the effects of support surface pore structures(including surface pore size, surface pore density and surface porosity) on the performance of thin film composite(TFC) gas separation membrane over a wide pressure range(from 0.3 to 2.0 MPa) were studied. To fulfill it, the polysulfone(PSf) supports with different surface pore structures were prepared. Two kinds of wide-accepted polymeric membrane materials, i.e., polyvinylamine(PVAm) and Pebax 1657 copolymer, were used as skin layer materials. We pointed out for the first time that the support surface average pore size and pore density could affect the chain mobility of polymer of skin layer at the support surface pore entrance, then, can affect the TFC membrane performance. Besides, we also discussed the effects of support on the TFC membrane performance when the feed pressure changes for the first time. This work can provide guidance for choosing a suitable support for TFC gas separation membrane.